1. Past hour
2. ## Battle arena needed!!!

Hi. I along with a couple of friends are working on a project for an arena fighting game. This game, if it ever sees the light of day, will be a third person over the shoulder style cartoon/anime game inspired by the likes of Powerstone (Sega Dreamcast) S4 League (PC) and Splatoon (Nintendo) What we need is ONE (singular) arena to show off for a potential demo of the game. This will need to be a Team Deathmatch/Free For All map that can accommodate at least 10 players. We're looking for features such as destructible terrain, traps, and lots of places to run and hide. If you're interested in helping make a demo map, please send us a private message.
3. ## I Know Nothing and I want to change that

A simple way to put the difference between C# and C++ is that you can think of C++ as a random assortment of powerful machine parts. Where C# is a already build machine with a purpose. For example, Unity was made with C++ but the people who use the engine actually use C#.
4. ## I Know Nothing and I want to change that

No. There are many differences outside of memory management. A quick google search will give you an extensive list of examples showing the differences between the two languages.
5. Today
6. ## Tower Defence Progress

Looking very good!
7. ## Tower Defence Progress

" I must admit I'm kind of looking forward to wrapping up and working on the next thing, so am thinking more in terms of what I need to finish." I hear yeah, I find that switching from one project to the next week to week is tough. There is a motivation drain at the beginning of every week.
8. ## I Know Nothing and I want to change that

So biggest newbie question I have is. C# automatically assigns a memory value and C++ does not. That's the difference right?
9. ## I Know Nothing and I want to change that

There is nothing equivalent with Unreal. However if you are starting with Unreal you should be using Blueprints, not C++ till you have a grasp of programming. However Unreal like C++ isn't beginner friendly. You can start with Unreal, there is lot's of bonuses to doing so, but it will be a rocky road at the least. Since you are going to college you should probably start with Unity, it uses C#. It's the one most colleges use to train developers. Unity and C# is much easier to learn than Unreal and C++. Because Unity is 10 times easier to use than Unreal and has 65-70% of the power, it is Unreal's biggest competitor. Or at least Unreal is Unity's biggest competitor. Starting with Unity and switching to Unreal (or whatever engine is popular at the time) is a good strategy.
10. ## Simulating Cursor For Textbox In SDL2

I'm an idiot (ie. I can't use google well), finally found out about TTF_SizeText().
11. ## I Know Nothing and I want to change that

Got ya. The only reason I was trying to learn c++ first was because I was going to use unreal engine. Is there one that uses C# that is equivalent
12. ## I Know Nothing and I want to change that

Learning C++ as your first language is like deciding to climb Mount Everest as your first mountain. It can be done but is very harsh and many loose hope that way. C++ is a extremely difficult language, it does no cleaning up for you, is one of those languages that believes the programmer is always right and has no safety systems in place. Learning C++ first could be confusing. Most C++ tutorials will expect you already learned the basics of programming; they will not explain to you what you are doing or why. It could be why you have been having such a hard time to understand programming. It's recommended you start with Python, C# or even JavaScript, any other object orientated language will do.
13. ## BGP DevLog #172 (Map Mastery)

The Map System I've been subconsciously dreading has finally been implemented and the rest of the menus are coming together bit-by-bit as I program all the pieces separately and connect them together (instead of cramming everything I could into one giant, unreadable script like before). The results? See the latest gamedev update to find out.
14. ## 2D Can I represent a 2x2 matrix by a full affine matrix?

like this? const D3DXMATRIX robertx = D3DXMATRIX(1, 0, 0, 0, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1);
15. Yesterday

Why not?
17. ## I Know Nothing and I want to change that

If you're using C++ and you want to use the iostream header, then you'll have to include it. It doesn't matter if it's above other includes or in between other includes. I hope you're not learning C++ as your first language. I would highly discourage this.
18. ## I Know Nothing and I want to change that

Hey I have a question. Should my code always start with #include<iostream> or does it depend on the situation?
19. ## Separating components of a free form rotation

Poor final editing on my part. My bad. I re-edited that sentence to make it clearer. Thanks for this. I learned a few new things from your decomposition suggestions. As for the original issue, I had to re-think the whole thing when you pointed out that you're not sure if this actually helps. And it doesn't; the change of axes in rotation always causes "jitters" when the components I provided above are decomposed. I ultimately solved this by interpolating the actual screen delta values, and then recalculating a new Quaternion every frame.
20. ## How to Build a Game in a Week From Scratch with No Budget

There are many great resources available to small, budget-conscious independent game developers today. On a public forum, in a counter-rant, I expressed this fact by bragging that if you gave me a week, a fresh install of Windows, and a good Internet connection, I could build a halfway decent game with no budget whatsoever.
21. ## MobileWeek 10: Randomization and GoFundMe update

Hey All, Much smaller update this week. Was focused mainly on code writing. I have finished all the code for the room randomization and have almost finished testing it. So far it’s working great and exactly what I wanted. With my calculations with room Type A all being random from a pool of 25 different layouts and with enemies always random there’s only 1 out of over 2.6 million of a chance getting the same world layout. I think it’s safe to say you will never play the same game twice. Out of those 25 different room layouts there will also be puzzle rooms incorporated with that. Mostly consisting of moving boxes to switches or to clear a passage way. For the next couple weeks I will be focusing on art work. I will be making different color walls so there’s some variation. Once all the rooms are done I will begin coding the puzzles. I do need 1 more room hazard. This will be a household object that will shoot “something” out. I would like some ideas if you have any in the comments. I’ll pick the one I like and draw it up and give you credit for the idea in the games credits! The only thing I have so far is a washer machine throwing rolled up clothes. So let’s hear some ideas! Also the GoFundMe has almost reached the goal of $500 dollars!! Thank you to everyone who donated and shared. Please don’t stop we are so close. https://www.gofundme.com/help-family-with-cancer Also I would like to announce the game will now also be released to android devices as well as IOS. Till next week, take care and thank you. 22. ## Providing equal opportunity for each player If you have a map which is 8 * 8 (w * h - Full Map), I would generate the 4 * 8 (w * h), then mirror the array data for the other half if you're looking at an equal map. Just feed the 1st array into the 2nd but mirrored, and now you have a symmetrical map when you print both arrays out. You'll have to offset the positions for the other half unless you're feeding both arrays into one for the actual drawing part. In my own RTS projects I always programmed a level designer which did this for me, and I couldn't imagine hard-coding RTS maps as a long term option. 23. ## Incorrect angular collision response Thanks, tomorrow I'll definitely give it another try to understand what you're doing differently, hopefully getting closer to solve this mystery. 24. ## checkers I'm confused as well regarding the specifics but I'll try anyhow. As long as you're using some form of a map like a 2D Array, and if your game is using official tournament rules there shouldn't be any issue with setting the proper jumps. If you're allowing the player to optionally refuse double or triple jumping then you need to either put a movement queue in place, or stop the jump at the dropped position. If the issue is your code for movement is getting looped through over and over when you only intend it to run once per movement cycle, then you either need to handle the mouse click through an event manager that sets a boolean that an action has taken place, then run your logic and wait until another event, or program this to cycle once through your real-time input in your logic step. I would also run it on a one stop cycle which means when you move the piece you have an algorithm which determines the jump path, then it executes it and stops as opposed to moving, checking, moving, checking, in real-time per tick. 25. ## Latest from GameDev.net - May 2018 No reason to feel bad. GameDev.net is intended to be a platform for the games industry to learn, share, and connect with each other, and money is a very real part of that. Your account's Pixels are effectively a virtual currency - even though I haven't setup a way for Pixels to be used yet. Only one author/member profile can be attached to a tutorial - it's just the way the data is stored right now. But there is a field for author names that can include multiple people. Not ideal, but it's something. 26. ## Good Community Management/Marketing companies? Depending on your needs and product, I offer a number of marketing and community management services through my Patreon. And I'm probably the cheapest marketing pro out there at the moment as I continue to build my client base. I have a background in digital marketing like websites, social media and email for big, big companies (American Airlines, Capital One, 7-Eleven) and now I'm applying my industry knowledge to my passion: indie games! ...And I just put out a new book for Indie Devs called Dark Alley Marketing. Feel free to contact me via Twitter if you want to discuss further. Or you can enjoy all the free stuff on my Patreon page. Good luck! 27. ## I Know Nothing and I want to change that Okie dokie I'm off to study a little and practice thanks for everything 28. ## checkers I'm assuming mouseMotion is called in a loop/every frame. This also means that black_piece is called every time. Inside black_piece, you set some flags to be true, depending on where the mouse cursor is. Inside move_piece, you check some flags, and force the other flag to be false. But since mouseMotion (and thus black_piece) will be called the next frame as well, the flag you set to false can get set to true again. That is, flag[4][0] can be true and set flag[4][2] to false, while the next frame board[4][2] can be 1, which will set flag[4][2] to true, which will end up calling drawScene_move_two. I have no clue how to solve the problem you have. I don't understand what you're trying to do, based on the code you have. The tiny amount of code you've posted hints at very strange decisions and architecture (which is the same as things have been the last x years you've been posting here). I have no clue what "board" or "flag" is supposed to mean, and I honestly doubt looking at more of your code will make things clearer. ## Members You Follow #### You must be logged in to view this content. Don't have a GameDev.net account? Sign Up ## Popular Entries ## Recent Blogs 1. The Map System I've been subconsciously dreading has finally been implemented and the rest of the menus are coming together bit-by-bit as I program all the pieces separately and connect them together (instead of cramming everything I could into one giant, unreadable script like before). The results? See the latest gamedev update to find out. 0 comments 2. Hey All, Much smaller update this week. Was focused mainly on code writing. I have finished all the code for the room randomization and have almost finished testing it. So far it’s working great and exactly what I wanted. With my calculations with room Type A all being random from a pool of 25 different layouts and with enemies always random there’s only 1 out of over 2.6 million of a chance getting the same world layout. I think it’s safe to say you will never play the same game twice. Out of those 25 different room layouts there will also be puzzle rooms incorporated with that. Mostly consisting of moving boxes to switches or to clear a passage way. For the next couple weeks I will be focusing on art work. I will be making different color walls so there’s some variation. Once all the rooms are done I will begin coding the puzzles. I do need 1 more room hazard. This will be a household object that will shoot “something” out. I would like some ideas if you have any in the comments. I’ll pick the one I like and draw it up and give you credit for the idea in the games credits! The only thing I have so far is a washer machine throwing rolled up clothes. So let’s hear some ideas! Also the GoFundMe has almost reached the goal of$500 dollars!!  Thank you to everyone who donated and shared. Please don’t stop we are so close.  https://www.gofundme.com/help-family-with-cancer Also I would like to announce the game will now also be released to android devices as well as IOS.  Till next week, take care and thank you.
By SOS-CC
3. Im really excited to show you this big jump in my game. INVENTORY is there !! Ive been sent by school on practice, so my time was limited but I still managed to make it. It it working, how I intended and it has some cool effects, that I wont show you yet. Now I will have more time to make better fight system and make it more polished, that its able to make interresting characters. I want to make more enemies to fight, so you wont get bored with by beta.  And again... my artworks are bad for now, so look from safe distance.
4. STORAGE AREAS AND CONTAINERS: Today Aaron is working on the Storage Area functionality.  He’s made it so the storage area can be moved, and is currently working on the ability to remove it entirely.  The idea is that when a storage area is removed, the contents remain on the ground and will tagged for hauling to a new storage area by your units.   The same thing should happen if a refrigerator gets destroyed.  You don’t want to necessarily destroy its contents, just the fridge itself.  So the contents will have to spawn on the ground and get hauled to the highest-level storage area.   Once this is done, we will have paved the way for storage areas and containers to have filters on them, allowing the player to choose which types of resources allowed into each container and storage area.   FEELINGS AND RELATIONSHIPS: I am working on the relationships and feelings that the units have for one another.  We’ve built a test-mode where we can simulate various deeds and actions done by and to different units to explore the ramifications of each deed.   For example:   Pearline attacks Erasmo a bunch of times, so Erasmo strongly dislikes Pearline.  Pearline then flatters Marion 4 times in a row, so Marion loves Pearline.   Something weird happens when I have Pearline then commit a negative deed to herself.  When I have Pearline kill Pearline, Erasmo, who hated her before, suddenly had a positive opinion of Pearline.  Then Marion, who loved Pearline, suddenly mildly dislikes Pearline.   The reason for this is that units will have negative feelings for someone who does something bad to someone they love, even if it is something the person does to themself.   We will either have to avoid having units commit deeds to themselves, or I will have to put a check into the Love/Hate evaluation function to do something else if both the actor and target of the deed are the same unit.   I’m also adding delegate events into the Love/Hate plugin to cleanly send data to the UI so that we can show the player the current status of the relationships between units.  These will also allow us to show the various factors influencing the units’ happiness/unhappiness levels, so that they can do something to keep the units happy.   Eventually, we will make it so that a unit who is extremely unhappy and has a negative opinion of the colony will choose to leave it.  Also, if a unit hates another, they may get into a physical brawl, or engage in other nefarious deeds against the loathsome one.   Next steps are to get the Gossip functions working properly to share information about each other and sway each others opinions about each other.  I’m hoping I can also use this to initiate general conversation amongst the units while they are near each other.
5. After a few days away from home I've done a bit more on the game. I must admit I'm kind of looking forward to wrapping up and working on the next thing, so am thinking more in terms of what I need to finish. The towers now have separate logic and firing / sounds. There are just 3 so far but I'll probably add another 2 or 3. Don't know if I have the energy to put in an upgrade path for tower technology .. maybe if people play it lol. The enemies now attack towers as well as your base. The AI for this is pretty simple, and they have no collision detection, so just go for the tower that attacked them. Maybe I will put in collision detection but it potentially opens up a barrel of worms (avoiding stuff) so I may leave on the todo list. Towers have health and once they are destroyed they stop working and have smoke coming out. You can repair them by clicking, this costs money in proportion to how damaged they are. The building placement is a bit better now, there is a zone around houses where other buildings will not be placed so they aren't too close together. The buildings and props serve no function as yet except they prevent you building towers on that spot, so you have to be a little strategic to where you build. As I'm a little worried the unity terrain is not practical both in terms of installation size and performance, I've just today put in some procedural texturing of the ground block underneath the play area which I am using as an alternative to unity terrain. It looks okay now after some research into how this was possible, I did it with just software texture splatting and precreating the texture on level load. On the terrain front I plan to vary this and the buildings / trees etc as you progress through the levels, so it doesn't look all the same. I should probably also put in a high score table, as it feels a bit of a let down when you get a long way then fail a level. But that depends how easy it is to put in a keyboard to type in a name, as it might not be played on a desktop. Actually I've no idea if it will work on other platforms but I'm hoping unity will handle most of that automagically. The controls are pretty tablet friendly so far. A big issue to confront will be installation size. I'm not sure yet what this depends on but it seems ridiculous when I've done test builds (187 megs last time). Hopefully I can get some kind of build log to find out what is being included in assets and strip out a load of unneeded stuff and oversize textures etc.

6. Yeah, time has come for another progress follow up. So, in short terms, we made the game "look better". (Modified the bloom algorithm a bit and added more animations) Also, in this level there can be seen some Damage Bees. This is the first time they appear in the game. This is the video: https://www.youtube.com/watch?v=nsvbuYaV6ts Btw, we now have a website, not sure if I mentioned in the past. Here's the website: https://wemakepizzagames.tk/ And as always, thanks for following the developement of the games we make at Pizza Games!
7. 5/22/18 Art dump! Apologies for the long distance between updates. We have been working on some more technical aspects of gameplay as well as try to integrate shadow/shading into the code and tilesets. We've also been discussing plot. by liquid_pencil Meanwhile, I've got some artist monster concepts made as well. by Blakkfox by Blakkfox by Blakkfox by Blakkfox, liquid_pencil Somewhat unrelated, I did some non canon character art for Plague (TW:Blood) And some sprites that have been readjusted to a custom color palette by liquid_pencil   by Blakkfox, liquid_pencil by Blakkfox, liquid_pencil by Blakkfox, liquid_pencil by liquid_pencil by liquid_pencil, Jonathan Amo by liquid_pencil by Blakkfox, liquid_pencil by Blakkfox, liquid_pencil by liquid_pencil by liquid_pencil
9. Official Game-Guru News: So there's a lot of traffic at this point on Game-Guru.  Lots of bugs being squashed.  Looks like lighting is getting looked at, specifically an SDK called 'enlighten' as a possible solution.  In the meantime there's a host of new functions on the github iteration of Game-Guru that are lighting related.  Looks like I might need to go make an Advanced lighting kit :)  ...

Also in official news there apparently progress being made on an underwater state for the player, which should really open up the gates as to how water is handled.  Lastly it appears that mega pack 3 has gotten more PBR assets - the roofs really pop with the shine they have now!

Check it out here:
https://www.thegamecreators.com/post/gameguru-mega-pack-3-dlc-update-2

New Products On The Store:

So a few new things available.  I'm really digging these complex and ornately textured lamps by Mad Lobster.  Reliquia has made some absolutely amazing skies which you should absolutely take a look at.  I've noticed that the quality on campana production's models has gone up, check out this cow skull!  And lastly Shadow Man appears to continue to be on his building-making rampage.

Free Stuff: Good lord, there's a crateload.
https://forum.game-guru.com/thread/219680 - A must have ... Reliquia has put 16 free zombies up!

https://forum.game-guru.com/thread/219692 - Lafette II has put up two zombie kids and some desert props.  Be aware that having shootable children may violate local laws (Notably in Germany).  Caveat Emptor.
https://forum.game-guru.com/thread/219523 - Here's a good AI script for the soldier, a wandering type script.

So from here, I'm going to stop and just sort of separate things so you can really get a sense of how important these next two are.

https://forum.game-guru.com/thread/215012?page=16#msg2600572 - This has been a Long, LONG time coming.  Amenmoses and Bod have teamed up to make a really awesome vehicle script for a truck - this looks and feels awesome.

https://forum.game-guru.com/thread/219628 - Honkeyboy has added his own flavor to the drivable vehicle scene with this racing bike script!

Those two should keep you busy for a while.  Amazing stuff, truly.  Looks like I owe someone a prize from my bounty board!

Third Party Tools: I'm working on the notepad++ update.  It's a lot of work because they keep making updates over at github!  But it's coming along.  There's a LOT of XML to pour through and verify/cross check.

Random Acts of Creativity: https://forum.game-guru.com/thread/219296?page=1#msg2600665  - DK's latest update in his wasteland saga.  Looks good though personally I gave him the following input on discord:
"So observations @Duchenkuke for your test #3 - 1) I don't like the new coloring. There's not enough contrast. It looks too black, white, grey, and drab. Sorry! 2) The inventory looks easy to use but I'd really work on cleaning up the interface elements. Maybe use a color other than white (maybe a white-orange?), some asymmetrically sized boxes, etc. 3) The vehicle was awesome. What kidney do I have to give you so I can build a truck driving game for my son? Overall though your level design looks fantastic. Your use of clutter is second to none and honestly aside from the coloration issues I'd say you're coming along really well."

In my own works:
I'm continuing to procure more items and art for the book's sidecar modules.
It's a lot of headache but at the same time there's a big payoff for those who will purchase by getting a combination of high quality free, store, and exclusive assets.

10. After 2 and a half years learning, practicing and making small games, as a team we decided to make the
next step and make a commercial game. We know that we have a lot to learn yet, so for this game we're going to focus on the abilities we already have. This way the development will be faster and don't will be delayed for getting stuck in code
or sprites too hard to make. We have more experience making platformer games, so we're going for that direction, also we think it's
easier for making sprites, coding, and animation. if you're interested check the first game we released as a team!
Gamejolt: https://gamejolt.com/games/umbral/153048
Itch.io : https://rengy.itch.io/umbral   Fist sprites for Cow vs the Pig Empire

## Latest News

1. CGTrader’s birthday sale is on May 22-29 with over 250,000 3D models (for games, VR, architecture and 3D printing) going on sale for up to 50% off. 3D artists are giving discounts to celebrate the 7th birthday of the marketplace that has the fairest conditions for designers worldwide. Here’s a link to the sale page - https://www.cgtrader.com/sale
By khawk
3. The EnhanceMyApp podcast is back with a brand new episode. Joined by David Hu, Director of User Acquisition for NCSOFT, the podcast discusses how to obtain new users on a budget and properly analyze user acquisition data to create a monetization strategy for your mobile app. Check out the EnhanceMyApp Podcast here.
4. Final Lens Effects package is now available on the Unity Asset Store. A free Demo (full-featured) is available for download.

