• 13
• 15
• 27
• 9
• 9
• ### Similar Content

• By abarnes
Hello All!
I am currently pursuing a degree in video game programming, so far I have completed an intro to programming course and object oriented programming course. Both were taught using C++ as the programming langauge which I know is very popular for game development, but in these classes we do not actually do any game development. I would like to start to build my skills with C++ for game development as that is a common required thing for a job and am looking for ways to do this. Any recommendations such as books to read or youtube videos to watch will be greatly appreciated!
• By Orella
I'm having problems rotating GameObjects in my engine. I'm trying to rotate in 2 ways.
I'm using MathGeoLib to calculate maths in the engine.
First way: Rotates correctly around axis but if I want to rotate back, if I don't do it following the inverse order then rotation doesn't work properly.
e.g:
Rotate X axis 50 degrees, Rotate Y axis 30 degrees -> Rotate Y axis -50 degrees, Rotate X axis -30 degrees. Works.
Rotate X axis 50 degrees, Rotate Y axis 30 degrees -> Rotate X axis -50 degrees, Rotate Y axis -30 degrees. Doesn't.

Code:
void ComponentTransform::SetRotation(float3 euler_rotation) { float3 diff = euler_rotation - editor_rotation; editor_rotation = euler_rotation; math::Quat mod = math::Quat::FromEulerXYZ(diff.x * DEGTORAD, diff.y * DEGTORAD, diff.z * DEGTORAD); quat_rotation = quat_rotation * mod; UpdateMatrix();  } Second way: Starts rotating good around axis but after rotating some times, then it stops to rotate correctly around axis, but if I rotate it back regardless of the rotation order it works, not like the first way.

Code:
void ComponentTransform::SetRotation(float3 euler_rotation) { editor_rotation = euler_rotation; quat_rotation = math::Quat::FromEulerXYZ(euler_rotation.x * DEGTORAD, euler_rotation.y * DEGTORAD, euler_rotation.z * DEGTORAD); UpdateMatrix();  }
Rest of code:
#define DEGTORAD 0.0174532925199432957f void ComponentTransform::UpdateMatrix() { if (!this->GetGameObject()->IsParent()) { //Get parent transform component ComponentTransform* parent_transform = (ComponentTransform*)this->GetGameObject()->GetParent()->GetComponent(Component::CompTransform); //Create matrix from position, rotation(quaternion) and scale transform_matrix = math::float4x4::FromTRS(position, quat_rotation, scale); //Multiply the object transform by parent transform transform_matrix = parent_transform->transform_matrix * transform_matrix; //If object have childs, call this function in childs objects for (std::list<GameObject*>::iterator it = this->GetGameObject()->childs.begin(); it != this->GetGameObject()->childs.end(); it++) { ComponentTransform* child_transform = (ComponentTransform*)(*it)->GetComponent(Component::CompTransform); child_transform->UpdateMatrix(); } } else { //Create matrix from position, rotation(quaternion) and scale transform_matrix = math::float4x4::FromTRS(position, quat_rotation, scale); //If object have childs, call this function in childs objects for (std::list<GameObject*>::iterator it = this->GetGameObject()->childs.begin(); it != this->GetGameObject()->childs.end(); it++) { ComponentTransform* child_transform = (ComponentTransform*)(*it)->GetComponent(Component::CompTransform); child_transform->UpdateMatrix(); } } } MathGeoLib: Quat MUST_USE_RESULT Quat::FromEulerXYZ(float x, float y, float z) { return (Quat::RotateX(x) * Quat::RotateY(y) * Quat::RotateZ(z)).Normalized(); } Quat MUST_USE_RESULT Quat::RotateX(float angle) { return Quat(float3(1,0,0), angle); } Quat MUST_USE_RESULT Quat::RotateY(float angle) { return Quat(float3(0,1,0), angle); } Quat MUST_USE_RESULT Quat::RotateZ(float angle) { return Quat(float3(0,0,1), angle); } Quat(const float3 &rotationAxis, float rotationAngleRadians) { SetFromAxisAngle(rotationAxis, rotationAngleRadians); } void Quat::SetFromAxisAngle(const float3 &axis, float angle) { assume1(axis.IsNormalized(), axis); assume1(MATH_NS::IsFinite(angle), angle); float sinz, cosz; SinCos(angle*0.5f, sinz, cosz); x = axis.x * sinz; y = axis.y * sinz; z = axis.z * sinz; w = cosz; } Any help?
Thanks.
• By owenjr
Hi there!
I am trying to implement a basic AI for a Turrets game in SFML and C++ and I have some problems.
This AI follows some waypoints stablished in a Bezier Courve.
In first place, this path was followed only by one enemy. For this purpose, the enemy has to calculate his distance between his actual position
to the next waypoint he has to pick.
If the distance is less than a specific value we stablish, then, we get to the next point. This will repeat until the final destination is reached. (in the submitting code, forget about the var m_go)

