• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
Sign in to follow this  
Followers 0
Crovea

Rotating vector, need help!

6 posts in this topic

Hey!

I making a 2d top-down shooter game and i'm currently in the process of creating weapons.

When a soldier fires a projectile, i find the unit vector between the soldiers center and mouse position ( the target )
and use that as a basis for the velocity vector for the projectile which works fine!

But i've run into problems creating a shotgun, which is supposed to spray bullets.
What i want to do here is spread 5 bullets out evenly in a 25 degree angle centered around the target vector.

My vector math is a few too many years behind me but from what i've been able to find online, the formula i need and have been using is:

[CODE]
xVel = xVel * (float)cos(addingAngle) - yVel * (float)sin(addingAngle);
yVel = yVel * (float)sin(addingAngle) + yVel * (float)cos(addingAngle);
[/CODE]
Where xVel and yVel is the coordinates of the unit vector i found between shooter and target. addingAngle is the angle im trying to add ( or substract by being negative).

This is however, giving me some wierd results with bullets flying in irregulair angles.
I'm probably mixing up radians and degrees, but that doesnt explain why my bullets appear to be choosing such apparently random angles (however conistent)

So can anyone point me in the right direction?
I'm going to have to read up on vectors eventually, but i'd rather wait until i have more time on my hands.
0

Share this post


Link to post
Share on other sites
You've copied something a little carelessly, I think. You want:

[code]

xVel_new = xVel * (float)cos(addingAngle) - yVel * (float)sin(addingAngle);
yVel_new = xVel * (float)sin(addingAngle) + yVel * (float)cos(addingAngle);

xVel = xVel_new;
yVel = yVel_new;
[/code]

In addition to having to use separate variables (as the original values of both xVel and yVel are needed in each line of the calculation), there was an error in the first term on the second line.
0

Share this post


Link to post
Share on other sites
Thanks alot, this works perfectly it seems!

I copied it right from the formula i found:
http://stackoverflow.com/questions/6006400/modifying-the-angle-of-a-unit-vector

Which is kinda strange i think? I guess that could have something to do with the y-axis being inverted or something

I have no idea how i missed that the second line of code was using the first variable, which obviously causes errors xD
0

Share this post


Link to post
Share on other sites
Sorry, what's strange? What I put is a direct translation of those forumulas. Note that they assign to x' and y' (corresponding to xVel_new and yVel_new), not to x and y.
0

Share this post


Link to post
Share on other sites
The code in the link did have the mistake of using y instead of x in the first term of the second formula. The mistake of using the same variables (which many of us have made before) was introduced by the OP.
0

Share this post


Link to post
Share on other sites
One more thing: If instead of specifying a rotation as an angle you used a unit-length vector (cos(angle), sin(angle)), your code would be simpler in general. In the particular case of rotating a vector, the code would look like the multiplication of complex numbers. But the main advantages of using unit-length vectors instead of angles are:[list]
[*]Fewer special cases (like 360 becoming 0)
[*]More natural conversion to working in 3D (where rotations are represented with unit-length quaternions, instead of unit-length complex numbers).
[/list]
This might be a bit too mathematically sophisticated for you at this stage, but it's good to keep in mind that it's an option, in case you feel like exploring it at some point. Edited by alvaro
0

Share this post


Link to post
Share on other sites
[quote name='alvaro' timestamp='1339290080' post='4947793']
The code in the link did have the mistake of using y instead of x in the first term of the second formula.
[/quote]

Ah I see it now, I was only looking at the initial snippet of mathematics. My apologies.
0

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0