About Final Lens Effects The Final Lens Effects package is a collection of image effects for simulating some properties of real camera lens such as depth of field, vignetting and distortion for Unity 5 (5.6 or higher). Package contains following effects: - Depth of field effect with polygonal aperture (Bokeh)
- Bloom effect
- Vignetting
- Chromatic aberrations
- Lens distortion
- Tone Mapping (ACES)
- Color LUTs Support

These effects can be used to make your scenes look closer to as if they were captured with real camera and lens - making computer generated graphics look more natural or to achieve the "cinematic look" for cut scenes or in-game. Being very tweakable, the effects can be combined, reordered, customized and overdone to create interesting looks or visual effects.
By khawk
6. Amazon announced Sumerian at AWS re:Invent 2017 but today announced its availability to developers. Sumerian is a web-based visual editor that allows creators to develop 2D, 3D, and VR experiences without having to master specialized tools.  Experiences can be deployed across multiple platforms without having to write custom code or worry about deployment systems. From the announcement: Learn more from the Amazon blog here.
By khawk
7. Valve has released a new version of the OpenVR SDK. The 1.0.15 release introduces SteamVR Input, allowing users to build binding configurations for their favorite games with any controller, ultimately making it easier for developers to adapt their games more easily to diverse controllers. From the announcement: Learn more from the StreamVR blog announcement here.
By khawk
8. Active Gaming Media Inc. and indie game platform PLAYISM has announced a new collaborative project with KADOKAWA Corporation (CEO: Masaki Matsubara; HQ: Tokyo, Chiyoda-ku) on the latest title in the Maker series: Pixel Game Maker MV.  Pixel Game Maker MV is a game creation software that lets you easily create your very own original action games, without any sort of programming skills or specialized knowledge whatsoever. The action games you can create are limited only by your imagination.

The ability to use original materials and resources for character animations, background maps, sound, etc., allows you to create truly unique games. Games can include physics, multiplayer capabilities, particle systems, user interfaces, animations, and more. Learn more at the Pixel Game Maker MV website at https://tkool.jp/act/.
By khawk
9. Perforce Software, a provider of solutions to development teams requiring scale, visibility, and security along the development lifecycle, announced a new package offer for independent game development studios. The package, called the “Indie Studio Pack,” is designed to provide up-and-coming game development studios with the tools they need to plan and version their next game. It includes five free users on both its version control and project management solutions: Helix Core, a long-time industry standard, and Hansoft, an Agile project management tool built by game developers for game developers. Recognizing that independent studios come in many sizes, the package includes special pricing for those needing more than five users. The offer comes after real feedback from game developers at the industry’s largest global event — the 2018 Game Developer Conference (GDC)held last February in San Francisco. “What we heard at GDC is that indie game developers love Helix Core, which is currently available for free to teams of five or fewer, but they wanted similar access to our Hansoft project management product,” says Nico Krüger, Perforce General Manager. “So, we’ve bundled them together.” In a crowded field of project management tools, Hansoft is one that was built by game developers for developers. It’s currently used by AAA studios for its speed, flexibility (it supports Agile and hybrid methodologies), and scalability. “[Indie game developers] told us that what they end up doing is using free project management software they find online — and there’s a lot of it these days — but that those tools aren’t really built for game developers,” says Krüger. “They now have access to the same version control and project management tools used by AAA game studios.” Visit the webpage for more details about the Perforce Indie Studio Pack.
By khawk

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## Recent Articles and Tutorials

4. The Game Dev Loadout podcast (here and here) has shared their recent Cliff Harris interview with us. The original interview transcription is at Game Dev Loadout. You can also see more podcast interviews from Game Dev Loadout here on GameDev.net. Game designer, programmer, and running a one-man games business, Cliff Harris of Positech Games (@cliffski32 on GameDev.net) is behind strategy and simulation games such as Production Line, Democracy, and Gratuitous Space Battles.  In this interview, Cliff talks about his journey in the game industry, emphasizes on making sure you are taking advice from the right people, and why you need to invest in a great chair for yourself and your team. How did you get started in the game industry? I started programming as a kid when I was 11 on a tiny home computer and then I kind of got out of computers, had all sorts of weird careers working on the stock market and in I.T and boat building and playing the guitar. I taught myself C++ from a home study course on floppy disks then I started making games and that was 20 years ago so it was before indie games were really a thing. I worked at Elixir Studios and Lionhead for 3 years and then I quit that and been full-time indie ever since. What was that push that made you join the game industry? At that time in the U.K, you couldn’t get a job as a programmer unless you had a former qualification as a programmer or you already had a job as a programmer. I always wanted to program video games like a lot of people did and it became possible with the internet that you could program games from home. It was a hobby that turned into a career and a proper business. What is something we probably don’t know about in AI mechanic that we should know? The thing that people don’t realize about AI is that it’s very easy to make something seem alive with few lines of code. Like I have two cats and they really both are predictable. Sometimes the way my cats behave I think you are just few thousand lines of C++. When you break it down, it’s not that difficult to program NPC’s in games that behave and move in quite a natural way. It’s funny because some stuff that you consider easy, it’s almost impossible. So like finding your way out of a maze, we’re pretty good at that but computers are rubbish at it. If you want to program an NPC with text so that it seems to converse with you in a way that doesn’t seem too scripted, that’s not too hard. The reason people tend to encounter rubbish NPC in AI games is due to an obsession with having voice acting for everything. It’s easy to program an NPC that can talk to you about 100 different topics with thousands of different variations that sound fluent and responsive to you. But if you want to record a thousand lines of dialogue and you have got some big name actor then, you can’t afford it. So that’s actually the bottleneck. The other possibility is the translation. The problem is the minute you translate it to German, it’s absolute chaos. The sentence structure is different and you obviously have to pay a little bit to translate the text into German. And if you have got like 20 languages and there are tons of different phrases in each language, suddenly that’s what becomes expensive and difficult. But as you program, it’s fairly easy and fun. Production Line Would you suggest new developers stick to text or voice acting? If you want to capture the whole audience and to have a successful indie game, you probably are going to want it in like 10 different languages. So to get it professionally done is probably like 10 cents a word. So every time you type like one line of dialogue, it’s going to cost you like 50 dollars. If you want to record the audio and then you want that in 10 languages, that’s going to cost you even more. And does it really add to the experience? I’m not sure it does. And the other thing is that I am very impatient and I value time a lot so I’d rather read the dialogue personally than hear it. I want to talk about the worst moment of your career, that one moment that’s still vivid in your mind. They are a few. I have left a game company in a very heated argument, which is funny because I recently bumped into the guy I had that argument with and he’s fine, and I am fine and we get along, but it was just really stressful. I have had bugs that are really bad. I had a bug that could potentially destroy someone’s computer and someone reported a problem to me and I was like “No, I am sure this is not a bug of mine” and I looked into it and I did a lot of experimentation to get this bug to trigger on my PC. I thought “Oh my God, I cannot believe I had made this mistake.” Yeah, I remember frantically coding this patch for it and putting it out immediately and no one else got infected by it. But I was really worried. It was a very rare circumstance but it would delete stuff on your hard drive. It started happening to me but people had anti-virus so it was like a flag going “Hey, what are you doing?” That’s a reputation-destroying bug that deleted a file where the player goes to delete some content intentionally and under certain circumstances, the file name that would be passed in would be empty and given the structure of that code it would then start to delete everything. I had to make loads of checks in all of the areas of my game that can never delete a file. There’s so much code wrapped around this and I can never ever get into that position again because that was bad. From the heated argument story, how did you handle the situation and what was the outcome? Well, I handled it badly, actually, everyone handled it badly. I mean, I had been in this company too long and I was very frustrated and sort of wanted to leave but I had stayed on the assumption that things would change. I just lost it, I got into a very strong argument and someone there had stormed off. And that was it, that was how I left. Looking back on it, I stayed in the company too long. I am very Indie, I don’t like working for other people. I am not very easy to employ because I am quite outspoken and maybe not massively respectful of authority. So it was kind of like a bad fit. To be honest I have stormed out of another job as well. So what should we take away from that experience? The game industry is a lot like the music industry because almost everyone in the music industry makes no money and some people make piles of money. And then there are many more people who want to be in games than the industry will support, which is a lot like music. So you end up with very stressed people who are doing what they love doing, they are very passionate about it and very intensely into it and they are working very hard. It is basically a recipe for everyone to get into huge fights and hate each other. It’s a bit better now I think but there were a lot of companies where people would work very long hours and they would work very late and they go beyond what you would normally put into a job. They aren’t massively well paid at any point. Also, the game industry attracts people like me who are fairly introverted, so we have good technical skills but not very good people skills. You put all that together and it is going to be tough. But I don’t think people hold grudges, I mean I have had two huge arguments with people, some famous and some not and always ended up getting along with them because ultimately very few people come into the industry for money because there isn’t much. So generally you realize that everyone is here just to try to make cool games and work on great stuff no matter how much we like kind of get on each other’s nerves. What are bad recommendations that you hear in your profession? There are a lot of people that will give you advice. Like if you go on to Reddit and sort of say “Oh I am thinking of making this game, oh I am thinking of porting to this platform”. You will get a massive amount of advice and almost all of it will be rubbish. That’s because the people who are always on Facebook, Twitter and Reddit, just sit there, waiting on giving advice to others. I am never like I have to go there and post it and see if anyone is ever asking about something I know about. I’ve read a huge amount of stuff that says there is no point in advertising your indie game. Some of them might say that I have spent like a $100 on Facebook Ads, I didn’t notice any difference in the number of downloads of my game and what you can take from that is you know one person who spent a$100, they did not receive a direct difference. I’ve spent $265,000 on Facebook Ads over the years, so as you can imagine I am pretty convinced they work. But what I am saying is that I have literally a thousand times more data points on that issue. So if you see me talking about the Pro’s and Con’s of Facebook Ads, well I know what I am talking about. If you hear me talking about whether Android or iPhone is a better platform, then just slap me and tell me “Cliff you have no idea, no you don’t know anything about it”. Because you have never made a mobile game and I think that’s the most important thing, you have to know whose advice you are taking and on what basis. We will have an intuition about games and stuff and what should work, what shouldn’t work and often our intuition is wrong. I honestly think that free to play should not work but it clearly does. I think that there is no way you can run an entire games business based on selling virtual hacks, I know that cannot possibly work. But I know it does. So you have to listen to specific people on specific issues. What is one of the best investments you have ever made? Could be an investment in time, energy, or money. Okay, I’ll give you two, time and money. The time thing is learning how to code my own game engine. I learned to code everything like graphics, sound and whatever from scratch because I had to. It gives you a big insight into performance and why your game may be slow. I get to code very fast stuff when I need it. Also, I am not relying on anything else. I am not paying any money to Unity and if they update Unity or Unreal and it breaks everything, obviously I don’t care because I am not using it. So that’s given me an independence that’s very helpful. Obviously, it takes a lot of time. Gratuitous Space Battles The physical thing which I have told a lot of people over the years is this chair that I’m sitting in. If you’ve got a tech startup and you have coders and you have money then buy these Herman Miller Aeron chairs for everyone. It was 800 pounds which is a lot,$1100. I am fully aware that it’s a crazy amount of money. But I sit on it ten hours a day and they last forever. It affects your health and mood. It really is a good investment and even if you think it’s kind of over the top and unnecessary. Don’t buy a $20 chair from a cheap shop. Make some sort of investment in your comfort because in the end you spend a lot of time sitting in front of the keyboard and it’s so much better for you to be comfortable when you do that. BETA PHASE: Rapid Fire Questions What was holding you back from joining the game industry? I don’t know. Nothing would stop me right now but back before I joined, the industry was tiny. It was not something people did. Nobody knew anyone in the games industry, but now nothing would hold me back. Back then it was just like “that’s not a real job”. What’s the personal habit that contributes to your success? Getting out bed early. I was a real workaholic. I would be working at my desk by 8 o’clock, which doesn’t sound that early but for a computer programmer, it is because then we work till like 8 o’clock in the evening. Just learning how to get out bed and go straight to work without messing around, that’s the best thing. What’s the best piece of advice you’ve ever received? Ask for more money. Most of the time you don’t get it, but occasionally you do and it’s just like free money and you’re like “Hey, they weren’t going to give me that unless I said it”. It’s really awkward but do it. What’s that great marketing tip to make yourself and your game stand out? Put faces in your games. Read into Neuroscience, a disproportionate amount of your brain is dedicated to looking for faces and looking for emotions in faces and if you have three images of games and if one of them has a face in the image, that is the one everyone looks at first. What resources should we game developers use to get started today? If you are technically-minded and if you want to be a programmer more than anything else, then buy some good C++ books and learn how to code everything from scratch. If you’re not, then use Unity but don’t put off the idea of coding from the ground up, it’s very valuable. Imagine you woke up the next morning in a brand new world and you knew no one, you still have all the experience and knowledge you currently have today, your food and shelter are taking care of and you have a laptop. What would you do step by step on the path to join and become successful in the game industry? I would make a PC strategy game and sell it on Steam. It would be 2D, top down. I would find an artist to do like revenue share on it and I would do all my end marketing and game designing and code it from scratch, probably don’t even need ‘Unity’ to do that and it might even be easier. That’s the safest and best route to actually making a game that will make money. You can listen to the entire podcast and more interviews with developers and others in the industry at Game Dev Loadout. 0 comments By khawk 5. I recently worked on a path-finding algorithm used to move an AI agent into an organically generated dungeon. It's not an easy task but because I've already worked on Team Fortress 2 cards in the past, I already knew navigation meshes (navmesh) and their capabilities. Why Not Waypoints? As described in this paper, waypoint networks were in the past used in video games to save valuable resources. It was an acceptable compromise : level designers already knew where NPCs could and could not go. However, as technology has evolved, computers got more memory that became faster and cheaper. In other words, there was a shift from efficiency to flexibility. In a way, navigation meshes are the evolution of waypoints networks because they fulfill the same need but in a different way. One of the advantages of using a navigation mesh is that an agent can go anywhere in a cell as long as it is convex because it is essentially the definition of convex. It also means that the agent is not limited to a specific waypoint network, so if the destination is out of the waypoint network, it can go directly to it instead of going to the nearest point in the network. A navigation mesh can also be used by many types of agents of different sizes, rather than having many waypoint networks for agents of different sizes. Using a navigation mesh also speeds up graph exploration because, technically, a navigation mesh has fewer nodes than an equivalent waypoint network (that is, a network that has enough points to cover a navigation mesh). The navigation mesh Graph To summarize, a navigation mesh is a mesh that represents where an NPC can walk. A navigation mesh contains convex polygonal nodes (called cells). Each cell can be connected to each other using connections defined by an edge shared between them (or portal edge). In a navigation mesh, each cell can contain information about itself. For example, a cell may be labeled as toxic, and therefore only those units capable of resisting this toxicity can move across it. Personally, because of my experience, I view navigation meshes like the ones found in most Source games. However, all cells in Source's navigation meshes are rectangular. Our implementation is more flexible because the cells can be irregular polygons (as long as they're convex). Navigation Meshes In practice A navigation mesh implementation is actually three algorithms : A graph navigation algorithm A string pulling algorithm And a steering/path-smoothing algorithm In our cases, we used A*, the simple stupid funnel algorithm and a traditional steering algorithm that is still in development. Finding our cells Before doing any graph searches, we need to find 2 things : Our starting cell Our destination cell For example, let's use this navigation mesh : In this navigation meshes, every edge that are shared between 2 cells are also portal edges, which will be used by the string pulling algorithm later on. Also, let's use these points as our starting and destination points: Where our buddy (let's name it Buddy) stands is our staring point, while the flag represents our destination. Because we already have our starting point and our destination point, we just need to check which cell is closest to each point using an octree. Once we know our nearest cells, we must project the starting and destination points onto their respective closest cells. In practice, we do a simple projection of both our starting and destination points onto the normal of their respective cells. Before snapping a projected point, we must first know if the said projected point is outside its cell by finding the