Okay, our problem gets when we spawn several enemies and all have to follow the same path, because it produces a bad visual effect (everyone gets upside another).
In order to solve this visual problem, we have decided to use a repulsion vector. The calculus gets like this:

As you can see, we calculate the repulsion vector with the inverse of the distance between the enemy and his nearest neighbor.
Then, we get it applying this to the "theorical" direction, by adding it, and we get a resultant, which is the direction that
our enemy has to follow to not "collide" with it's neighbors. But, our issue comes here:

The enemys get sepparated in the middle of the curve and, as we spawn more enemys, the speed of all of them increases dramatically (including the enemies that don't calculate the repuslion vector).
1 - Is it usual that this sepparation occours in the middle of the trajectory?
2 - Is it there a way to control this direction without the speed getting affected?
3 - Is it there any alternative to this theory?

I submit the code below (There is a variable in Spanish [resultante] which it means resultant in English):

if (!m_pathCompleted) { if (m_currentWP == 14 && m_cambio == true) { m_currentWP = 0; m_path = m_pathA; m_cambio = false; } if (m_neighbors.size() > 1) { for (int i = 0; i < m_neighbors.size(); i++) { if (m_enemyId != m_neighbors[i]->GetId()) { float l_nvx = m_neighbors[i]->GetSprite().getPosition().x - m_enemySprite.getPosition().x; float l_nvy = m_neighbors[i]->GetSprite().getPosition().y - m_enemySprite.getPosition().y; float distance = std::sqrt(l_nvx * l_nvx + l_nvy * l_nvy); if (distance < MINIMUM_NEIGHBOR_DISTANCE) { l_nvx *= -1; l_nvy *= -1; float l_vx = m_path[m_currentWP].x - m_enemySprite.getPosition().x; float l_vy = m_path[m_currentWP].y - m_enemySprite.getPosition().y; float l_resultanteX = l_nvx + l_vx; float l_resultanteY = l_nvy + l_vy; float l_waypointDistance = std::sqrt(l_resultanteX * l_resultanteX + l_resultanteY * l_resultanteY); if (l_waypointDistance < MINIMUM_WAYPOINT_DISTANCE) { if (m_currentWP == m_path.size() - 1) { std::cout << "\n"; std::cout << "[GAME OVER]" << std::endl; m_go = false; m_pathCompleted = true; } else { m_currentWP++; } } if (l_waypointDistance > MINIMUM_WAYPOINT_DISTANCE) { l_resultanteX = l_resultanteX / l_waypointDistance; l_resultanteY = l_resultanteY / l_waypointDistance; m_enemySprite.move(ENEMY_SPEED * l_resultanteX * dt, ENEMY_SPEED * l_resultanteY * dt); } } else { float vx = m_path[m_currentWP].x - m_enemySprite.getPosition().x; float vy = m_path[m_currentWP].y - m_enemySprite.getPosition().y; float len = std::sqrt(vx * vx + vy * vy); if (len < MINIMUM_WAYPOINT_DISTANCE) { if (m_currentWP == m_path.size() - 1) { std::cout << "\n"; std::cout << "[GAME OVER]" << std::endl; m_go = false; m_pathCompleted = true; } else { m_currentWP++; } } if (len > MINIMUM_WAYPOINT_DISTANCE) { vx = vx / len; vy = vy / len; m_enemySprite.move(ENEMY_SPEED * vx * dt, ENEMY_SPEED * vy * dt); } } } } } else { float vx = m_path[m_currentWP].x - m_enemySprite.getPosition().x; float vy = m_path[m_currentWP].y - m_enemySprite.getPosition().y; float len = std::sqrt(vx * vx + vy * vy); if (len < MINIMUM_WAYPOINT_DISTANCE) { if (m_currentWP == m_path.size() - 1) { std::cout << "\n"; std::cout << "[GAME OVER]" << std::endl; m_go = false; m_pathCompleted = true; } else { m_currentWP++; } } if (len > MINIMUM_WAYPOINT_DISTANCE) { vx = vx / len; vy = vy / len; m_enemySprite.move(ENEMY_SPEED * vx * dt, ENEMY_SPEED * vy * dt); } } }
¡¡Thank you very much in advance!!