difference between the area of the cell and the sum of the areas of the triangles formed by that point and each edge of the cell. If the latter is remarkably larger than the first, the point is outside its cell. The snapping then simply consists of interpolating between the vertices of the edge of the cell closest to the projected point. In terms of code, we do this: Vector3f lineToPoint = pointToProject.subtract(start); Vector3f line = end.subtract(start); Vector3f returnedVector3f = new Vector3f().interpolateLocal(start, end, lineToPoint.dot(line) / line.dot(line)); In our example, the starting and destination cells are C1 and C8 respectively: Graph Search Algorithm A navigation mesh is actually a 2D grid of an unknown or infinite size. In a 3D game, it is common to represent a navigation mesh graph as a graph of flat polygons that aren't orthogonal to each other. There are games that use 3D navigation meshes, like games that use flying AI, but in our case it's a simple grid. For this reason, the use of the A* algorithm is probably the right solution. We chose A* because it's the most generic and flexible algorithm. Technically, we still do not know how our navigation mesh will be used, so going with something more generic can have its benefits... A* works by assigning a cost and a heuristic to a cell. The closer the cell is to our destination, the less expensive it is. The heuristic is calculated similarly but we also take into account the heuristics of the previous cell. This means that the longer a path is, the greater the resulting heuristic will be, and it becomes more likely that this path is not an optimal one. We begin the algorithm by traversing through the connections each of the neighboring cells of the current cell until we arrive at the end cell, doing a sort of exploration / filling. Each cell begins with an infinite heuristic but, as we explore the mesh, it's updated according to the information we learn. In the beginning, our starting cell gets a cost and a heuristic of 0 because the agent is already inside of it. We keep a queue in descending order of cells based on their heuristics. This means that the next cell to use as the current cell is the best candidate for an optimal path. When a cell is being processed, it is removed from that queue in another one that contains the closed cells. While continuing to explore, we also keep a reference of the connection used to move from the current cell to its neighbor. This will be useful later. We do it until we end up in the destination cell. Then, we "reel" up to our starting cell and save each cell we landed on, which gives an optimal path. A* is a very popular algorithm and the pseudocode can easily be found. Even Wikipedia has a pseudocode that is easy to understand. In our example, we find that this is our path: And here are highlighted (in pink) the traversed connections: The String Pulling Algorithm String pulling is the next step in the navigation mesh algorithm. Now that we have a queue of cells that describes an optimal path, we have to find a queue of points that an AI agent can travel to. This is where the sting pulling is needed. String pulling is in fact not linked to characters at all : it is rather a metaphor. Imagine a cross. Let's say that you wrap a silk thread around this cross and you put tension on it. You will find that the string does not follow the inner corner of it, but rather go from corner to corner of each point of the cross. This is precisely what we're doing but with a string that goes from one point to another. There are many different algorithms that lets us to do this. We chose the Simple Stupid Funnel algorithm because it's actually... ...stupidly simple. To put it simply (no puns intended), we create a funnel that checks each time if the next point is in the funnel or not. The funnel is composed of 3 points: a central apex, a left point (called left apex) and a right point (called right apex). At the beginning, the tested point is on the right side, then we alternate to the left and so on until we reach our point of destination. (as if we were walking) When a point is in the funnel, we continue the algorithm with the other side. If the point is outside the funnel, depending on which side the tested point belongs to, we take the apex from the other side of the funnel and add it to a list of final waypoints. The algorithm is working correctly most of the time. However, the algorithm had a bug that add the last point twice if none of the vertices of the last connection before the destination point were added to the list of final waypoints. We just added an if at the moment but we could come back later to optimize it. In our case, the funnel algorithm gives this path: The Steering Algoritm Now that we have a list of waypoints, we can finally just run our character at every point. But if there were walls in our geometry, then Buddy would run right into a corner wall. He won't be able to reach his destination because he isn't small enough to avoid the corner walls. That's the role of the steering algorithm. Our algorithm is still in heavy development, but its main gist is that we check if the next position of the agent is not in the navigation meshes. If that's the case, then we change its direction so that the agent doesn't hit the wall like an idiot. There is also a path curving algorithm, but it's still too early to know if we'll use that at all... We relied on this good document to program the steering algorithm. It's a 1999 document, but it's still interesting ... With the steering algoritm, we make sure that Buddy moves safely to his destination. (Look how proud he is!) So, this is the navigation mesh algorithm. I must say that, throughout my research, there weren't much pseudocode or code that described the algorithm as a whole. Only then did we realize that what people called "Navmesh" was actually a collage of algorithms rather than a single monolithic one. We also tried to have a cyclic grid with orthogonal cells (i.e. cells on the wall, ceiling) but it looked like that A* wasn't intended to be used in a 3D environment with flat orthogonal cells. My hypothesis is that we need 3D cells for this kind of navigation mesh, otherwise the heuristic value of each cell can change depending on the actual 3D length between the center of a flat cell and the destination point. So we reduced the scope of our navigation meshes and we were able to move an AI agent in our organic dungeon. Here's a picture : Each cyan cubes are the final waypoints found by the String pulling and blue lines represents collisions meshes. Our AI is currently still walking into walls, but the steering is still being implemented. 0 comments 6. As DMarket platform development continues, we would like to share a few case studies regarding the newest functionality on the platform. With these case studies we would like to illuminate our development process, user requirements gathering and analysis, and much more. The first case study we’re going to share is “DMarket Wallet Development”: how, when and why we decided to implement functionality which improved virtual items and DMarket Coins collection and transfer. DMarket cares about every user, no matter how big or small the user group is. And that’s why we recently updated our virtual item purchase rules, bringing a brand new “DMarket Wallet” feature to our users. So let’s take a retrospective look and find out what challenges were brought to the DMarket team within this feature and how these challenges were met. DMarket and Blockchain Virtual Items Trading Rules Within the first major release of the DMarket platform, we provided you with a wide range of possibilities and options, assuring Steam account connection within user profile, confirmation of account and device ownership via email for enhanced security, DMarket Coins, and DMarket Tokens exchanging, transactions with intermediaries on blockchain within our very own Blockchain system called “Blockchain Explorer”. And well, regarding Blockchain... While it has totally proved itself as a working solution, we were having some issues with malefactors, as many of you may already know. DMarket specialists conducted an investigation, which resulted in a perfect solution: we found out that a few users created bots to buy our Founder’s Mark, a limited special edition memorabilia to commemorate the launch of the platform, for lower prices and then sell them at higher prices. Sure thing, there was no chance left for regular users. A month ago we fixed the issue, to our great relief. We received real feedback from the community, a real proof-of-concept. The whole DMarket ecosystem turned out to be truly resilient, proving all our detractors wrong. And while we’ve got proof, we also studied how users feel about platform UX since blockchain requires additional efforts when buying or selling an item. With our first release of the Demo platform, we let users sign transactions with a private key from their wallet. In terms of user experience, that practice wasn’t too good. Just think about it: you should enter the private key each time you want to buy or sell something. Every transaction required a lot of actions from the user’s side, which is unacceptable for a great and user-friendly product like ours. That’s why we decided to move from that approach, and create a single unified “wallet” on the DMarket side in order to store all the DMarket Coins and virtual items on our side and let users buy or sell stuff with a few clicks instead of the previous lengthy process. In other words, every user received a public key which serves as a destination address, while private keys were held on the DMarket side in order to avoid transaction signing each time something is traded. This improved usability, and most of our users were satisfied with the update. But not all of them... You Can’t Make Everyone Happy….. Can You? By removing the transaction signing requirement we made most of our users happy. Of course, within a large number of happy people, we can always find those who are worried about owning a public key wallet. When you don’t own a public key, it may disturb you a little bit. Sure, DMarket is a trusted company, but there are people who can’t trust even themselves sometimes. So what were we gonna do? Ignore them? Roll back to the previous way of buying virtual items and coins? No! We decided to go the other way. Within the briefest timeline, the DMarket team decided on providing a completely new feature on Blockchain Explorer — wallet creation functionality. With this functionality, you can create a wallet with 2 clicks, getting both private and public keys and therefore ensuring your items’ and coins’ safety. Basically, we separated wallets on the marketplace and wallets on our Blockchain in order to keep great UX and reassure a small part of users with a needed option to keep everything in a separate wallet. You can go shopping on DMarket with no additional effort of signing every transaction, and at the same time, you are free to transfer all the goods to your very own wallet anytime you feel the need. Isn’t it cool? Outcome After implementation of a separate DMarket wallet creation feature, we killed two birds with one stone and made everyone satisfied. Though it wasn’t too easy since we had a very limited amount of time. So if you need it, you can try it. Moreover, the creation of DMarket wallet within Blockchain Explorer will let you manage your wallet even on mobile devices because with downloading private and public keys you also get a 12-word mnemonic phrase to restore your wallet on any mobile device, from smartphone to tablet. Wow, but that’s another story — a story about DMarket Wallet application which has recently become available for Android users in the Google Play. Stay tuned for more case studies and don't forget to check out our website and gain firsthand experience with in-game items trading! 0 comments 7. I got into a conversation awhile ago with some fellow game artists and the prospect of signing bonuses got brought up. Out of the group, I was the only one who had negotiated any sort of sign on bonus or payment above and beyond base compensation. My goal with this article and possibly others is to inform and motivate other artists to work on this aspect of their “portfolio” and start treating their career as a business. What is a Sign-On Bonus? Quite simply, a sign-on bonus is a sum of money offered to a prospective candidate in order to get them to join. It is quite common in other industries but rarely seen in the games unless it is at the executive level. Unfortunately, conversations centered around artist employment usually stops at base compensation, quite literally leaving money on the table. Why Ask for a Sign-On Bonus? There are many reasons to ask for a sign-on bonus. In my experience, it has been to compensate for some delta between how much I need vs. how much the company is offering. For example, a company has offered a candidate a position paying$50k/year. However, research indicates that the candidate requires $60k/year in order to keep in line with their personal financial requirements and long-term goals. Instead of turning down the offer wholesale, they may ask for a$10k sign on bonus with actionable terms to partially bridge the gap. Whatever the reason may be, the ask needs to be reasonable. Would you like a $100k sign-on bonus? Of course! Should you ask for it? Probably not. A sign-on bonus is a tool to reduce risk, not a tool to help you buy a shiny new sports car. Aspects to Consider Before one goes and asks for a huge sum of money, there are some aspects of sign-on bonus negotiations the candidate needs to keep in mind. - The more experience you have, the more leverage you have to negotiate - You must have confidence in your role as an employee. - You must have done your research. This includes knowing your personal financial goals and how the prospective offer changes, influences or diminishes those goals. To the first point, the more experience one has, the better. If the candidate is a junior employee (roughly defined as less than 3 years of industry experience) or looking for their first job in the industry, it is highly unlikely that a company will entertain a conversation about sign-on bonuses. Getting into the industry is highly competitive and there is likely very little motivation for a company to pay a sign-on bonus for one candidate when there a dozens (or hundreds in some cases) of other candidates that will jump at the first offer. Additionally, the candidate must have confidence in succeeding at the desired role in the company. They have to know that they can handle the day to day responsibilities as well as any extra demands that may come up during production. The company needs to be convinced of their ability to be a team player and, as a result, is willing to put a little extra money down to hire them. In other words, the candidate needs to reduce the company’s risk in hiring them enough that an extra payment or two is negligible. And finally, they must know where they sit financially and where they want to be in the short-, mid-, and long-term. Having this information at hand is essential to the negotiation process. The Role Risk Plays in Employment The interviewing process is a tricky one for all parties involved and it revolves around the idea of risk. Is this candidate low-risk or high-risk? The risk level depends on a number of factors: portfolio quality, experience, soft skills, etc. Were you late for the interview? Your risk to the company just went up. Did you bring additional portfolio materials that were not online? Your risk just went down and you became more hireable. If a candidate has an offer in hand, then the company sees enough potential to get a return on their investment with as little risk as possible. At this point, the company is confident in their ability as an employee (ie. low risk) and they are willing to give them money in return for that ability. Asking for the Sign-On Bonus So what now? The candidate has gone through the interview process, the company has offered them a position and base compensation. Unfortunately, the offer falls below expectations. Here is where the knowledge and research of the position and personal financial goals comes in. The candidate has to know what their thresholds and limits are. If they ask for$60k/year and the company is offering $50k, how do you ask for the bonus? Once again, it comes down to risk. Here is the point to remember: risk is not one-sided. The candidate takes on risk by changing companies as well. The candidate has to leverage the sign-on bonus as a way to reduce risk for both parties. Here is the important part: A sign-on bonus reduces the company’s risk because they are not commiting to an increased salary and bonus payouts can be staggered and have terms attached to them. The sign-on bonus reduces the candidate’s risk because it bridges the gap between the offered compensation and their personal financial requirements. If the sign-on bonus is reasonable and the company has the finances (explained further down below), it is a win-win for both parties and hopefully the beginning a profitable business relationship. A Bit about Finances First off, I am not a business accountant nor have I managed finances for a business. I am sure that it is much more complicated than my example below and there are a lot of considerations to take into account. In my experience, however, I do know that base compensation (ie. salary) will generally fall into a different line item category on the financial books than a bonus payout. When companies determine how many open spots they have, it is usually done by department with inter-departmental salary caps. For a simplified example, an environment department’s total salary cap is$500k/year. They have 9 artists being paid $50k/year, leaving$50k/year remaining for the 10th member of the team. Remember the example I gave earlier asking for $60k/year? The company cannot offer that salary because it breaks the departmental cap. However, since bonuses typically do not affect departmental caps, the company can pull from a different pool of money without increasing their risk by committing to a higher salary. Sweetening the Deal Coming right out of the gate and asking for an upfront payment might be too aggressive of a play (ie. high risk for the company). One way around this is to attach terms to the bonus. What does this mean? Take the situation above. A candidate has an offer for$50k/year but would like a bit more. If through the course of discussing compensation they get the sense that $10k is too high, they can offer to break up the payments based on terms. For example, a counterpoint to the initial base compensation offer could look like this:$50k/year salary $5k bonus payout #1 after 30 days of successful employment$5k bonus payout #2 after 365 days (or any length of time) of successful employment In this example, the candidate is guaranteed $55k/year salary for 2 years. If they factor in a standard 3% cost of living raise, the first 3 years of employment looks like this: Year 0-1 =$55,000 ($50,000 +$5,000 payout #1) Year 1-2 = $56,500 (($50,000 x 1.03%) + $5,000 payout #2) Year 2-3 =$53,045 ($51,500 x 1.03%) Now it might not be the$60k/year they had in mind but it is a great compromise to keep both parties comfortable. If the Company Says Yes Great news! The company said yes! What now? Personally, I always request at least a full 24 hours to crunch the final numbers. In the past, I’ve requested up to a week for full consideration. Even if you know you will say yes, doing due diligence with your finances one last time is always a good practice. Plug the numbers into a spreadsheet, look at your bills and expenses again, and review the whole offer (base compensation, bonus, time off/sick leave, medical/dental/vision, etc.). Discuss the offer with your significant other as well. You will see the offer in a different light when you wake up, so make sure you are not rushing into a situation you will regret. If the Company Say No If the company says no, then you have a difficult decision to make. Request time to review the offer and crunch the numbers. If it is a lateral move (same position, different company) then you have to ask if the switch is worth it. Only due diligence will offer that insight and you have to give yourself enough time to let those insights arrive. You might find yourself accepting the new position due to other non-financial reasons (which could be a whole separate article!). Conclusion/Final Thoughts  When it comes to negotiating during the interview process, it is very easy to take what you can get and run. You might fear that in asking for more, you will be disqualifying yourself from the position. Keep in mind that the offer has already been extended to you and a company will not rescind their offer simply because you came back with a counterpoint. Negotiations are expected at this stage and by putting forth a creative compromise, your first impression is that of someone who conducts themselves in a professional manner. Also keep in mind that negotiations do not always go well. There are countless factors that influence whether or not someone gets a sign-on bonus. Sometimes it all comes down to being there at the right time at the right place. Just make sure you do your due diligence and be ready when the opportunity presents itself. Hope this helps!
By RyRyB

Any currently open scene is what you are working on. In Unity 2017, you can load more scenes into the hierarchy while editing, and even at runtime, through the new SceneManager API, where two or more scenes can be worked on simultaneously. Scenes can be manipulated and constructed by using the Hierarchy and Scene views. OK, now that we know what assets and scenes let’s start setting up a scene and building a game asset. Setting up a scene and preparing game assets Create a new scene from the main menu by navigating to Assets | Create | Scene, and name it ParallaxGame. In this new scene, we will set up, step by step, all the elements for our 2D game prototype. First of all, we will switch the camera setting in the Scene view to 2D by clicking on the button as shown by the red arrow in the following screenshot: As you can see, now the Scene view camera is orthographic. You can't rotate it as you wish, as you can do with the 3D camera. Of course, we will want to change this setting on our Main Camera as well. Also, we want to change the Orthographic size to 4.5 to have the correct view of the scene. Instead, for the Skybox, we will choose a very dark or black color as clear color in the depth setting. This is how the Inspector should look when these settings are done:   While the Clipping Planes distances are important for setting the size of the frustum cone of a 3D, for the Perspective camera (inside which everything will be rendered by the engine), we should only set the Orthographic Size to 4.5, to have the correct distance of the 2D camera from the scene. When these settings are done, proceed by importing Chapter2-3-4.unitypackage into the project. You can either double-click on the package file with Unity open, or use the top menu: Assets | Import | Custom Package. If you haven't imported all the materials from the book's code already, be sure to include the Sprites subfolder. After the import, look in the Sprites/Parallax/DarkCave folder in the Project view and you will find some images imported as textures (as per default). The first thing we want to do now is to change the import settings of these images, in the Inspector, from Texture to Sprite (2D and UI). To do so, select all the images in the Project view in the Sprites/Parallax/DarkCave folder, all except the _reference_main_post file. Which is just a picture used as a reference of what the game level should look like: The Import Settings shown in the Inspector after selecting the seven images in the Project view The Max Size setting is hidden (-) because we have a multi-selection of image files. After having made the multiple selections, again, in the Inspector, we will do the following: Set the Texture Type option to Sprites (2D and UI). By default, images are imported as textures; to import them as Sprites, this type must be set. Uncheck the Generate Mip Maps option as we don't need MIP maps for this project as we are not going to look at the Sprites from a distant point of view, for example, games with the zoom-in/zoom-out feature (like the original Grand Theft Auto 2D game) would need this setting checked. Set Max Size to the maximum allowed. To ensure that you import all the images at their maximum resolution, set this to 8192. This is the maximum resolution size for an image on a modern PC, imported as a Sprite or texture. We set it so high because most of the background images we have in the collection are around 6,000 pixels wide. Click on the Apply button to apply these changes to all the images that were selected: The Project view showing the content of the folder after the images have been set to Sprite in the Import Settings. Placing the prefabs in the game Unity can place the prefabs in the game in many ways, the usual, visual method is to drag a stored prefab or another kind of file/object directly into the scene. Before dragging in the Sprites we imported, we will create an empty GameObject and rename it ParallaxCave. We will drag the layer images we just imported as Sprites, one by one, from the Project view (pointing at the Assets/Chapters2-3-4/Sprites/Background/DarkCave folder) into the Scene view, or more simply, directly in the Hierarchy view as the children of our ParallaxCaveGameObject, resulting in a scene Hierarchy like the one illustrated here: You can't drag all of them instantly because Unity will prompt you to save an animation filename for the selected collection of Sprites; we will see this later for our character and for the collectable graphics. Importing and placing background layers In any game engine, 2D elements, such as Sprites, are rendered following a sort order; this order is also called the z-order because it is a way to express the depth or to cope with the missing z axis in a two-dimensional context. The sort order is assigned an integer number which can be positive or negative; 0 is the middle point of this draw order. Ideally, a sort order of zero expresses the middle ground, where the player will act, or near its layer. Look at this image: Image courtesy of Wikipedia: parallax scrolling   All positive numbers will render the Sprite element in front of the other elements with a lower number. The graphic set we are going to use was taken from the Open Game Art website at http://opengameart.org. For simplicity, the provided background image files are named with a number within parentheses, for example, middleground(z1), which means that this image should be rendered with a z sort order of 1. Change the sort order property of the Sprite component on each child object under ParallaxCave according to the value in the parentheses at the end of their filenames. This will rearrange the graphics into the appropriately sorted order. After we place and set the correct layer order for all the images, we should arrange and scale the layers in a proper manner to end as something like the reference image furnished in the Assets/Chapters2-3-4/Sprites/Background/DarkCave/ folder. You can take a look at the final result for this part anytime, by saving the current scene and loading the Chapter3_start.unity scene. You just read an excerpt from the book, Unity 2017 Game Development Essentials - Third Edition written by Tommaso Lintrami and published by Packt Publishing. Use the code ORGDA10 at checkout to get recommended eBook retail price for $10 only until April 30, 2018. 0 comments By khawk 11. This reference guide has now been proofread by @stimarco (Sean Timarco Baggaley). Please give your thanks to him. The guide should now be far easier to read and understand than previous revisions, enjoy! Note: The normal mapping tutorial has been temporarily moved, to be added back as its own topic, to help separate the two for more clarity. If anyone has any corrections, please contact me. 3D Graphics Primer 1: Textures. This is a quick reference for artists who are starting out. The first topic revolves around textures and the many things an artist who is starting out needs to understand. I am primarily a 3d artist and my focus will therefore be primarily on 3d art. However, some of this information is applicable to 2d artists. Textures What is a texture? By classical definition a texture is the visual and esp. tactile quality of a surface (Dictionary.com). Since current games lack the ability to convey tactile sensations, a texture in game terms simply refers to the visual quality of a surface, with an implicit tactile quality. That is, a rock texture should give the impression of the surface of a rock, and depending on the type, a rough or smooth tactile quality. We see these types of surfaces in real life and feel them in real life. So when we see the texture, we know what it feels like without needing to touch it due to our past experiences. But a lot more goes into making a convincing texture beyond the simple tactile quality. As you will learn as you read on, textures in games is a very complex topic, with many elements involved in creating them for realtime rendering. We will look at: Texture File Types & Formats Texture Image Size Texture File Size Texture Types Tiling Textures Texture Bit Depth Making Normal Maps (Brief overview only) Pixel Density and Fill Rate Limitation Mipmaps Further Reading Further Reading Creating and using textures is such a big subject that covering it entirely within this one primer is simply not sensible. All I can sensibly achieve here is a skimming over the surface, so here are some links to further reading matter. Beautiful Yet Friendly - Written by Guillaume Provost, hosted by Adam Bromell. This is a very interesting article that goes into some depth about basic optimizations and the thought process when designing and modeling a level. It goes into the technical side of things to truly give you an understanding on what is going on in the background. You can use the information in this article to find out how to build models that use fewer resources -- polygons, textures, etc. -- for the same results. This is the reason why this is the first article I am linking to: it is imperative to understand the topics discussed in this article. If you need any extra explanation after reading it, you can PM me and I am more than happy to help. However, parts of this article go outside the texture realm of things and into the mesh side, so keep that in mind if you're focusing on learning textures at the moment. UVW Mapping Tutorial - by Waylon Brinck. This is about the best tutorial I have found for a topic that gives all 3D artists a headache: unwrapping your three-dimensional object into a two-dimensional plane for 2D painting. It is the process by which all 3D artists place a texture on a mesh (model). NOTE: while this tutorial is very good and will help you in learning the process, UVW mapping/unwrapping is just one of those things you must practice and experiment with for a while before you truly understand it. Poop In My Mouth's Tutorials - By Ben Mathis. Probably the only professional I know who has such a scary website name, but don't be afraid! I swear there is nothing terrible beyond that link. He has a ton of excellent tutorials, short and long, that cover both the modeling and texturing processes, ranging from normal-mapping to UVW unwrapping. You may want to read this reference first before delving into some of his tutorials. Texture File Types & Formats In the computer world, textures are really nothing more than image files applied to a model. Because of this, a variety of common computer image formats can be used. These include, .TGA, .DDS, .BMP, and even .JPG (or .JPEG). Almost any digital image format can be used, but some things must be taken into consideration: In the modern world of gaming, being heavily reliant on shaders, formats like the .JPG format are rarely used. This is because .JPG, and others like it, are lossy formats, where data in the image file is actually thrown away to make the file smaller. This process can result in compression artifacts The problem is that these artifacts will interfere with shaders, because these rely on having all the data contained within the image intact. Because of this, lossless formats are used -- formats like .DDS (if lossless option chosen), .BMP, and .TGA. However, there is such a thing called S3TC (also known as "dxt") compression. This was a compression technique developed for use on Savage 3D graphics cards, with the benefit of keeping a texture compressed within video memory whereas non-S3TC-compressed textures are not. This results in a 1:8 or greater compression ratio and can allow either more textures to be used in a scene, or can be used to increase the resolution of a texture without using more memory. S3TC compression can be made to work with any format, but is most commonly associated with the .DDS format. Just like the .jpg and other lossy formats, any texture using S3TC will suffer compression artifacts, and as such is not suitable for normal maps, (which we'll discuss a little later on). Even with S3TC it is common to use a lossless format for the texture format, and then apply S3TC when necessary. This is done to provide an artist with the ability to have lossless textures when needed -- e.g. for normal maps -- but then provide them with a method for compression on textures that could benefit from S3TC compression, such as diffuse textures. Texture Image Size The engineers who design computers and their component parts like us to feed data to their hardware in chunks that have dimensions defined as powers of two. (E.g. 16 pixels, 32 pixels, 64 pixels, and so on.) While it is possible to have a texture that is not the power of two, it is generally a good idea to stick to power-of-two sizes for compatibility reasons (especially if you're targeting older hardware). That is, if you're creating a texture for a game, you want to use image dimensions that are the power of two. Examples, 32x32, 16x32, 2048x1024, 1024x1024, 512x512, 512x32, etc. Say for example, you have a mesh/model and you're UV Unwrapping, for a game you must work within dimensions that are a power of two. Powers of two include: 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, and so on. What if you want to use images that aren't powers of two? In such cases, you can often use uneven pixel ratios. This means you can create your texture at, say, 1024x768, and then you can save it as 1024x1024. When you're applying your texture to your mesh you can stretch it back out in proportion. However, it is best to go for a 1:1 pixel ratio and create the texture starting at the power of 2, but the stretching is one method for getting around this if needed Please refer to the "Pixel Density and Fill Rate Limitation" section for more in depth info on how exactly to choose your image size. Texture File Size File size is important for a number of reasons. The file is the actual amount of memory (permanent or temporary) that the texture requires. For an obvious example, an uncompressed .BMP could be 6MB, this is the space it requires to be saved on a hard drive and within the video and/or system RAM. Using compression we can squeeze the same image into a file size of, say, 400 KB, or possibly even smaller. Compression, like that used by .JPG and other similar formats, will only do compression on permanent storage media, such as hard drives. That is to say, when the image is stored in video card memory it must be uncompressed within the memory, so you truly only get a benefit on storing the texture on its permanent medium but not in memory during use. Enter S3TC The key benefit of the S3TC compression system is that it compresses on hard drives, discs, and other media, while also staying compressed within video card memory. But why should you care what size it is within the video memory? Video cards have onboard memory called, unsuprisingly enough, video memory, for storing data that needs to be accessed fast. This memory is limited, so considerations on the artists' part must be used. The good news is that video card manufacturers are constantly adding more of this video memory -- known as Video RAM (or VRAM for short). Where once 64 MB was considered good, we can now find video cards with up to 1 GB of RAM. The more textures you have, the more RAM will be used. The actual amount is based primarily on the file size of each texture. Other data take up video memory, such as the model data itself, but the majority is used for textures. For this reason, it is a good idea to both plan your video memory usage and test how much you're using once in the engine. It is also advised that you have a minimum hardware configuration for what you want your game to run on. If this is the case, then you should always make sure your video memory usage does not go over the minimum target hardware's amount. Another advantage of in-memory compression like S3TC is that it can increase available bandwidth. If you know your engine on your target hardware may be swapping textures back and forth frequently (something that should be avoided if possible, but is a technique used on consoles), then you may want to consider having the textures compressed and then decompress them on the fly. That is to say, you have the textures compressed, and then when they're required, they're transported and then decompressed as they're added to video memory. This results in less data having to be shunted across the graphics card's bus (transport line) to and from the computer's main memory, resulting in less bandwidth utilization, but with the added penalty of a few wasted processing clocks. Texture Types Now we're going to discuss such things are diffuse, normal, specular, parallax and cube mapping. Aside from the diffuse map, these mapping types are common in what have become known as 'next-gen' engines, where the artist is given more control over how the model is rendered by use of control maps for shaders. Diffuse maps are textures which simply provide the color and any baked-in details. Games before shaders simply used diffuse textures. (You could say this is the 'default' texture type.) For example, when texturing a rock, the diffuse map of the rock would be just the color and data of that rock. Diffuse textures can be painted by hand or made from photographs, or a mixture of both. However, in any modern engine, most lighting and shadow detail is preferred to not be 'baked' (i.e. pre-drawn directly into the texture) into the diffuse map, but instead to have just the color data in the diffuse and use other control maps to recreate such things as shadows, specular reflections, refraction effects and so on. This results in a more dynamic look for the texture overall, helping its believability once in-game. 'Baking' such details will hinder the game engine's ability to produce "dynamic" results, which will cause the end result to look unrealistic. There is sometimes an exception to this rule: if you're providing "general" shading/lighting like ambient occlusion maps baked (merged) into the diffuse, then it is ok. These types of additions into the diffuse are general enough that they won't hinder the dynamic effect of running in a realtime engine, while achieving a higher level of realism. Another point to remember is that while textures sourced from photographs tend to work very well in 3D environment work, it is often frowned upon to use such 'photosourced textures' for humans. Human diffuse textures are usually hand-painted. Normal maps are used to provide lighting detail for dynamic lighting, however this is involved in an even more important role, as we will discuss shortly. Normal maps get their name from the fact that they recreate normals on a mesh using a texture. A 'normal' is a point (actually a vector) extending from a triangle on a mesh. This tells the game engine how much light the triangle should receive from a particular light source -- the engine simply compares the angle of the normal with the position and angle of the light itself and thus calculates how the light strikes the triangle. Without a normal map, the game engine can only use the data available in the mesh itself; a triangle would only have three normals for the engine to use -- one at each point -- regardless of how big that triangle is on the screen, resulting in a flat look. A normal map, on the other hand, creates normals right across a mesh's surface. The result is the capability to generate a normal map from a 2 million poly mesh and have this lighting detail recreated on a 200 poly mesh. This can allow an artist to recreate a high-poly mesh with relatively low polygons in comparison. Such tricks are associated with 'next-gen' engines, and are heavily used in screenshots of the Unreal 3 Engine, where you can see large amounts of detail yet able to run in realtime due to the actual amount of polys used. Normal maps use the different color channels (red, green, and blue) for storing gray scale data of lighting information at different angles, however there is no set standard for how these channels can be interpreted and as such sometimes require a channel to be flipped for correct function in an engine. Normal maps can be generated from high-poly meshes, or they can be image generated, that is, being generated from a gray scale map. However, high-poly generated normal maps tend to be preferred as they tend to have more depth. This is for various reasons, but the main one is that it is difficult for most to paint a grayscale map that is equal to the quality you'll receive straight from a model. Also, you will often find that the image generators tend to miss details, requiring the artist to edit the normal map by hand later. However, it is not impossible to receive near equal results using both methods, each have their own requirements, it is up to you on which to use in each situation (Please refer to the tutorial section for extended information on normal maps.) Specular maps are simple in creation. They are easy to paint by hand, because the map is simply a gray scale map that defines the specular level for any point on a mesh. However, in some engines and in 3D modeling applications this map can be full-color so the brightness defines the specular level and color defines the color of the specular highlights. This gives the artist finer control to produce more lifelike textures because the specific specular attribute of certain materials can be more defined and closer to reality. In this way you can give a plastic material a more plastic-like specular reflection, or simulate a stone's particular specular look. Parallax mapping picks up where regular normal mapping fails. We create normals on a model by use of a normal map. A parallax map does the same thing as a normal map except it samples a grayscale map within the alpha channel. Parallax mapping works by using the angles recorded in the tangent space normal maps along with the heightmap to calculate which way to displace the texture coordinates. It uses the grayscale map to define how much the texture should be extruded outwards, and uses the angle information recorded in the tangent normal map to determine the angle to offset the texture. Doing things this way a parallax map can then recreate the extrusion of a normal map, but without the flattening that visible in ordinary normal mapping due to lack of data at different perspectives. It mainly gets its name from how the effect is created by the parallax effect. The end results are cleaner and deeper extrusions with less flattening that occurs in normal mapping because the texture coordinates are offset with your perspective. Parallax mapping is usually more costly than normal mapping. Parallax also has the limitation of not being used on deformable meshes because of the tendency for the texture to "swim" due to the way textures are offset. Cube mapping uses a texture that is not unlike an unfolded box and acts just like a sky box when used. Basically this texture is designed like an unfolded box where it all is folded back together when being used. This allows us to create a 3d dimensional reflection of sorts. The result is very realistic precomputed reflections. For example, you would use this technique to create a shiny, metal ball. The cube map would provide the reflection data. (In some engines, you can tell the engine itself to generate a cube map from a specific point in the scene and have it apply the result to a model. This is how we get shiny, reflective cars in racing games, for example. The engine is constantly taking cube map 'photos' for each car to ensure it reflects its surroundings accurately.) Tiling Textures Now, while you can have unique, specific textures made for specific models, a common thing to do to both save time and video memory, is tiling textures. These are textures which can be fitted together like floor or wall tiles, producing a single, seamless texture/image. The benefit is that you can texture an entire floor in an entire building using a single tiling texture, which both saves the artist's time, and video memory due to fewer textures being needed. A tiling texture is achieved by having the left and right side of a texture blend into each other, and the same for the bottom and top of the texture. Such blending can be achieved by the use of a specialist program, a plugin, or by simply offsetting the texture a little to the left and down, cleaning up the seams, and then offsetting back to the original position After you create your first tiling texture and test it, you're bound to see that each texture will produce a 'tiling artifact' which shows how and where the texture is tiled. Such artifacts can be reduced by avoiding high-contrast detail, unique detail (such as a single rock on a sand texture), and by tiling the texture less. Texture Bit Depth A texture is just an image file. This means most of the theory you're familiar with when it comes to working with images also applies to textures. One such would be bit depth. Here you will see such numbers as 8, 16, 24, and 32 bits. These each correspond to the amount of color data that is stored for each image. How do we get the number 24 from an image file? Well, the number 24 refers to how many bits it contains. That is, that you have 3 channels, red, green, and blue, all of which are simply channels which contain a gray scale image, but are added together to produce a full color image. So black, in the red channel, means "no red" at that point, while white in the red channel means "lots of red". Same applies to blue and green. When these are combined, they produce a full color image, a mix of Red, Green and Blue (if using the RGB color model). The bits come in by the fact that they define how many levels of gray each channel has: 8 bits per channel, over 3 channels, is 24 bits total. 