• 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 After cloning, an $ORX environment variable will be created automatically for your system which will help with making game projects much easier. It will also create several IDE projects for your operating system: Visual Studio, Codelite, Code::Blocks, and gmake. These Orx projects will allow you to compile the Orx library for use in your own projects. And the$ORX environment variable means that your projects will know where to find the Orx library.
For more details on this step, visit http://orx-project.org/wiki/en/tutorials/cloning_orx_from_github at the Orx learning wiki.
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.

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.
• By yyam

Hey there! I released my game, Hedgehogs Can Fly, on GameJolt today! It's a cute, 2D physics-platformer where you try to fling a hedgehog through tricky levels to get to the finish line. I wrote it from scratch in C++ with SFML. There are multiple types of terrain each with different properties and effects making for some interesting level design. The physics/level code also allows for free-form terrain that isn't constrained to a tile grid. The levels are loaded from color-coded image files, I have an entry in the devlog on the GameJolt page explaining how it all works!
If these screenshots look cool, visit the GameJolt page here (With Trailer Video!)
Screenshots incoming...

Have a nice day

# Dividing things up and adding things back together precision problems

## Recommended Posts

I'm trying to find a good precise numeric solution for my problem.

Background:

I'm trying to create a trade simulation between cities. Each demands a certain amount of a resource and may have a certain number of importers cities that provide that resource. A city needs to take an equal fraction of each importer's resources, and the sum of the amounts taken must add up to the amount demanded. For example, if a city demands 2 bushels of grain, and has three importers, it will take 2/3 of the resources form each importer city, and the sum must add up to 2. Cities will always produce and demand an integer amount of goods, but a city may export to multiple places, so the amount of goods available may be a rational number. At no point are irrational numbers needed.

Limitations:

I'm working in C++ and emscripten. This means I cannot link any library to my project; I must include the whole source. For this reason, I'd prefer not to include any large library. I don't want to use boost. This is a closed source project, so I can't use anything GPL.

Options:

1) Use floating point with an epsilon. But I'm not sure how to pick the right epsilon here. This reproach has the advantage of being fast and simple though.

2) Use fixed point. If I use scaling factor that's a multiple or several lowest factors, it may be precise. But I need to ensure that any numerator of my fractions is a factor of the scaling factor. I'm not sure if I can ensure this. But if a city imports from at most N cites, and the scaling factor is N!, maybe this could work? or some version of it?

3) Use rational numbers. This ensure that calculations are precise all around. If I implement this myself, this is the most complex option.

I'm wondering if anyone here has any suggestions as to which is the best option for my use case, and if there are any libraries I might be able to use.

Edited by King Mir

##### Share on other sites

I would go with "3) Use rational numbers". If your numbers don't get out of whack and you can just use 64 bits for numerator and denominator, the code shouldn't be too bad.

##### Share on other sites

Thanks for the feedback.

Note do to limitations of how I'm compiling this, I can't use 64 bit integers. I can use 32 bit integers or doubles (which are precise up to 52 bits).

##### Share on other sites

You can write a little class that acts like a "large integer", but wraps around two 32-bit integers. Then you can carefully perform integer arithmetic as if you were using a 64-bit integer. I've seen this done before in older games.

Then you can use two of these "large integers" to represents an irrational number.

Edited by Randy Gaul

##### Share on other sites
5 hours ago, King Mir said:

if a city demands 2 bushels of grain, and has three importers, it will take 2/3 of the resources form each importer city, and the sum must add up to 2. Cities will always produce and demand an integer amount of goods, but a city may export to multiple places, so the amount of goods available may be a rational number. At no point are irrational numbers needed.

I don't see why you need floating point numbers for this at all.

You've got N products and M targets.  Do an integer divide and mod, assign accordingly.

For example, 10 products among 4 cities gives 2 for each, plus 2 remainder. Top two cities are assigned 3, the rest assigned 2.   Or 73 resources among 5 cities, 3 cities assigned 15, two are assigned 14.

Alternatively, if resources travel in smaller packets, draw from all sources until you've got what you need.  If one source runs out early you'll still be drawing from others until the need is satisfied.