8 bits gives you 256 levels of gray. Combining the idea that 8 bits gives you 256 levels of gray and that each channel is simply gray scale and different levels of gray define a level within that color, we can then see that a 24 bit image will give us 16,777,216 different colors to play with. That is, 8 bits x 3 channels= 24 bits, 8 bits= 256 gray scale levels, so 256 x 3= 16,777,216 colors. This knowledge comes in useful when at certain times it is easier to edit the RGB channels individually, with a correct understanding you can then delve deeper into editing your textures. However, with the increase in shader use, you'll often see a 32 bit image/texture file. These are image files which contain 4 channels, each of 8 bits: 4 x 8 = 32. This allows a developer to use the 4th channel to carry a unique control map or extra data needed for shaders. Since each channel is gray scale, a 32 bit image is ideal to carry a full color texture along with an extra map within it. Depending on your engine you may see a full color texture with the extra 4th channel being used to hold a gray scale map for transparency (more commonly known as an "alpha channel"), specular control map, or a gray scale map along with a normal map in the other channels to be used for parallax mapping. As you paint your textures you may start to realize that you're probably not using all of the colors available to you in a 24 bit image. And you're probably right, this is why artists can at times use a lower bit depth texture to achieve the same or near the same look with a lesser memory footprint. There are certain cases where you will more than likely need a 24 bit image however: If your image/texture contains frequent gradations in the color or shading, then a 24 bit image is required. However, if your image/texture contains solid colors, little detail, little or no shading, and so on, you can probably get away with a 16, 8, or perhaps even a 4 bit texture. Often, this type of memory conservation technique is best done when the artist is able to choose/make his own color pallette. This is where you hand pick the colors that will be saved with your image, instead of letting the computer automatically choose. By using a careful eye you have the possibility to choose more optimal colors which will fit your texture better. Basically, in a way, all you're doing is throwing out what would be considered useless colors which are being stored in the texture but not being used. Making Normal Maps There are two methods for creating normal maps: Using a detailed mesh/model. Creating a normal map from an image. The first method is part of a common workflow that nearly all modelers who support normal map generation use. For generating a normal map from a model you can either generate it out to a straight texture, or if you're generating your normal map from a high-poly mesh, it is common to then model the low poly mesh around your high-poly mesh. (Some artists have prefer for modeling the low-poly version first while others like to do the high then the low, in the end there is no perfect way, its just preference.) For example: you have a high-poly rock, you will then model/build a low poly mesh around the high, then UVW unwrap it, and generate the normal map from your high-poly version. Virtual "rays" will be cast from the high- to the low-poly model -- a technique known as "projecting". This allows for a better application of your high-poly mesh normal map to your low-poly mesh since you're projecting the detail from the high to the low. However, some applications will switch the requirements and have your low poly mesh be inside your high, and others allow the rays for generating the normal map to be cast both ways. So refer to your application tutorials for how to do this as it may vary. Creating a normal map from an image. This method can be quicker than the more common method described above. For this, all you need is an edited version of your diffuse map. The key to good-looking image-based normal maps is to edit out any unneeded information for your grayscale diffuse texture. If your diffuse has any baked-in specular, shadows, or any information that does not define depth, this needs to be removed from the image. Also, anything that is extra, like strips of paint on a concrete texture, that too should be edited out. This is because, just like bump maps, and displacement maps, the colour of the pixels defines depth, with lighter pixels being "higher" than darker pixels. So, if you have specular (will turn white when made gray), it will be interpreted as a bump in your normal map, you don't want this if the specular in fact lays on a flat surface. The same applies to shadows and everything else mentioned: it will all interfere with the normal map generation process. You simply want to only have various shades of gray represent various depths, any other data in the texture will not produce the correct results. For generating normal maps you can always use the Nvidia Plugin, however it takes a lot of tweaking to get a good looking normal map. As such, I recommend Crazy Bump!. Crazy Bump will produce some very good normal maps if the given texture it is generating it from is good. Combining the two methods. It is common, even if you're generating a normal map from a 3d high-poly mesh to then generate an image generated normal map and overlay it over the high-poly generated one. This is done by generating one from your diffuse map, filling the resulting normal map's blue channel with 128 neutral gray, and then overlaying this over your high-poly generated one. This is done to add in those small details that only the image can generate. This way you get the high frequency detail along with the nice and cleanly generated mid-to-low frequency detail from your high-poly generated normal map. Pixel Density and Fill Rate Limitation Let's say you have a coin that you just finished UVW unwrapping, it will indeed be very small once in-game, however you decide it would be fine to use a 1024x1024 texture. What is wrong with the above situation? Firstly, you shouldn't need to UVW unwrap a coin! Furthermore, you should not be applying the 1024x1024 texture! Not only is this wasteful of video memory, but it will result in uneven pixel density and will increase your fill rate on that model for no reason. A good rule of thumb is to only use the amount of resources that would make sense based on how much screen space an object will take up. A building will take up more of the screen than a coin, so it needs a higher resolution texture and more polygons. A coin takes up less screen space and therefore needs fewer polys and a lower resolution texture to obtain a similar pixel density. So, what is pixel density? It is the density of each pixel from a texture on a mesh. For example, take the UVW unwrapping tutorial linked to in the "Texture Image Size" section: There you will see a checkered pattern, this is not only used to make sure the texture is applied right, but to also keep track of pixel density. If you increased the pixel density, you would see the checkered pattern get more dense; if you decrease the density, the checkered pattern would be less dense, with fewer squares showing. Maintaining a consistent pixel density in a game helps all of the art fit together. How would you feel if your high pixel density character walks up to a wall with a significantly lower pixel density? Your eyes would be able to compare the two and see that the wall looks like crap compared to the character, however would this same thing happen if the character were near the same pixel density of the wall? Probably not -- such things only become apparent (within reason) to the end user if they have something to compare it to. If you keep a consistent pixel density throughout all of the game's assets, you will see all of it fits together better. It is important to note that there is one other reason for this, but we'll come to it in a moment. First, we need to look at two related problems that can arise: transform(ation) limited and fill-rate limited modeling. A transform-limited model will have less pixel density per polygon than a fill-rate limited model where it has a higher pixel density per polygon. The theory is that a model takes longer on either processing the polys, or processing the actual pixel-dense surface. Knowing this, we can see that our coin, with very few polys will have a giant pixel density per polygon, resulting in a fill rate limited mesh. However, it does not need to be fill rate limited if we lower the texture resolution, resulting in a lower pixel density. The point is that your mesh will be held back when rendering based on which process takes longer: transform or fill rate. If your mesh is fill rate limited then you can speed up its processing by decreasing its pixel density, and its speed will increase until you reach transform limitation, in which your mesh is now taking longer to render based on the amount of polygons it contains. In the latter case, you would then speed up the processing of the model by decreasing the amount of polygons the model contains. That is, until you decrease the polygon count to the point where you're now fill rate limited once again! As you can see, it's a balancing act. The trick is to maximize the speed of the transform and fill rate processing (minimize the impact of both as much as you can), to get the best possible processing speed for your mesh. That said, being fill rate limited can sometimes be a good thing. The majority of "next-gen" games are fill rate limited primarily because of their use of texture/shading techniques. So, if you can't possibly get any lower on the fill rate limitation and you're still fill rate limited, then you have a little bit of wiggle room to work around where you can actually introduce more polygons with no performance hit. However, you should always try to cut down on fill rate limitations when possible because of general performance concerns Some methods revolve around splitting up a single polygon into multiple polygons on a single mesh (like a wall for example). This works by then decreasing the pixel density and processing (shaders) for the single polygon by splitting the work into multiple polygons. There are other methods for dealing with fill rate limitation, but mainly it is as simple as keeping your pixel density at a reasonable level. MipMaps It is fitting that after we discuss pixel density and fill rate limitation that we discuss a thing called Mipmapping. Mipmaps (or mip maps) are a collection of precomputed lower resolution image copies for a texture contained in the texture. Let's say you have a 1024x1024 texture. If you generate mipmaps for your texture, it will contain the original 1024x1024 texture, but it will also contain a 512x512, 256x256, 128x128, 64x64, 32x32, 16x16, 8x8, 4x4, 2x2 version of the same texture, (exactly how many levels there are is up to you). These smaller mipmaps (textures) are then used in sequence, one after the other, according to the model's distance from the camera in the scene. If your model uses a 1024x1024 texture up close, it may be using a 256x256 texture when further away, and an even smaller mipmap texture level when it's way off in the distance. This is done because of many things: The further away you are from your mesh, the less polygonal and texture detail is needed. This is because all displays have a fixed display resolution and it is physically impossible for the player to decipher the detail of a 1024x1024 texture and 6,000 polygon mesh when the model takes up only 20 pixels on screen. The further away we are from the mesh, the fewer the polygons and the lower the texture resolution we need to render it. Because of the whole fill rate limitation described above, it is beneficial to use mipmaps as less texture detail must be processed for distant meshes. This results is a less fill-rate-heavy scene because only the closer models are receiving larger textures, whereas more distant models are receiving smaller textures. Texture filtering. What happens when the player tries to view a 1024x1024 texture at such a distance that only 40 pixels are given to render the mesh on screen? You get noise and aliasing artefacts! Without mipmaps, any textures too large for the display resolution will only result in unneeded and unwanted noise. Instead of filtering out this noise, mipmaps use a lower resolution texture for different distances, this results in less noise. It is important to note, that while mipmaps will increase performance overall, you're actually increasing your texture memory usage. The mipmaps and the whole texture will be loaded into memory. However, it is possible to have a system where the user or dev can select the highest mipmap they want and the ones higher than this limit will not be loaded into memory (as the system we're using now), however the mipmaps which meet or are lower than this limit will still be loaded into memory. It is widely agreed that the benefits of mipmaps vastly outweigh the small memory hit. NOTE: Mesh detail can also affect performance, so the equivalent method used for mesh detail is known as LOD -- "Level Of Detail. Multiple versions of the mesh itself are stored at different levels of detail. The less-detailed mesh is rendered when it's a long way away. Like mipmaps, a mesh can have any number of levels of detail you feel it requires. The image below is of a level I created which makes use of most of what we've discussed. It makes use of S3TC compressed textures, normal mapping, diffuse mapping, specular mapping, and tiled textures. 0 comments 12. Sounds This is our final part, 5 of a series on creating a game with the Orx Portable Game Engine. Part 1 is here, and part 4 is here. It's great that collecting the pickups work, but a silent game is pretty bland. It would be great to have a sound play whenever a pickup is collected. Start by configuring a sound: [PickupSound] Sound = pickup.ogg KeepInCache = true Then as part of the collision detection in the PhysicsEventHandler function, we change the code to be: if (orxString_SearchString(recipientName, "PickupObject") != orxNULL) { orxObject_SetLifeTime(pstRecipientObject, 0); orxObject_AddSound(pstSenderObject, "PickupSound"); } if (orxString_SearchString(senderName, "PickupObject") != orxNULL) { orxObject_SetLifeTime(pstSenderObject, 0); orxObject_AddSound(pstRecipientObject, "PickupSound"); } In code above, if the recipient is a pickup object, then use the orxObject_AddSound function to place our sound on the sender object. There's little point adding a sound to an object that is about to be deleted. And of course, if the pickup object is the sender, we add the sound to the recipient object. Also, the PickupSound that is added to the object, is the config section name we just defined in the config. Compile and run. Hit the pickups and a sound will play. You can also use sounds without code. There is an AppearSound section already available in the config. We can use this sound on the ufo when it first appears in the game. This is as simple as adding a SoundList property to the ufo: [UfoObject] Graphic = UfoGraphic Position = (0, 0, -0.1) Body = UfoBody AngularVelocity = 200 SoundList = SoundAppear Re-run and a nice sound plays at the start of the game. Adding a score What's a game without a score? We need to earn points for every pickup that is collected. The great thing about Orx objects is that they don't have to contain a texture as a graphic. They can contain a font and text rendered to a graphic instead. This is perfect for making a score object. Start by adding some config for the ScoreObject: [ScoreObject] Graphic = ScoreTextGraphic Position = (-380, -280, 0) Next, to add the ScoreTextGraphic section, which will not be a texture, but text instead: [ScoreTextGraphic] Text = ScoreText Now to define the ScoreText which is the section that contains the text information: [ScoreText] String = 10000 The String property contains the actual text characters. This will be the default text when a ScoreObject instance is created in code. Let's now create an instance of the ScoreObject in the Init() function: orxObject_CreateFromConfig("ScoreObject"); So far, the Init() function should look like this: orxSTATUS orxFASTCALL Init() { orxVIEWPORT *viewport = orxViewport_CreateFromConfig("Viewport"); camera = orxViewport_GetCamera(viewport); orxObject_CreateFromConfig("BackgroundObject"); ufo = orxObject_CreateFromConfig("UfoObject"); orxCamera_SetParent(camera, ufo); orxObject_CreateFromConfig("PickupObjects"); orxObject_CreateFromConfig("ScoreObject"); orxClock_Register(orxClock_FindFirst(orx2F(-1.0f), orxCLOCK_TYPE_CORE), Update, orxNULL, orxMODULE_ID_MAIN, orxCLOCK_PRIORITY_NORMAL); orxEvent_AddHandler(orxEVENT_TYPE_PHYSICS, PhysicsEventHandler); return orxSTATUS_SUCCESS; } Compile and run. There should be a score object in the top left hand corner displaying: 10000 The score is pretty small. And it's fixed into the top left corner of the playfield. That's not really what we want. A score is an example of a User Interface (UI) element. It should be fixed in the same place on the screen. Not move around when the screen scrolls. The score should in fact, be fixed as a child to the Camera. Wherever the Camera goes, the score object should go with it. This can be achieved with the ParentCamera property, and then setting the position of the score relative to the camera's centre position: [ScoreObject] Graphic = ScoreTextGraphic Position = (-380, -280, 0) ParentCamera = Camera UseParentSpace = false With these changes, we've stated that we want the Camera to be the parent of the ScoreObject. In other words, we want the ScoreObject to travel with the Camera and appear to be fixed on the screen. By saying that we don't want to UseParentSpace means that we want specify relative world coordinates from the centre of the camera. If we said yes, we'd have to specify coordinates in another system. And Position, of course, is the position relative to the center of the camera. In our case, moved to the top left corner position. Re-run and you'll see the score in much the same position as before, but when you move the ufo around, and the screen scrolls, the score object remains fixed in the same place. The only thing, it's still a little small. We can double its size using Scale: [ScoreObject] Graphic = ScoreTextGraphic Position = (-380, -280, 0) ParentCamera = Camera UseParentSpace = false Scale = 2.0 Smoothing = false Smoothing has been set to false so that when the text is scaled up, it will be sharp and pixellated rather than smoothed up which looks odd. All objects in our project are smooth be default due to: [Display] Smoothing = true: So we need to explicitly set the score to not smooth. Re-run. That looks a lot better. To actually make use of the score object, we will need a variable in code of type int to keep track of the score. Every clock cycle, we'll take that value and change the text on the ScoreObject. That is another cool feature of Orx text objects: the text can be changed any time, and the object will re-render. Finally, when the ufo collides with the pickup, and the pickup is destroyed, the score variable will be increased. The clock will pick up the variable value and set the score object. Begin by creating a score variable at the very top of the code: #include "orx.h" orxOBJECT *ufo; orxCAMERA *camera; int score = 0; Change the comparison code inside the PhysicsEventHandler function to increase the score by 150 points every time a pickup is collected: if (orxString_SearchString(recipientName, "PickupObject") != orxNULL) { orxObject_SetLifeTime(pstRecipientObject, 0); orxObject_AddSound(pstSenderObject, "PickupSound"); score += 150; } if (orxString_SearchString(senderName, "PickupObject") != orxNULL) { orxObject_SetLifeTime(pstSenderObject, 0); orxObject_AddSound(pstRecipientObject, "PickupSound"); score += 150; } Now we need a way to change the text of the score object. We declared the score object in the Init() function as: orxObject_CreateFromConfig("ScoreObject"); But we really need to create it using an orxOBJECT variable: scoreObject = orxObject_CreateFromConfig("ScoreObject"); And then declare the scoreObject at the top of the file: #include "orx.h" orxOBJECT *ufo; orxCAMERA *camera; orxOBJECT *scoreObject; int score = 0; Now it is possible to update the scoreObject using our score variable. At the bottom of the Update() function, add the following code: if (scoreObject) { orxCHAR formattedScore[5]; orxString_Print(formattedScore, "%d", score); orxObject_SetTextString(scoreObject, formattedScore); } First, the block will only execute if there is a valid scoreObject. If so, then create a 5 character string. Then print into the string with the score value, effectively converting an int into a string. Finally set the score text to the scoreObject using the orxObject_SetTextString function. Compile and Run. Move the ufo around and collect the pickups to increase the score 150 points at a time. Winning the game 1200 is the maximum amount of points that can be awarded, and that will mean we've won the game. If we do win, we want a text label to appear above the ufo, saying “You win!”. Like the score object, we need to define a YouWinObject: [YouWinObject] Graphic = YouWinTextGraphic Position = (0, -60, 0.0) Scale = 2.0 Smoothing = false Just like the camera, the YouWinObject is going to be parented to the ufo too. This will give the appearance that the YouWinObject is part of the ufo. The Scale is set to x2. The Position is set offset up in the y axis so that it appears above the ufo. Next, the actual YouWinTextGraphic: [YouWinTextGraphic] Text = YouWinText Pivot = center And the text to render into the YouWinTextGraphic: [YouWinText] String = You Win! We'll test it by creating an instance of the YouWinObject, putting it into a variable, and then parent it to the ufo in the Init() function: orxObject_CreateFromConfig("PickupObjects"); scoreObject = orxObject_CreateFromConfig("ScoreObject"); ufoYouWinTextObject = orxObject_CreateFromConfig("YouWinObject"); orxObject_SetParent(ufoYouWinTextObject, ufo); Then the variable: #include "orx.h" orxOBJECT *ufo; orxCAMERA *camera; orxOBJECT *ufoYouWinTextObject; orxOBJECT *scoreObject; int score = 0; Compile and Run. The “You win” text should appear above the ufo. Not bad, but the text is rotating with the ufo much like the camera was before. We can ignore the rotation from the parent on this object too: [YouWinObject] Graphic = YouWinTextGraphic Position = (0, -60, 0.0) Scale = 2.0 Smoothing = false IgnoreFromParent = rotation Re-run. Interesting. It certainly isn't rotating with the ufo, but its position is still being taken from the ufo's rotation. We need to ignore this as well: [YouWinObject] Graphic = YouWinTextGraphic Position = (0, -60, 0.0) Scale = 2.0 Smoothing = false IgnoreFromParent = position.rotation rotation Good that's working right. We want the “You Win!” to appear once all pickups are collected. The YouWinObject object on created on the screen when the game starts. But we don't want it to appear yet. Only when we win. Therefore, we need to disable the object immediately after it is created using the orxObject_Enable function: ufoYouWinTextObject = orxObject_CreateFromConfig("YouWinObject"); orxObject_SetParent(ufoYouWinTextObject, ufo); orxObject_Enable(ufoYouWinTextObject, orxFALSE); Finally, all that is left to do is add a small check in the PhysicsEventHandler function to test the current score after each pickup collision: if (orxString_SearchString(recipientName, "PickupObject") != orxNULL) { orxObject_SetLifeTime(pstRecipientObject, 0); orxObject_AddSound(pstSenderObject, "PickupSound"); score += 150; } if (orxString_SearchString(senderName, "PickupObject") != orxNULL) { orxObject_SetLifeTime(pstSenderObject, 0); orxObject_AddSound(pstRecipientObject, "PickupSound"); score += 150; } if (orxObject_IsEnabled(ufoYouWinTextObject) == orxFALSE && score == 1200) { orxObject_Enable(ufoYouWinTextObject, orxTRUE); } We are checking two things: that the ufoYouWinTextObject is not yet enabled using the orxObject_IsEnabled function, and if the score is 1200. If both conditions are met, enable the ufoYouWinTextObject. Compile and run. Move the ufo around and collect all the pickups. When all are picked up and 1200 is reached, the “You Win!” text should appear above the ufo signifying that the game is over and we have won. And that brings us to the end! We have created a simple and complete game with some configuration and minimal code. Congratulations! I hope you enjoyed working through making the ufo game using the Orx Portable Game Engine. Of course, there are many little extras you can add to give your game that little extra polish. So, for just a bit more eye candy, there a couple more sections that you can follow along with if you wish. Shadows There are many ways to do shadows. One method is to use shaders… though this method is a little beyond this simple guide. Another method, when making your graphics, would be to add an alpha shadow underneath. This is a good method if your object does not need to rotate or flip. The method I will show you in this chapter is to have a separate shadow object as a child of an object. And in order to remain independent of rotations, the children will ignore rotations from the parent. First a shadow graphic for the ufo, and one for the pickups: Save these both into the data/texture folder. Then create config for the ufo shadow: [UfoShadowGraphic] Texture = ufo-shadow.png Alpha = 0.3 Pivot = center The only interesting part is the Alpha property. 0.1 would be almost completely see-through (or transparent), and 1.0 is not see-through at all, which is the regular default value for a graphic. 0.3 is fairly see-through. [UfoShadowObject] Graphic = UfoShadowGraphic Position = (20, 20, 0.05) Set the Position a bit to the right, and downwards. Next, add the UfoShadowObject as a child of the UfoObject: [UfoObject] Graphic = UfoGraphic Position = (0,0, -0.1) Body = UfoBody AngularVelocity = 200 UseParentSpace = position SoundList = AppearSound ChildList = UfoShadowObject Run the project. The shadow child is sitting properly behind the ufo but it rotates around the ufo, until it ends up at the bottom left which is not correct. We'll need to ignore the rotation from the parent: [UfoShadowObject] Graphic = UfoShadowGraphic Position = (20, 20, 0.05) IgnoreFromParent = position.rotation rotation Not only do we need to ignore the rotation of ufo, we also need to ignore the rotation position of the ufo. Re-run and the shadow sits nice and stable to the bottom right of the ufo. Now to do the same with the pickup shadow: [PickupShadowGraphic] Texture = pickup-shadow.png Alpha = 0.3 Pivot = center [PickupShadowObject] Graphic = PickupShadowGraphic Position = (20, 20, 0.05) IgnoreFromParent = position.rotation The only difference between this object and the ufo shadow, is that we want the pickup shadow to take the rotation value from the parent. But we do not want to take the position rotation. That way, the pickup shadow will remain in the bottom right of the pickup, but will rotate nicely in place. Now attach as a child to the pickup object: [PickupObject] Graphic = PickupGraphic FXList = RotateFX Body = PickupBody ChildList = PickupShadowObject Re-run, and the shadows should all be working correctly. And that really is it this time. I hope you made it this far and that you enjoyed this series of articles on the Orx Portable Game Engine. If you like what you see and would like to try out a few more things with Orx, head over our learning wiki where you can follow more beginner guides, tutorials and examples. You can always get the latest news on Orx at the official website. If you need any help, you can get in touch with the community on gitter, or at the forum. They're a friendly helpful bunch over there, always ready to welcome newcomers and assist with any questions. 0 comments 13. Creating Pickup Objects This is part 4 of a series on creating a game with the Orx Portable Game Engine. Part 1 is here, and part 3 is here. In our game, the player will be required to collect objects scattered around the playfield with the ufo. When the ufo collides with one, the object will disappear, giving the impression that it has been picked up. Begin by creating a config section for the graphic, and then the pickup object: [PickupGraphic] Texture = pickup.png Pivot = center [PickupObject] Graphic = PickupGraphic The graphic will use the image pickup.png which is located in the project's data/object folder. It will also be pivoted in the center which will be handy for a rotation effect later. Finally, the pickup object uses the pickup graphic. Nice and easy. Our game will have eight pickup objects. We need a simple way to have eight of these objects in various places. We will employ a nice trick to handle this. We will make an empty object, called PickupObjects which will hold eight copies of the pickup object as child objects. That way, wherever the parent is moved, the children move with it. Add that now: [PickupObjects] ChildList = PickupObject1 # PickupObject2 # PickupObject3 # PickupObject4 # PickupObject5 # PickupObject6 # PickupObject7 # PickupObject8 Position = (-400, -300, -0.1) This object will have no graphic. That's ok. It can still act like any other object. Notice the position. It is being positioned in the top left hand corner of the screen. All of the child objects PickupObject1 to PickupObject8 will be positioned relative to the parent in the top left corner. Now to create the actual children. We'll use the inheritance trick again, and just use PickupObject as a template: [PickupObject1@PickupObject] Position = (370, 70, -0.1) [PickupObject2@PickupObject] Position = (210, 140, -0.1) [PickupObject3@PickupObject] Position = (115, 295, -0.1) [PickupObject4@PickupObject] Position = (215, 445, -0.1) [PickupObject5@PickupObject] Position = (400, 510, -0.1) [PickupObject6@PickupObject] Position = (550, 420, -0.1) [PickupObject7@PickupObject] Position = (660, 290, -0.1) [PickupObject8@PickupObject] Position = (550, 150, -0.1) Each of the PickupObject* objects uses the properties defined in PickupObject. And the only difference between them are their Position properties. The last thing to do is to create an instance of PickupObjects in code in the Init() function: orxObject_CreateFromConfig("PickupObjects"); Compile and Run. Eight pickup objects should appear on screen. Looking good. It would look good if the pickups rotated slowly on screen, just to make them more interesting. This is very easy to achieve in Orx using FX. FX can also be defined in config. FX allows you to affect an object's position, colour, rotation, scaling, etc, even sound can be affected by FX. Change the PickupObject by adding a FXList property: [PickupObject] Graphic = PickupGraphic FXList = SlowRotateFX Clearly being an FXList you can have many types of FX placed on an object at the same time. We will only have one. An FX is a collection of FX Slots. FX Slots are the actual effects themselves. Confused? Let's work through it. First, the FX: [SlowRotateFX] SlotList = SlowRotateFXSlot Loop = true This simply means, use some effect called SlowRotateFXSlot, and when it is done, do it again in a loop. Next the slot (or effect): [SlowRotateFXSlot] Type = rotation StartTime = 0 EndTime = 10 Curve = linear StartValue = 0 EndValue = 360 That's a few properties. First, the Type, which is a rotation FX. The total time for the FX is 10 seconds, which comes from the StartTime and EndTime properties. The Curve type is linear so that the values changes are done so in a strict and even manner. And the values which the curve uses over the 10 second period starts from 0 and climbs to 360. Re-run and notice the pickups now turning slowly for 10 seconds and then repeating. Picking up the collectable objects Time to make the ufo collide with the pickups. In order for this to work (just like for the walls) the pickups need a body. And the body needs to be set to collide with a ufo and vice versa. First a body for the pickup template: [PickupObject] Graphic = PickupGraphic FXList = SlowRotateFX Body = PickupBody Then the body section itself: [PickupBody] Dynamic = false PartList = PickupPart Just like the wall, the pickups are not dynamic. We don't want them bouncing and traveling around as a result of being hit by the ufo. They are static and need to stay in place if they are hit. Next to define the PickupPart: [PickupPart] Type = sphere Solid = false SelfFlags = pickup CheckMask = ufo The pickup is sort of roundish, so we're going with a spherical type. It is not solid. We want the ufo to able to pass through it when it collides. It should not influence the ufo's travel at all. The pickup is given a label of pickup and will only collide with an object with a label of ufo. The ufo must reciprocate this arrangement (just like a good date) by adding pickup to its list of bodypart check masks: [UfoBodyPart] Type = sphere Solid = true SelfFlags = ufo Friction = 1.2 CheckMask = wall # pickup This is a static bodypart, and we have specified collision actions to occur if the ufo collides with a pickup. But it's a little difficult to test this right now. However you can turn on the debug again to check the body parts: [Physics] Gravity = (0, 0, 0) ShowDebug = true Re-run to see the body parts. Switch off again: [Physics] Gravity = (0, 0, 0) ShowDebug = false To cause a code event to occur when the ufo hits a pickup, we need something new: a physics hander. The hander will run a function of our choosing whenever two objects collide. We can test for these two objects to see if they are the ones we are interested in, and run some code if they are. First, add the physics hander to the end of the Init() function: orxClock_Register(orxClock_FindFirst(orx2F(-1.0f), orxCLOCK_TYPE_CORE), Update, orxNULL, orxMODULE_ID_MAIN, orxCLOCK_PRIORITY_NORMAL); orxEvent_AddHandler(orxEVENT_TYPE_PHYSICS, PhysicsEventHandler); This will create a physics handler, and should any physics event occur, (like two objects colliding) then a function called PhysicsEventHandler will be executed. Our new function will start as: orxSTATUS orxFASTCALL PhysicsEventHandler(const orxEVENT *_pstEvent) { if (_pstEvent->eID == orxPHYSICS_EVENT_CONTACT_ADD) { orxOBJECT *pstRecipientObject, *pstSenderObject; /* Gets colliding objects */ pstRecipientObject = orxOBJECT(_pstEvent->hRecipient); pstSenderObject = orxOBJECT(_pstEvent->hSender); const orxSTRING recipientName = orxObject_GetName(pstRecipientObject); const orxSTRING senderName = orxObject_GetName(pstSenderObject); orxLOG("Object %s has collided with %s", senderName, recipientName); return orxSTATUS_SUCCESS; } } Every handler function passes an orxEVENT object in. This structure contains a lot of information about the event. The eID is tested to ensure that the type of physics event that has occurred is a orxPHYSICS_EVENT_CONTACT_ADD which indicates when objects collide. If true, then two orxOBJECT variables are declared, then set from the orxEVENT structure. They are passed in as the hSender and hRecipient objects. Next, two orxSTRINGs are declared and are set by getting the names of the objects using the orxObject_GetName function. The name that is returned is the section name from the config. Potential candidates are: UfoObject, BackgroundObject, and PickupObject1 to PickupObject8. The names are then sent to the console. Finally, the function returns orxSTATUS_SUCCESS which is required by an event function. Compile and run. If you drive the ufo into a pickup or the edge of the playfield, a message will display on the console. So we know that all is working. Next is to add code to remove a pickup from the playfield if the ufo collides with it. Usually we could compare the name of one object to another and perform the action. In this case, however, the pickups are named different things: PickupObject1, PickupObject2, PickupObject3… up to PickupObject8. So we will need to actually just check if the name contains “PickupObject” which will match well for any of them. In fact, we don't need to test for the “other” object in the pair of colliding objects. Ufo is a dynamic object and everything else on screen is static. So if anything collides with PickupObject*, it has to be the ufo. Therefore, we won't need to test for that. First, remove the orxLOG line. We don't need that anymore. Change the function to become: orxSTATUS orxFASTCALL PhysicsEventHandler(const orxEVENT *_pstEvent) { if (_pstEvent->eID == orxPHYSICS_EVENT_CONTACT_ADD) { orxOBJECT *pstRecipientObject, *pstSenderObject; /* Gets colliding objects */ pstRecipientObject = orxOBJECT(_pstEvent->hRecipient); pstSenderObject = orxOBJECT(_pstEvent->hSender); const orxSTRING recipientName = orxObject_GetName(pstRecipientObject); const orxSTRING senderName = orxObject_GetName(pstSenderObject); if (orxString_SearchString(recipientName, "PickupObject") != orxNULL) { orxObject_SetLifeTime(pstRecipientObject, 0); } if (orxString_SearchString(senderName, "PickupObject") != orxNULL) { orxObject_SetLifeTime(pstSenderObject, 0); } } return orxSTATUS_SUCCESS; } You can see the new code additions after the object names. If an object name contains the word “PickupObject”, then the ufo must have collided with it. Therefore, we need to kill it off. The safest way to do this is by setting the object's lifetime to 0. This will ensure the object is removed instantly and deleted by Orx in a safe manner. Notice that the test is performed twice. Once, if the pickup object is the sender, and again if the object is the recipient. Therefore we need to check and handle both. Compile and run. Move the ufo over the pickups and they should disappear nicely. We'll leave it there for the moment. In the final, Part 5, we'll cover adding sounds, a score, and winning the game. 0 comments 14. Collisions This is part 3 of a series on creating a game with the Orx Portable Game Engine. Part 1 is here, and Part 2 is here. There is one last requirement for the collision to occur: we need to tell the physics system, who can collide with who. This is done with flags and masks. Make a change to the ufo's body part by adding SelfFlags and CheckMask: [UfoBodyPart] Type = sphere Solid = true SelfFlags = ufo CheckMask = wall SelfFlags is the label you assign to one object, and CheckMask is the list of labels that your object can collide with. These labels don't have to match the names you give objects, however it will help you stay clean and organised. So in the config above, we are saying: the UfoBodyPart is a “ufo” and it is expected to collide with any bodypart marked as a “wall”. But we haven't done that yet, so let's do it now. We will only need to add it to the WallTopPart: [WallTopPart] Type = box Solid = true SelfFlags = wall CheckMask = ufo TopLeft = (-400, -300, 0) BottomRight = (400, -260, 0) Remember, that the other three wall parts inherit the values from WallTopPart. So each now carries the label of “wall” and they will collide with any other body part that carries the label of “ufo”. Re-run and press the left arrow key and drive the ufo into the left wall. It collides! And it stops. Now that the collision is working, we can flesh out the rest of the keyboard controls and test all four walls: void orxFASTCALL Update(const orxCLOCK_INFO *_pstClockInfo, void *_pContext) { if (ufo) { const orxFLOAT FORCE = 0.8; orxVECTOR rightForce = { FORCE, 0, 0 }; orxVECTOR leftForce = { -FORCE, 0, 0 }; orxVECTOR upForce = { 0, -FORCE, 0 }; orxVECTOR downForce = { 0, FORCE, 0 }; if (orxInput_IsActive("GoLeft")) { orxObject_ApplyForce(ufo, &leftForce, orxNULL); } if (orxInput_IsActive("GoRight")) { orxObject_ApplyForce(ufo, &rightForce, orxNULL); } if (orxInput_IsActive("GoUp")) { orxObject_ApplyForce(ufo, &upForce, orxNULL); } if (orxInput_IsActive("GoDown")) { orxObject_ApplyForce(ufo, &downForce, orxNULL); } } } Now is a good time to turn off the physics debug as we did earlier on. Compile and run. Try all four keys, and you should be able to move the ufo around the screen. The ufo can also collide with each wall. The ufo is a little boring in the way that it doesn't spin when colliding with a wall. We need to ensure the UfoBody is not using fixed rotation. While this value defaults to false when not supplied, it will make things more readable if we explicitly set it: [UfoBody] Dynamic = true PartList = UfoBodyPart FixedRotation = false The active ingredient here is to ensure that both the wall bodypart and the ufo bodypart both have a little friction applied. This way when they collide, they will drag against each other and produce some spin: [UfoBodyPart] Type = sphere Solid = true SelfFlags = ufo CheckMask = wall Friction = 1.2 [WallTopPart] Type = box Solid = true SelfFlags = wall CheckMask = ufo TopLeft = (-400, -300, 0) BottomRight = (400, -260, 0) Friction = 1.2 Re-run that and give it a try. Run against a wall on angle to get some spin on the ufo. The next thing to notice is that both the movement of the ufo and the spin never slow down. There is no friction to slow those down. We'll deal with the spin first. By adding some AngularDamping on the UfoBody, the spin will slow down over time: [UfoBody] Dynamic = true PartList = UfoBodyPart AngularDamping = 2 FixedRotation = false Re-run and check the spin. The ufo should be slowing down after leaving the wall. Now for the damping on the movement. That can be done with LinearDamping on the UfoBody: [UfoBody] Dynamic = true PartList = UfoBodyPart AngularDamping = 2 FixedRotation = false LinearDamping = 5 Re-run and the speed will slow down after releasing the arrow keys. But it's slower overall as well. Not 100% what we want. You can increase the FORCE value in code (ufo.cpp), in the Update function to compensate: const orxFLOAT FORCE = 1.8; Compile and run. The speed should be more what we expect. It would be nice for the ufo to be already spinning a little when the game starts. For this, add a little AngularVelocity : [UfoObject] Graphic = UfoGraphic Position = (0, 0, -0.1) Body = UfoBody AngularVelocity = 200 Run this and the ship will have a small amount of spin at the start until the AngularDamping on the ufo body slows it down again. Following the UFO with the camera While we can simply move the ufo around with the keys on a fixed background, it will be a more pleasant experience to have the ufo fixed and have the screen scroll around instead. This effect can be achieved by parenting the camera to the ufo so that wherever the ufo goes, the camera goes. Currently, our project is set up so that the viewport has a camera configured to it. But the camera is not available to our code. We will require the camera to be available in a variable so that it can be parented to the ufo object. To fix this, in the Init() function, extract the camera from the viewport into a variable by first removing this line: orxViewport_CreateFromConfig("Viewport"); to: orxVIEWPORT *viewport = orxViewport_CreateFromConfig("Viewport"); camera = orxViewport_GetCamera(viewport); And because the camera variable isn't defined, do so at the top of the code: #include "orx.h" orxOBJECT *ufo; orxCAMERA *camera; Now it is time to parent the camera to the ufo in the init() function using the orxCamera_SetParent function: ufo = orxObject_CreateFromConfig("UfoObject"); orxCamera_SetParent(camera, ufo); Compile and Run. Woah, hang on. That's crazy, the whole screen just rotated around when ufo. And it continues to rotate when hitting the ufo against the walls. See how the camera is a child of the ufo now? Not only does the camera move with the ufo, it rotates with it as well. We certainly want it to move with the ufo, but it would be nice ignore the rotation from the parent ufo. Add the IgnoreFromParent property to the MainCamera section: [MainCamera] FrustumWidth = 1024 FrustumHeight = 720 FrustumFar = 2.0 FrustumNear = 0.0 Position = (0.0, 0.0, -1.0) IgnoreFromParent = rotation Re-run. That's got it fixed. Now when you move around, the playfield will appear to scroll rather than it being the ufo that moves. This makes for a more dramatic and interesting effect. In Part 4, we will give the ufo something to do. The goal is to collect several pickups. 0 comments 15. The UFO This is part 2 of a series on creating a game with the Orx Portable Game Engine. Part 1 is here. We have a playfield, and now we need a UFO character for the player to control. The first step is the create the configuration for the ufo object in ufo.ini: [UfoObject] Graphic = UfoGraphic Position = (0, 0, -0.1) This indicates that the UfoObject should use a graphic called UfoGraphic. Secondly, its position will be centered in the playfield with (x,y) = (0,0). The -0.1 is the Z-axis, and this will be placed above the BackgroundObject whose Z-axis is set to 0. Then the UfoGraphic which the UfoObject needs: [UfoGraphic] Texture = ufo.png Pivot = center Unlike the background object, our ufo object will need to be assigned to a variable. This will make it possible to affect the ufo using code: Create the variable for our ufo object just under the orx.h include line: #include "orx.h" orxOBJECT *ufo; And in the Init() function, create an instance of the ufo object with: ufo = orxObject_CreateFromConfig("UfoObject"); Compile and run. You'll see a ufo object in front of the background. Excellent. Time to move to something a little more fun, moving the ufo. Controlling the UFO The ufo is going to be controlled using the cursor arrow keys on the keyboard. The ufo will be moved by applying forces. Physics will be set up in the project in order to do this. Also, we will use a clock to call an update function regularly. This function will read and respond to key presses. Defining Direction Keys Defining the keys is very straight forward. In the config file, expand the MainInput section in the ufo.ini by adding the four cursor keys: [MainInput] KEY_ESCAPE = Quit KEY_UP = GoUp KEY_DOWN = GoDown KEY_LEFT = GoLeft KEY_RIGHT = GoRight Each key is being given a label name, like: GoUp or GoDown. These label names are available in our code to test against. The next step is to create an update callback function in our code where the keys presses are checked: void orxFASTCALL Update(const orxCLOCK_INFO *_pstClockInfo, void *_pContext) { } And in order to tie this function to a clock (the clock will execute this function over and over), add the following to bottom of the Init() function: orxClock_Register(orxClock_FindFirst(orx2F(-1.0f), orxCLOCK_TYPE_CORE), Update, orxNULL, orxMODULE_ID_MAIN, orxCLOCK_PRIORITY_NORMAL); That looks very scary and intimidating, but the only part that is important to you is the parameter with “Update”. This means, tell the existing core clock to continually call our “Update” function. Of course you can specify any function name here you like as long as it exists. Let's test a key to ensure that our event is working well. Add the following code into the Update function: void orxFASTCALL Update(const orxCLOCK_INFO *_pstClockInfo, void *_pContext) { if (ufo) { if (orxInput_IsActive("GoLeft")) { orxLOG("LEFT PRESSED!"); } } } Every time Update is run, ufo is tested to ensure it exists, and then moves to check the input system for the label “GoLeft” (if it is active or pressed). Remember how GoLeft is bound to KEY_LEFT in the MainInput config section? If that condition is true, send “LEFT PRESSED!” to the console output window while the key is pressed or held down. Soon we'll replace the orxLOG line with a function that places force on the ufo. But before that, we need to add physics to the ufo. Compile and run. Press the left arrow key and take note of the console window. Every time you press or hold the key, the message is printed. Good, so key presses are working. Physics In order to affect the ufo using forces, physics need to be enabled. Begin by adding a Physics config section and setting Gravity with: [Physics] Gravity = (0, 980, 0) In order for an object in Orx to be affected by physics, it needs both a dynamic body, and at least one bodypart. Give the ufo a body with the Body property: [UfoObject] Graphic = UfoGraphic Position = (0, 0, -0.1) Body = UfoBody Next, create the UfoBody section and define the UfoBodyPart property: [UfoBody] Dynamic = true PartList = UfoBodyPart The body part is set to Dynamic which means that it is affected by gravity and collisions. A body needs at least one part, and so we need to define the UfoBodyPart: [UfoBodyPart] Type = sphere Solid = true The body part Type is set to be a sphere which will automatically size itself around the object's size, and the body is to be solid so that if it should collide with anything, it will not pass through it. Compile and Run. The ufo falls through the floor. This is because of the gravity setting of 980 in the y axis which simulates world gravity. Our game is a top down game. So change the Gravity property to: [Physics] Gravity = (0, 0, 0) Re-run (no compile needed) and the ufo should remain in the centre of the screen. The Physics section has another handy property available to visually test physics bodies on objects: ShowDebug. Add this property with true: [Physics] Gravity = (0, 0, 0) ShowDebug = true Re-run, and you will see a pinkish sphere outline automatically sized around the ufo object. For now we'll turn that off again. You can do this by changing the ShowDebug value to false, adding a ; comment in front of the line or simply just deleting the line. We'll set our ShowDebug to false: [Physics] Gravity = (0, 0, 0) ShowDebug = false Let's add some force to the ufo if the left cursor key is pressed. Change the code in the Update function to be: void orxFASTCALL Update(const orxCLOCK_INFO *_pstClockInfo, void *_pContext) { if (ufo) { const orxFLOAT FORCE = 0.8; orxVECTOR leftForce= { -FORCE, 0, 0 }; if (orxInput_IsActive("GoLeft")) { orxObject_ApplyForce(ufo, &leftForce, orxNULL); } } } The orxObject_ApplyForce function takes an orxVECTOR facing left and applies it to the ufo object. Compile and re-run. If you press and release the left arrow key, the ufo will move to the left. If you hold the left key down, the ufo will increase its speed and move out the left hand side of the screen. Even if you tap the left key once quickly, the ufo will still eventually travel out of the left of the screen. There is no friction yet to slow it down, or any barriers to stop it going out of the screen. Barrier Around The Border Even though the background looks it has a border, it is really only a picture. In order to create a barrier for the ufo, we will need to wrap the edges using some body parts. This means, the background object will also be given a body, and four body parts, one for each wall. Start with adding a body to the object: [BackgroundObject] Graphic = BackgroundGraphic Position = (0, 0, 0) Body = WallBody And then the body itself: [WallBody] Dynamic = false PartList = WallTopPart # WallRightPart # WallBottomPart # WallLeftPart This is different from the ufo body. This body is not dynamic. This means that it is a static body, one that cannot be affected by gravity. But dynamic objects can still collide with it. Also, there are four parts to this body, unlike the ufo which only had one. Start with the WallTopPart first: [WallTopPart] Type = box Solid = true TopLeft = (-400, -300, 0) BottomRight = (400, -260, 0) In this part, the type is a box body part. It is set to solid for collisions, ie so that a dynamic object can collide with it but not pass though it. Stretch the box to cover the region from (-400,-300) to (400, -260). At this point, it might be a good idea to turn on the physics debugging to check our work: [Physics] Gravity = (0, 0, 0) ShowDebug = true Re-run the project. The top wall region should cover the top barrier squares: Great. Next, we'll do the right hand side. But rather than copy all the same values, we'll reuse some from the top wall: [WallRightPart@WallTopPart] TopLeft = (360, -260,0) BottomRight = (400, 260, 0) Notice the @WallTopPart in the section name? This means: copy all the values from WallTopPart, but any properties in WallRightPart will take priority. Therefore, use the Type, and Solid properties from WallTopPart, but use our own values for TopLeft and BottomRight for the WallRightPart section. This is called “Section Inheritance”. This will come in very handy soon when we tweak values or add new properties to all four wall parts. Re-run the project, and there will now be two walls. Define the last two walls using the same technique: [WallBottomPart@WallTopPart] TopLeft = (-400,260,0) BottomRight = (400, 300, 0) [WallLeftPart@WallTopPart] TopLeft = (-400,-260,0) BottomRight = (-360, 260, 0) Now there are four walls for the ufo to collide with. Re-run and try moving the ufo left into the wall. Oops, it doesn't work. It still passes straight though. There is one last requirement for the collision to occur: we need to tell the physics system, who can collide with who. We'll cover that in Part 3. 