Drawing from all in smaller units also helps when resources may be limited, or when they may change over the time it takes for goods to be transported in the game's simulation. (I'm particularly thinking of games where transporters travel to the location, pick up a bundle of resources, and travel to the destination, repeating until all the bundles are transferred.  Consider the 73 being 15/15/15/14/14 example, if you've got one source that only has 3 of the resources, you'll just keep drawing resources from all the cities until the need is satisfied even if cities run out.  It shows up as an unsatisfied need rather than a demand for a specific number from each location.

##### Share on other sites
4 minutes ago, frob said:

I don't see why you need floating point numbers for this at all.

You've got N products and M targets.  Do an integer divide and mod, assign accordingly.

For example, 10 products among 4 cities gives 2 for each, plus 2 remainder. Top two cities are assigned 3, the rest assigned 2.   Or 73 resources among 5 cities, 3 cities assigned 15, two are assigned 14.

Alternatively, if resources travel in smaller packets, draw from all sources until you've got what you need.  If one source runs out early you'll still be drawing from others until the need is satisfied.

Drawing from all in smaller units also helps when resources may be limited, or when they may change over the time it takes for goods to be transported in the game's simulation. (I'm particularly thinking of games where transporters travel to the location, pick up a bundle of resources, and travel to the destination, repeating until all the bundles are transferred.  Consider the 73 being 15/15/15/14/14 example, if you've got one source that only has 3 of the resources, you'll just keep drawing resources from all the cities until the need is satisfied even if cities run out.  It shows up as an unsatisfied need rather than a demand for a specific number from each location.

The problem with that is, which cities do I take the remainder from? It can matter because it effects the resources available to be exported to other cities. I could add a priority to importers, but that would be adding interface complexity. In short, it would be different algorithm to do it that way.

I don't plan to have transport delays; the timescale of the game is in years.

##### Share on other sites

You'd have to make that decision no matter what route you took.  Unless it was always exactly divisible there would always be a mismatch.

Maybe pick them randomly through a shuffle or similar, maybe pick them based on some priority like how much the city produces or the number of resource the city is exporting in total, maybe always pick the first ones on the list that was passed to them, maybe let the player choose.

##### Share on other sites

So if you're interested, here's the algorithm I'm using in some detail:

	For each city, A, (in an order that is complex to go into -- this isn't really a for loop but a recursive graph traversal)
needs = demand of this city + all cities it exports to
available = surplus of all importers added together
For each city, B, that imports to A
city_available = (production of B)  - (all the previously calculated exports of B)
if needs < available
import ( (city_available / available) * needs  ) resources
else
import (city_available) resources
(Then calculate how much each city that city A exports to gets -- I haven't done this part yet)


The outer order requires that cities have a priority of who they export to. For example a city would choose to export first to London, then everything that's left goes to Canterbury. But London is not going to prefer where its goods come from; demand is equal on all importers, and all of them end up with surplus if they can't pass it on their excess to Canterbury.

Now I wish I could get rid of the need to have export priorities, but I'm pretty sure that would make the whole calculation a way too complex differential equation.

As you can see, this takes an equal amount from each importer, even if it's a fractional amount; no remainder.

##### Share on other sites

It's probably a good idea to think of your game design as if it were a board game, where you are using tokens to represent the goods, so you are forced to use small integers. Typical ways to break ties in board games involve some sort of turn order, so cities are sorted by some criterion (distance to London, size, foundation date...) and then if there is a remainder of 2 after integer division, the top 2 cities get an additional token.

If you don't want this mechanic to affect the game much, make the number of tokens large, so a difference of 1 token won't matter. It's probably not good to obsess over making things exact.

##### Share on other sites
On 8/22/2017 at 9:16 AM, alvaro said:

It's probably a good idea to think of your game design as if it were a board game, where you are using tokens to represent the goods, so you are forced to use small integers. Typical ways to break ties in board games involve some sort of turn order, so cities are sorted by some criterion (distance to London, size, foundation date...) and then if there is a remainder of 2 after integer division, the top 2 cities get an additional token.

If you don't want this mechanic to affect the game much, make the number of tokens large, so a difference of 1 token won't matter. It's probably not good to obsess over making things exact.

So the problem with "not obsessing over making things exact" is that that could encourage micromanagement, because a micromanaging player can manage better than the ai in that case. I would prefer a system that just works for player and ai alike.

That said, I'm not sure my current design squares up with that goal entirely; a player will be able to optimize by adjusting export priorities.