0 comments 16. Overview Welcome to the 2D UFO game guide using the Orx Portable Game Engine. My aim for this tutorial is to take you through all the steps to build a UFO game from scratch. The aim of our game is to allow the player to control a UFO by applying physical forces to move it around. The player must collect pickups to increase their score to win. I should openly acknowledge that this series is cheekily inspired by the 2D UFO tutorial written for Unity. It makes an excellent comparison of the approaches between Orx and Unity. It is also a perfect way to highlight one of the major parts that makes Orx unique among other game engines, its Data Driven Configuration System. You'll get very familiar with this system very soon. It's at the very heart of just about every game written using Orx. If you are very new to game development, don't worry. We'll take it nice and slow and try to explain everything in very simple terms. The only knowledge you will need is some simple C++. I'd like say a huge thank you to FullyBugged for providing the graphics for this series of articles. What are we making? Visit the video below to see the look and gameplay of the final game: Getting Orx The latest up to date version of Orx can be cloned from github and set up with: git clone https://github.com/orx/orx.git Once cloning has completed, the setup script in the root of the files will start automatically for you. This script creates an$ORX environment variable for your system. The variable will point to the code subfolder where you cloned Orx. Why? I'll get to the in a moment, but it'll make your life easier. The setup script also creates several projects for various IDEs and operating system: Visual Studio, Codelite, Code::Blocks, and gmake. You can pick one of these projects to build the Orx library. Building the Orx Library While the Orx headers are provided, you need to compile the Orx library so that your own games can link to it. Because the setup script has already created a suitable a project for you (using premake), you can simply open one for your chosen OS/IDE and compile the Orx library yourself. There are three configurations to compile: Debug, Profile and Release. You will need to compile all three. For more details on compiling the Orx lbrary at: http://orx-project.org/wiki/en/tutorials/cloning_orx_from_github at the Orx learning wiki. The $ORX Environment Variable I promised I would explain what this is for. Once you have compiled all three orx library files, you will find them in the code/lib/dynamic folder: orx.dll orxd.dll orxp.dll Also, link libraries will be available in the same folder: orx.lib orxd.lib orxp.lib When it comes time to create our own game project, we would normally be forced to copy these library files and includes into every project. A better way is to have our projects point to the libraries and includes located at the folder that the$ORX environment variable points to (for example: C:\Dev\orx\code). This means that your projects will always know where to find the Orx library. And should you ever clone and re-compile a new version of Orx, your game projects can make immediate use of the newer version. Setting up a 2D UFO Project Now the you have the Orx libraries cloned and compiled, you will need a blank project for your game. Supported options are: Visual Studio, CodeLite, Code::Blocks, XCode or gmake, depending on your operating system. Once you have a game project, you can use it to work through the steps in this tutorial. Orx provides a very nice system for auto creating game projects for you. In the root of the Orx repo, you will find either the init.bat (for Windows) or init.sh (Mac/Linux) command. Create a project for our 2D game from the command line in the Orx folder and running: init c:\temp\ufo or init.sh ~/ufo Orx will create a project for each IDE supported by your OS at the specified location. You can copy this folder anywhere, and your project will always compile and link due to the $ORX environment variable. It knows where the libraries and includes are for Orx. Open your project using your favourite IDE from within the ufo/build folder. When the blank template loads, there are two main folders to note in your solution: config src Firstly, the src folder contains a single source file, ufo.cpp. This is where we will add the c++ code for the game. The config folder contains configuration files for our game. What is config? Orx is a data driven 2D game engine. Many of the elements in your game, like objects, spawners, music etc, do not need to be defined in code. They can be defined (or configured) using config files. You can make a range of complex multi-part objects with special behaviours and effects in Orx, and bring them into your game with a single line of code. You'll see this in the following chapters of this guide. There are three ufo config files in the config folder but for this guide, only one will actually be used in our game. This is: ufo.ini All our game configuration will be done there. Over in the Orx library repo folder under orx/code/bin, there are two other config files: CreationTemplate.ini SettingsTemplate.ini These are example configs and they list all the properties and values that are available to you. We will mainly concentrate on referring to the CreationTemplate.ini, which is for objects, sounds, etc. It's good idea to include these two files into your project for easy reference. Alternatively you can view these online at https://github.com/orx/orx/blob/master/code/bin/CreationTemplate.ini and here: https://github.com/orx/orx/blob/master/code/bin/SettingsTemplate.ini The code template Now to take a look at the basic ufo.cpp and see what is contained there. The first function is the Init() function. This function will execute when the game starts up. Here you can create objects have been defined in the config, or perform other set up tasks like handlers. We'll do both of these soon. The Run() function is executed every main clock cycle. This is a good place to continually perform a task. Though there are better alternatives for this, and we will cover those later. This is mainly used to check for the quit key. The Exit() function is where memory is cleaned up when your game quits. Orx cleans up nicely after itself. We won't use this function as part of this guide. The Bootstrap() function is an optional function to use. This is used to tell Orx where to find the first config file for use in our game (ufo.ini). There is another way to do this, but for now, we'll use this function to inform Orx of the config. Then of course, the main() function. We do not need to use this function in this guide. Now that we have everything we need to get start, you should be able to compile successfully. Run the program and an Orx logo will appear slowly rotating. Great. So now you have everything you need to start building the UFO game. If you experience an issue compiling, check the troubleshooting article for Orx projects for help. Setting up the game assets Our game will have a background, a UFO which the player will control, and some pickups that the player can collect. The UFO will be controlled by the player using the cursor keys. First you'll need the assets to make the game. You can download the file assets-for-orx-ufo-game.zip which contains: The background file (background.png😞 The UFO and Pickup sprite images (ufo.png and pickup.png😞 And a pickup sound effect (pickup.ogg😞 pickup.ogg Copy the .png files into your data/texture folder Copy the .ogg file into your data/sound folder. Now these files can be accessed by your project and included in the game. Setting up the Playfield We will start by setting up the background object. This is done using config. Open the ufo.ini config file in your editor and add the following: [BackgroundGraphic] Texture = background.png Pivot = center The BackgroundGraphic defined here is called a Graphic Section. It has two properties defined. The first is Texture which has been set as background.png. The Orx library knows where to find this image, due to the properties set in the Resource section: [Resource] Texture = ../../data/texture So any texture files that are required (just like in our BackgroundGraphic section) will be located in the ../../data/texture folder. The second parameter is Pivot. A pivot is the handle (or sometimes “hotspot” in other frameworks). This is set to be center. The position is 0,0 by default, just like the camera. The effect is to ensure the background sits in the center of our game window. There are other values available for Pivot. To see the list of values, open the CreationTemplate.ini file in your editor. Scroll to the GraphicTemplate section and find Pivot in the list. There you can see all the possible values that could be used. top left is also a typical value. We need to define an object that will make use of this graphic. This will be the actual entity that is used in the game: [BackgroundObject] Graphic = BackgroundGraphic Position = (0, 0, 0) The Graphic property is the section BackgroundGraphic that we defined earlier. Our object will use that graphic. The second property is the Position. In our world, this object will be created at (0, 0, 0). In Orx, the coordinates are (x, y, z). It may seem strange that Orx, being a 2D game engine has a Z axis. Actually Orx is 2.5D. It respects the Z axis for objects, and can use this for layering above or below other objects in the game. To make the object appear in our game, we will add a line of code in our source file to create it. In the Init() function of ufo.cpp, remove the default line: orxObject_CreateFromConfig("Object"); and replace it with: orxObject_CreateFromConfig("BackgroundObject"); Compile and run. The old spinning logo is now replaced with a nice tiled background object. Next, the ufo object is required. This is what the player will control. This will be covered in Part 2. 4 comments 17. The more you know about a given topic, the more you realize that no one knows anything. For some reason (why God, why?) my topic of choice is game development. Everyone in that field agrees: don't add networked multiplayer to an existing game, you drunken clown. Well, I did it anyway because I hate myself. Somehow it turned out great. None of us know anything. Problem #1: assets My first question was: how do I tell a client to use such-and-such mesh to render an object? Serialize the whole mesh? Nah, they already have it on disk. Send its filename? Nah, that's inefficient and insecure. Okay, just a string identifier then? Fortunately, before I had time to implement any of my own terrible ideas, I watched a talk from Mike Acton where he mentions the danger of "lazy decision-making". One of his points was: strings let you lazily ignore decisions until runtime, when it's too late to fix. If I rename a texture, I don't want to get a bug report from a player with a screenshot like this: I had never thought about how powerful and complex strings are. Half the field of computer science deals with strings and what they can do. They usually require a heap allocation, or something even more complex like ropes and interning. I usually don't bother to limit their length, so a single string expands the possibility space to infinity, destroying whatever limited ability I had to predict runtime behavior. And here I am using these complex beasts to identify objects. Heck, I've even used strings to access object properties. What madness! Long story short, I cultivated a firm conviction to avoid strings where possible. I wrote a pre-processor that outputs header files like this at build time: namespace Asset { namespace Mesh { const int count = 3; const AssetID player = 0; const AssetID enemy = 1; const AssetID projectile = 2; } } So I can reference meshes like this: renderer->mesh = Asset::Mesh::player; If I rename a mesh, the compiler makes it my problem instead of some poor player's problem. That's good! The bad news is, I still have to interact with the file system, which requires the use of strings. The good news is the pre-processor can save the day. const char* Asset::Mesh::filenames[] = { "assets/player.msh", "assets/enemy.msh", "assets/projectile.msh", 0, }; With all this in place, I can easily send assets across the network. They're just numbers! I can even verify them. if (mesh < 0 || mesh >= Asset::Mesh::count) net_error(); // just what are you trying to pull, buddy? Problem #2: object references My next question was: how do I tell a client to please move/delete/frobnicate "that one object from before, you know the one". Once again, I was lucky enough to hear from smart people before I could shoot myself in the foot. From the start, I knew I needed a bunch of lists of different kinds of objects, like this: Array<Turret> Turret::list; Array<Projectile> Projectile::list; Array<Avatar> Avatar::list; Let's say I want to reference the first object in the Avatar list, even without networking, just on our local machine. My first idea is to just use a pointer: Avatar* avatar; avatar = &Avatar::list[0]; This introduces a ton of non-obvious problems. First, I'm compiling for a 64 bit architecture, which means that pointer takes up 8 whole bytes of memory, even though most of it is probably zeroes. And memory is the number one performance bottleneck in games. Second, if I add enough objects to the array, it will get reallocated to a different place in memory, and the pointer will point to garbage. Okay, fine. I'll use an ID instead. template<typename Type> struct Ref { short id; inline Type* ref() { return &Type::list[id]; } // overloaded "=" operator omitted }; Ref<Avatar> avatar = &Avatar::list[0]; avatar.ref()->frobnicate(); Second problem: if I remove that Avatar from the list, some other Avatar will get moved into its place without me knowing. The program will continue, blissfully and silently screwing things up, until some player sends a bug report that the game is "acting weird". I much prefer the program to explode instantly so I at least get a crash dump with a line number. Okay, fine. Instead of actually removing the avatar, I'll put a revision number on it: struct Avatar { short revision; }; template<typename Type> struct Ref { short id; short revision; inline Type* ref() { Type* t = &Type::list[id]; return t->revision == revision ? t : nullptr; } }; Instead of actually deleting the avatar, I'll mark it dead and increment the revision number. Now anything trying to access it will give a null pointer exception. And serializing a reference across the network is just a matter of sending two easily verifiable numbers. Problem #3: delta compression If I had to cut this article down to one line, it would just be a link to Glenn Fiedler's blog. Which by the way is here: gafferongames.com As I set out to implement my own version of Glenn's netcode, I read this article, which details one of the biggest challenges of multiplayer games. Namely, if you just blast the entire world state across the network 60 times a second, you could gobble up 17 mbps of bandwidth. Per client. Delta compression is one of the best ways to cut down bandwidth usage. If a client already knows where an object is, and it hasn't moved, then I don't need to send its position again. This can be tricky to get right. The first part is the trickiest: does the client really know where the object is? Just because I sent the position doesn't mean the client actually received it. The client might send an acknowledgement back that says "hey I received packet #218, but that was 0.5 seconds ago and I haven't gotten anything since." So to send a new packet to that client, I have to remember what the world looked like when I sent out packet #218, and delta compress the new packet against that. Another client might have received everything up to packet #224, so I can delta compress the new packet differently for them. Point is, we need to store a whole bunch of separate copies of the entire world. Someone on Reddit asked "isn't that a huge memory hog"? No, it is not. Actually I store 255 world copies in memory. All in a single giant array. Not only that, but each copy has enough room for the maximum number of objects (2048) even if only 2 objects are active. If you store an object's state as a position and orientation, that's 7 floats. 3 for XYZ coordinates and 4 for a quaternion. Each float takes 4 bytes. My game supports up to 2048 objects. 7 floats * 4 bytes * 2048 objects * 255 copies = ... 14 MB. That's like, half of one texture these days. I can see myself writing this system five years ago in C#. I would start off immediately worried about memory usage, just like that Redditor, without stopping to think about the actual data involved. I would write some unnecessary, crazy fancy, bug-ridden compression system. Taking a second to stop and think about actual data like this is called Data-Oriented Design. When I talk to people about DOD, many immediately say, "Woah, that's really low-level. I guess you want to wring out every last bit of performance. I don't have time for that. Anyway, my code runs fine." Let's break down the assumptions in this statement. Assumption 1: "That's really low-level". Look, I multiplied four numbers together. It's not rocket science. Assumption 2: "You sacrifice readability and simplicity for performance." Let's picture two different solutions to this netcode problem. For clarity, let's pretend we only need 3 world copies, each containing up to 2 objects. Here's the solution I just described. Everything is statically allocated in the .bss segment. It never moves around. Everything is the same size. No pointers at all. Here's the idiomatic C# solution. Everything is scattered randomly throughout the heap. Things can get reallocated or moved right in the middle of a frame. The array is jagged. 64-bit pointers all over the place. Which is simpler? The second diagram is actually far from exhaustive. C#-land is a lot more complex in reality. Check the comments and you'll probably find someone correcting me about how C# actually works. But that's my point. With my solution, I can easily construct a "good enough" mental model to understand what's actually happening on the machine. I've barely scratched the surface with the C# solution. I have no idea how it will behave at runtime. Assumption 3: "Performance is the only reason you would code like this." To me, performance is a nice side benefit of data-oriented design. The main benefit is clarity of thought. Five years ago, when I sat down to solve a problem, my first thought was not about the problem itself, but how to shoehorn it into classes and interfaces. I witnessed this analysis paralysis first-hand at a game jam recently. My friend got stuck designing a grid for a 2048-like game. He couldn't figure out if each number was an object, or if each grid cell was an object, or both. I said, "the grid is an array of numbers. Each operation is a function that mutates the grid." Suddenly everything became crystal clear to him. Assumption 4: "My code runs fine". Again, performance is not the main concern, but it's important. The whole world switched from Firefox to Chrome because of it. Try this experiment: open up calc.exe. Now copy a 100 MB file from one folder to another. I don't know what calc.exe is doing during that 300ms eternity, but you can draw your own conclusions from my two minutes of research: calc.exe actually launches a process called Calculator.exe, and one of the command line arguments is called "-ServerName". Does calc.exe "run fine"? Did throwing a server in simplify things at all, or is it just slower and more complex? I don't want to get side-tracked. The point is, I want to think about the actual problem and the data involved, not about classes and interfaces. Most of the arguments against this mindset amount to "it's different than what I know". Problem #4: lag I now hand-wave us through to the part of the story where the netcode is somewhat operational. Right off the bat I ran into problems dealing with network lag. Games need to respond to players immediately, even if it takes 150ms to get a packet from the server. Projectiles were particularly useless under laggy network conditions. They were impossible to aim. I decided to re-use those 14 MB of world copies. When the server receives a command to fire a projectile, it steps the world back 150ms to the way the world appeared to the player when they hit the fire button. Then it simulates the projectile and steps the world forward until it's up to date with the present. That's where it creates the projectile. I ended up having the client create a fake projectile immediately, then as soon as it hears back from the server that the projectile was created, it deletes the fake and replaces it with the real thing. If all goes well, they should be in the same place due to the server's timey-wimey magic. Here it is in action. The fake projectile appears immediately but goes right through the wall. The server receives the message and fast-forwards the projectile straight to the part where it hits the wall. 150ms later the client gets the packet and sees the impact particle effect. The problem with netcode is, each mechanic requires a different approach to lag compensation. For example, my game has an "active armor" ability. If players react quick enough, they can reflect damage back at enemies. This breaks down in high lag scenarios. By the time the player sees the projectile hitting their character, the server has already registered the hit 100ms ago. The packet just hasn't made it to the client yet. This means you have to anticipate incoming damage and react long before it hits. Notice in the gif above how early I had to hit the button. To correct this, the server implements something I call "damage buffering". Instead of applying damage instantly, the server puts the damage into a buffer for 100ms, or whatever the round-trip time is to the client. At the end of that time, it either applies the damage, or if the player reacted, reflects it back. Here it is in action. You can see the 200ms delay between the projectile hitting me and the damage actually being applied. Here's another example. In my game, players can launch themselves at enemies. Enemies die instantly to perfect shots, but they deflect glancing blows and send you flying like this: Which direction should the player bounce? The client has to simulate the bounce before the server knows about it. The server and client need to agree which direction to bounce or they'll get out of sync, and they have no time to communicate beforehand. At first I tried quantizing the collision vector so that there were only six possible directions. This made it more likely that the client and server would choose the same direction, but it didn't guarantee anything. Finally I implemented another buffer system. Both client and server, when they detect a hit, enter a "buffer" state where the player sits and waits for the remote host to confirm the hit. To minimize jankiness, the server always defers to the client as to which direction to bounce. If the client never acknowledges the hit, the server acts like nothing happened and continues the player on their original course, fast-forwarding them to make up for the time they sat still waiting for confirmation. Problem #5: jitter My server sends out packets 60 times per second. What about players whose computers run faster than that? They'll see jittery animation. Interpolation is the industry-standard solution. Instead of immediately applying position data received from the server, you buffer it a little bit, then you blend smoothly between whatever data that you have. In my previous attempt at networked multiplayer, I tried to have each object keep track of its position data and smooth itself out. I ended up getting confused and it never worked well. This time, since I could already easily store the entire world state in a struct, I was able to write just two functions to make it work. One function takes two world states and blends them together. Another function takes a world state and applies it to the game. How big should the buffer delay be? I originally used a constant until I watched a video from the Overwatch devs where they mention adaptive interpolation delay. The buffer delay should smooth out not only the framerate from the server, but also any variance in packet delivery time. This was an easy win. Clients start out with a short interpolation delay, and any time they're missing a packet to interpolate toward, they increase their "lag score". Once it crosses a certain threshold, they tell the server to switch them to a higher interpolation delay. Of course, automated systems like this often act against the user's wishes, so it's important to add switches and knobs to the algorithm! Problem #6: joining servers mid-match Wait, I already have a way to serialize the entire game state. What's the hold up? Turns out, it takes more than one packet to serialize a fresh game state from scratch. And each packet may take multiple attempts to make it to the client. It may take a few hundred milliseconds to get the full state, and as we've seen already, that's an eternity. If the game is already in progress, that's enough time to send 20 packets' worth of new messages, which the client is not ready to process because it hasn't loaded yet. The solution is—you guessed it—another buffer. I changed the messaging system to support two separate streams of messages in the same packet. The first stream contains the map data, which is processed as soon as it comes in. The second stream is just the usual fire-hose of game messages that come in while the client is loading. The client buffers these messages until it's done loading, then processes them all until it's caught up. Problem #7: cross-cutting concerns This next part may be the most controversial. Remember that bit of gamedev wisdom from the beginning? "don't add networked multiplayer to an existing game"? Well, most of the netcode in this game is literally tacked on. It lives in its own 5000-line source file. It reaches into the game, pokes stuff into memory, and the game renders it. Just listen a second before stoning me. Is it better to group all network code in one place, or spread it out inside each game object? I think both approaches have advantages and disadvantages. In fact, I use both approaches in different parts of the game, for various reasons human and technical. But some design paradigms (*cough* OOP) leave no room for you to make this decision. Of course you put the netcode inside the object! Its data is private, so you'll have to write an interface to access it anyway. Might as well put all the smarts in there too. Conclusion I'm not saying you should write netcode like I do; only that this approach has worked for me so far. Read the code and judge for yourself. There is an objectively optimal approach for each use case, although people may disagree on which one it is. You should be free to choose based on actual constraints rather than arbitrary ones set forth by some paradigm. Thanks for reading. DECEIVER is launching on Kickstarter soon. Sign up to play the demo here! 0 comments 18. On the 2nd of November 2017 we launched a Kickstarter campaign for our game Nimbatus - The Space Drone Constructor, which aimed to raise$20,000. By the campaign’s end, 3000 backers had supported us with a total of $74,478. All the PR and marketing was handled by our indie developer team of four people with a very low marketing budget. Our team decided to go for a funding goal we were sure we could reach and extend the game’s content through stretch goals. The main goal of the campaign was to raise awareness for the game and raise funds for the alpha version. Part 1 - Before Launch Is what we believed when we launched our first Kickstarter campaign in 2016. For this first campaign, we had built up a very dedicated group of people before the Kickstarter’s launch. Nimbatus also had a bit of a following before the campaign launched: ~ 300 likes on Facebook ~ 1300 followers on Twitter ~ 1000 newsletter subs ~ 3500 followers on Steam However, there had been little interaction between players and us previous to the campaign's launch. This made us unsure whether or not the Nimbatus Kickstarter would reach its funding goal. A few weeks prior to launch, we started to look for potential ways to promote Nimbatus during the Kickstarter. We found our answer in social news sites. Reddit, Imgur and 9gag all proved to be great places to talk about Nimbatus. More about this in Part 3 - During the campaign. As with our previous campaign, the reward structure and trailer were the most time-consuming aspects of the page setup. We realised early that Nimbatus looks A LOT better in motion and therefore decided that we should show all features in action with animated GIFs. Two examples: In order to support the campaigns storytelling, “we built a ship, now we need a crew!”, we named all reward tiers after open positions on the ship. We were especially interested how the “Navigator” tier would do. This$95 tier would give backers free digital copies of ALL games our company EVER creates.   We decided against Early Bird and Kickstarter exclusive rewards in order avoid splitting backers into “winners and losers”, based on the great advice from Stonemaier Game’s book A Crowdfunder’s Strategy Guide (EDS Publications Ltd. (2015). Their insights also convinced us to add a $1 reward tier because it lets people join the update loop to build up trust in our efforts. Many of our$1 backers later increased their pledge to a higher tier. Two of our reward tiers featured games that are similar to Nimbatus. The keys for these games were provided by fellow developers. We think that this is really awesome and it helped the campaign a lot! A huge thanks to Avorion, Reassembly , Airships and Scrap Galaxy <3   Youtubers and streamers are important allies for game developers. They are in direct contact with potential buyers/backers and can significantly increase a campaign’s reach. We made a list of content creators who’d potentially be interested in our game. They were selected mostly by browsing Youtube for “let’s play” videos of games similar to Nimbatus. We sent out a total of 100 emails, each with a personalized intro sentence, no money involved. Additionally, we used Keymailer . Keymailer is a tool to contact Youtubers and streamers. At a cost of $150/month you can filter all available contacts by games they played and genres they enjoy. We personalized the message for each group. Messages automatically include an individual Steam key. With this tool, we contacted over 2000 Youtubers/Streamers who are interested in similar games. How it turned out - About 10 of the 100 Youtubers we contacted manually ended up creating a video/stream during the Kickstarter. Including some big ones with 1 million+ subscribers. - Over 150 videos resulted from the Keymailer outreach. Absolutely worth the investment! Another very helpful tool to find Youtubers/Streamers is Twitter. Before, but also during the campaign we sent out tweets , stating that we are looking for Youtubers/Streamers who want to feature Nimbatus. We also encouraged people to tag potentially interested content creators in the comments. This brought in a lot of interested people and resulted in a couple dozen videos. We also used Twitter to follow up when people where not responding via email, which proved to be very effective. In terms of campaign length we decided to go with a 34 day Kickstarter. The main reason being that we thought it would take quite a while until the word of the campaign spread enough. In retrospective this was ok, but we think 30 days would have been enough too. We were very unsure whether or not to release a demo of Nimbatus. Mainly because we were unsure if the game offered enough to convince players in this early state and we feared that our alpha access tier would potentially lose value because everyone could play already. Thankfully we decided to offer a demo in the end. More on this topic in Part 3 - During the campaign. Since we are based in Switzerland, we were forced to use CHF as our campaign’s currency. And while the currency is automatically re-calculated into$ for American backers, it was displayed in CHF for all other international backers. Even though CHF and $are almost 1:1 in value, we believed this to be a hurdle. There is no way to tell for us how many backers were scared away because of this in the end. Part 2: Kickstarter Launch We launched our Kickstarter campaign on a Thursday evening (UTC + 1) which is midday in the US. In order to celebrate the launch, we did a short livestream on Facebook. We had previously opened an event page and invited all our Facebook friends to it. Only a few people were watching and we were a bit stressed out. In order to help us spread the word we challenged our supporters with community goals. We promised that if all these goals were reached, each backer above$14 would receive an extra copy of Nimbatus. With most of the goals reached after the first week, we realized that we should have made the challenge a bit harder. The first few days went better than expected. We announced the Kickstarter on Imgur, Reddit, 9gag, Instagram, Facebook, Twitter, in some forums, via our Newsletter and on our Steam page. If you plan to release your game on Steam later on, we’d highly recommend that you set up your Steam page before the Kickstarter launches. Some people might not be interested in backing the game but will go ahead and wishlist it instead.   Part 3: During The Campaign We tried to keep the campaign’s momentum going. This worked our mostly thanks to the demo we had released. In order to download the Nimbatus demo, people needed to head over to our website and enter their email address. Within a few minutes, they received an automated email, including a download link for the demo. We used Mailchimp for this process.   We also added a big pop up in the demo to inform players about the Kickstarter. At first we were a bit reluctant to use this approach, it felt a bit sneaky. But after adding a line informing players they would be added to the newsletter and adding a huge unsubscribe button in the demo download mail, we felt that we could still sleep at night. For our previous campaign we had also released a demo. But the approach was significantly different. For the Nimbatus Kickstarter, we used the demo as a marketing tool to inform people about the campaign. Our previous Kickstarters’ demo was mainly an asset you could download if you were already checking out the campaign’s page and wanted to try the game before backing. We continued to frequently post on Imgur, Twitter, 9Gag and Facebook. Simultaneously, people streamed Nimbatus on Twitch and released videos on Youtube. This lead to a lot of demo downloads and therefore growth of our newsletter. A few hundred subs came in every day. Only about 10% of the people unsubscribed from the newsletter after downloading the demo.
Whenever we updated the demo or reached significant milestones in the campaign, such as being halfway to our goal, we sent out a newsletter. We also opened a Discord channel, which turned out a be a great way to stay in touch with our players. We were quite surprised to see a decent opening and link click rate. Especially if you compare this to our “normal” newsletter, which includes mostly people we personally met at events. Our normal newsletter took over two years to build up and includes about 4000 subs. With the Nimbatus demo, we gathered 50’000 subs within just 4 weeks and without travelling to any conferences.   (please note that around 2500 people subscribed to the normal newsletter during the Kickstarter) On the 7th day of the campaign we asked a friend if she would give us a shoutout on Reddit. She agreed and posted it in r/gaming. We will never forget what happened next. The post absolutely took off! In less than an hour, the post had reached the frontpage and continued to climb fast. It soon reached the top spot of all things on Reddit. Our team danced around in the office. Lots of people backed, a total of over $5000 came in from this post and we reached our funding goal 30 minutes after hitting the front page. We couldn’t believe our luck. Then, people started to accuse us of using bots to upvote the post. Our post was reported multiple times until the moderators took the post down. We were shocked and contacted them. They explained that they would need to investigate the post for bot abuse. A few hours later, they put the post back up and stated to have found nothing wrong with it and apologized for the inconvenience. Since the post had not received any upvotes in the past hours while it was taken down it very quickly dropped off the front page and the money flow stopped. While this is a misunderstanding we can understand and accept, people’s reactions hit us pretty hard. After the post was back up, many people on Reddit continued to accuse us and our friend. In the following days, our friend was constantly harassed when she posted on Reddit. Some people jumped over to our companies Twitter and Imgur account and kept on blaming us, asking if we were buying upvotes there too. It’s really not cool to falsely accuse people. Almost two weeks later we decided to start posting in smaller subreddits again. This proved to be no problem. But when we dared to do another post in r/gaming later, people immediately reacted very aggressive. We took the new post down and decided to stop posting in r/gaming (at least during the Kickstarter). After upgrading the demo with a new feature to easily export GIFs, we started to run competitions on Twitter. The coolest drones that were shared with #NimbatusGame would receive a free Alpha key for the game. Lots of players participated and helped to increase Nimbatus’ reach by doing so. We also gave keys to our most dedicated Youtubers/streamers who then came up with all kinds of interesting challenges for their viewers. All these activities came together in a nice loop: People downloaded the Nimbatus demo they heard about on social media/social news sites or from Youtubers/Streamers. By receiving newsletters and playing the demo they learned about the Kickstarter. Many of them backed and participated in community goals/competitions which brought in more new people. Not much happened in terms of press. RockPaperShotgun and PCGamer wrote articles, both resulting in about$500, which was nice. A handful of small sites picked up the news too. We sent out a press release when Nimbatus reached its funding goal, both to manually picked editors of bigger sites and via gamespress.com.   Part 4: Last Days Every person that hit the “Remind me” button on a Kickstarter page receives an email 48 hours before a campaign ends. This helpful reminder caused a flood of new pledges. We reached our last stretch goal a few hours before our campaign ended. Since we had already communicated this goal as the final one we withheld announcing any further stretch goals.   We decided to do a Thunderclap 24 hours before the campaign ends. Even after having done quite a few Thunderclaps, we are still unsure how big of an impact they have. A few minutes before the Kickstarter campaign was over we cleaned up our campaign page and added links to our Steam page and website. Note that Kickstarter pages cannot be edited after the campaign ends! The campaign ended on a Tuesday evening (UTC + 1) and raised a total of $75’000, which is 369% of the original funding goal. After finishing up our “Thank you” image and sending it to our backers it was time to rest. Part 5: Conclusion We are very happy with the campaign’s results. It was unexpected to highly surpass our funding goal, even though we didn’t have an engaged community when the campaign started. Thanks to the demo we were able to develop a community for Nimbatus on the go. The demo also allowed us to be less “promoty” when posting on social news sites. This way, interested people could get the demo and discover the Kickstarter from there instead of us having to ask for support directly when posting. This, combined with the ever growing newsletter, turned into a great campaign dynamic. We plan to use this approach again for future campaigns. Growth 300 ------------------> 430 Facebook likes 1300 -----------------> 2120 Twitter followers 1000 -----------------> 50’000 Newsletter signups 3500 -----------------> 10’000 Followers on Steam 0 ---------------------> 320 Readers of subreddit 0 ---------------------> 468 People on Discord 0 ---------------------> 300 Members in our forum More data 23% of our backers came directly from Kickstarter. 76% of our backers came from external sites. For our previous campaign it was 36/64. The average pledge amount of our backers was$26.
https://strayfawnstudio.com/
https://www.kickstarter.com/projects/strayfawnstudio/nimbatus-the-space-drone-constructor   Related Reading: Algo-Bot: Lessons Learned from our Kickstarter failure.
20. Original Post: Limitless Curiosity Out of various phases of the physics engine. Constraint Resolution was the hardest for me to understand personally. I need to read a lot of different papers and articles to fully understand how constraint resolution works. So I decided to write this article to help me understand it more easily in the future if, for example, I forget how this works. This article will tackle this problem by giving an example then make a general formula out of it. So let us delve into a pretty common scenario when two of our rigid bodies collide and penetrate each other as depicted below. From the scenario above we can formulate: We don't want our rigid bodies to intersect each other, thus we construct a constraint where the penetration depth must be more than zero. $$C: d>=0$$ This is an inequality constraint, we can transform it to a more simple equality constraint by only solving it if two bodies are penetrating each other. If two rigid bodies don't collide with each other, we don't need any constraint resolution. So: if d>=0, do nothing else if d < 0 solve C: d = 0 Now we can solve this equation by calculating  $$\Delta \vec{p1},\Delta \vec{p2},\Delta \vec{r1}$$,and  $$\Delta \vec{r2}$$  that cause the constraint above satisfied. This method is called the position-based method. This will satisfy the above constraint immediately in the current frame and might cause a jittery effect. A much more modern and preferable method that is used in Box2d, Chipmunk, Bullet and my physics engine is called the impulse-based method. In this method, we derive a velocity constraint equation from the position constraint equation above. We are working in 2D so angular velocity and the cross result of two vectors are scalars. Next, we need to find $$\Delta V$$ or impulse to satisfy the velocity constraint. This $$\Delta V$$ is caused by a force. We call this force 'constraint force'. Constraint force only exerts a force on the direction of illegal movement in our case the penetration normal. We don't want this force to do any work, contribute or restrict any motion of legal direction. $$\lambda$$ is a scalar, called Lagrangian multiplier. To understand why constraint force working on $$J^{T}$$ direction (remember J is a 12 by 1 matrix, so $$J^{T}$$ is a 1 by 12 matrix or a 12-dimensional vector), try to remember the equation for a three-dimensional plane. Now we can draw similarity between equation(1) and equation(2), where $$\vec{n}^{T}$$ is similar to J and $$\vec{v}$$ is similar to V. So we can interpret equation(1) as a 12 dimensional plane, we can conclude that $$J^{T}$$ as the normal of this plane. If a point is outside a plane, the shortest distance from this point to the surface is the normal direction. After we calculate the Lagrangian multiplier, we have a way to get back the impulse from equation(3). Then, we can apply this impulse to each rigid body. Baumgarte Stabilization Note that solving the velocity constraint doesn't mean that we satisfy the position constraint. When we solve the velocity constraint, there is already a violation in the position constraint. We call this violation position drift. What we achieve is stopping the two bodies from penetrating deeper (The penetration depth will stop growing). It might be fine for a slow-moving object as the position drift is not noticeable, but it will be a problem as the object moving faster. The animation below demonstrates what happens when we solve the velocity constraint. [caption id="attachment_38" align="alignnone" width="800"] So instead of purely solving the velocity constraint, we add a bias term to fix any violation that happens in position constraint.  So what is the value of the bias? As mentioned before we need this bias to fix positional drift. So we want this bias to be in proportion to penetration depth. This method is called Baumgarte Stabilization and $$\beta$$ is a baumgarte term. The right value for this term might differ for different scenarios. We need to tweak this value between 0 and 1 to find the right value that makes our simulation stable.   Sequential Impulse If our world consists only of two rigid bodies and one contact constraint. Then the above method will work decently. But in most games, there are more than two rigid bodies. One body can collide and penetrate with two or more bodies. We need to satisfy all the contact constraint simultaneously. For a real-time application, solving all these constraints simultaneously is not feasible. Erin Catto proposes a practical solution, called sequential impulse. The idea here is similar to Project Gauss-Seidel. We calculate $$\lambda$$ and $$\Delta V$$ for each constraint one by one, from constraint one to constraint n(n = number of constraint). After we finish iterating through the constraints and calculate $$\Delta V$$, we repeat the process from constraint one to constraint n until the specified number of iteration. This algorithm will converge to the actual solution.The more we repeat the process, the more accurate the result will be. In Box2d, Erin Catto set ten as the default for the number of iteration. Another thing to notice is that while we satisfy one constraint we might unintentionally satisfy another constraint. Say for example that we have two different contact constraint on the same rigid body. When we solve $$\dot{C1}$$, we might incidentally make $$\dot{d2} >= 0$$. Remember that equation(5), is a formula for $$\dot{C}: \dot{d} = 0$$ not $$\dot{C}: \dot{d} >= 0$$. So we don't need to apply it to $$\dot{C2}$$ anymore. We can detect this by looking at the sign of $$\lambda$$. If the sign of $$\lambda$$ is negative, that means the constraint is already satisfied. If we use this negative lambda as an impulse, it means we pull it closer instead of pushing it apart. It is fine for individual $$\lambda$$ to be negative. But, we need to make sure the accumulation of $$\lambda$$ is not negative. In each iteration, we add the current lambda to normalImpulseSum. Then we clamp the normalImpulseSum between 0 and positive infinity. The actual Lagrangian multiplier that we will use to calculate the impulse is the difference between the new normalImpulseSum and the previous normalImpulseSum Restitution Okay, now we have successfully resolve contact penetration in our physics engine. But what about simulating objects that bounce when a collision happens. The property to bounce when a collision happens is called restitution. The coefficient of restitution denoted $$C_{r}$$, is the ratio of the parting speed after the collision and the closing speed before the collision. The coefficient of restitution only affects the velocity along the normal direction. So we need to do the dot operation with the normal vector. Notice that in this specific case the $$V_{initial}$$ is similar to JV. If we look back at our constraint above, we set $$\dot{d}$$ to zero because we assume that the object does not bounce back($$C_{r}=0$$).So, if $$C_{r} != 0$$, instead of 0, we can modify our constraint so the desired velocity is $$V_{final}$$. We can merge our old bias term with the restitution term to get a new bias value. // init constraint // Calculate J(M^-1)(J^T). This term is constant so we can calculate this first for (int i = 0; i < constraint->numContactPoint; i++) { ftContactPointConstraint *pointConstraint = &constraint->pointConstraint; pointConstraint->r1 = manifold->contactPoints.r1 - (bodyA->transform.center + bodyA->centerOfMass); pointConstraint->r2 = manifold->contactPoints.r2 - (bodyB->transform.center + bodyB->centerOfMass); real kNormal = bodyA->inverseMass + bodyB->inverseMass; // Calculate r X normal real rnA = pointConstraint->r1.cross(constraint->normal); real rnB = pointConstraint->r2.cross(constraint->normal); // Calculate J(M^-1)(J^T). kNormal += (bodyA->inverseMoment * rnA * rnA + bodyB->inverseMoment * rnB * rnB); // Save inverse of J(M^-1)(J^T). pointConstraint->normalMass = 1 / kNormal; pointConstraint->positionBias = m_option.baumgarteCoef * manifold->penetrationDepth; ftVector2 vA = bodyA->velocity; ftVector2 vB = bodyB->velocity; real wA = bodyA->angularVelocity; real wB = bodyB->angularVelocity; ftVector2 dv = (vB + pointConstraint->r2.invCross(wB) - vA - pointConstraint->r1.invCross(wA)); //Calculate JV real jnV = dv.dot(constraint->normal pointConstraint->restitutionBias = -restitution * (jnV + m_option.restitutionSlop); } // solve constraint while (numIteration > 0) { for (int i = 0; i < m_constraintGroup.nConstraint; ++i) { ftContactConstraint *constraint = &(m_constraintGroup.constraints); int32 bodyIDA = constraint->bodyIDA; int32 bodyIDB = constraint->bodyIDB; ftVector2 normal = constraint->normal; ftVector2 tangent = normal.tangent(); for (int j = 0; j < constraint->numContactPoint; ++j) { ftContactPointConstraint *pointConstraint = &(constraint->pointConstraint[j]); ftVector2 vA = m_constraintGroup.velocities[bodyIDA]; ftVector2 vB = m_constraintGroup.velocities[bodyIDB]; real wA = m_constraintGroup.angularVelocities[bodyIDA]; real wB = m_constraintGroup.angularVelocities[bodyIDB]; //Calculate JV. (jnV = JV, dv = derivative of d, JV = derivative(d) dot normal)) ftVector2 dv = (vB + pointConstraint->r2.invCross(wB) - vA - pointConstraint->r1.invCross(wA)); real jnV = dv.dot(normal); //Calculate Lambda ( lambda real nLambda = (-jnV + pointConstraint->positionBias / dt + pointConstraint->restitutionBias) * pointConstraint->normalMass; // Add lambda to normalImpulse and clamp real oldAccumI = pointConstraint->nIAcc; pointConstraint->nIAcc += nLambda; if (pointConstraint->nIAcc < 0) { pointConstraint->nIAcc = 0; } // Find real lambda real I = pointConstraint->nIAcc - oldAccumI; // Calculate linear impulse ftVector2 nLinearI = normal * I; // Calculate angular impulse real rnA = pointConstraint->r1.cross(normal); real rnB = pointConstraint->r2.cross(normal); real nAngularIA = rnA * I; real nAngularIB = rnB * I; // Apply linear impulse m_constraintGroup.velocities[bodyIDA] -= constraint->invMassA * nLinearI; m_constraintGroup.velocities[bodyIDB] += constraint->invMassB * nLinearI; // Apply angular impulse m_constraintGroup.angularVelocities[bodyIDA] -= constraint->invMomentA * nAngularIA; m_constraintGroup.angularVelocities[bodyIDB] += constraint->invMomentB * nAngularIB; } } --numIteration; }   General Step to Solve Constraint In this article, we have learned how to solve contact penetration by defining it as a constraint and solve it. But this framework is not only used to solve contact penetration. We can do many more cool things with constraints like for example implementing hinge joint, pulley, spring, etc. So this is the step-by-step of constraint resolution: Define the constraint in the form $$\dot{C}: JV + b = 0$$. V is always $$\begin{bmatrix} \vec{v1} \\ w1 \\ \vec{v2} \\ w2\end{bmatrix}$$ for every constraint. So we need to find J or the Jacobian Matrix for that specific constraint. Decide the number of iteration for the sequential impulse. Next find the Lagrangian multiplier by inserting velocity, mass, and the Jacobian Matrix into this equation: Do step 3 for each constraint, and repeat the process as much as the number of iteration. Clamp the Lagrangian multiplier if needed. This marks the end of this article. Feel free to ask if something is still unclear. And please inform me if there are inaccuracies in my article. Thank you for reading. NB: Box2d use sequential impulse, but does not use baumgarte stabilization anymore. It uses full NGS to resolve the position drift. Chipmunk still use baumgarte stabilization. References Allen Chou's post on Constraint Resolution A Unified Framework for Rigid Body Dynamics An Introduction to Physically Based Modeling: Constrained Dynamics Erin Catto's Box2d and presentation on constraint resolution Falton Debug Visualizer 18_01_2018 22_40_12.mp4 equation.svg
By kevinyu

## GameDev Contractors

1. Experience freelance developer of over 15 years. Worked on various games using engines such as Unity and Unreal. Previous releases have been published on Steam and app stores. Recent projects include games developed on the Ethereum blockchain and a 3D music software: http://store.steampowered.com/app/673730/Aurrery/ https://github.com/markfrance Available to develop games using a wide range of technologies. info@blockchain-games.io
2. Hi, I'm an industry professional with a decade of freelancing experience. I specialize in projects that seek further funding through the creation of a demo/prototype/POC and have a limited budget. I've worked on a number of highlight projects in the past and deliberately choose to focus on indie projects now. If you have a great idea but are lacking a developer that can put it together, look no further! I'll even help you pitch through crowdfunding or publishers! https://www.linkedin.com/in/michelmony/ Cheers!
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