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06.24.2003 at 09:42AM PDT, ID: 20658459

	[x] Attachment Details

Calculating reflection vector

[x]

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6.4

Zone:

Physics & Artificial Intelligence in Game Programming

Tags:

vector, reflection

I'm hoping my question ends up being very simple to answer, yet it troubles me a lot.

I have two 2D direction vectors A and B.

All I want to do is calculate the a new direction for vector A based on how it would reflect or "bounce" when hit on vector B. Imagine a ball hitting a wall, if you will, to get the basic idea. 2D. A and B are sometimes paraller with the X or Y planes, sometimes not.

Now, here's the trick. I've been using an algorithm often mentioned in the tutorials around the net:

R = V - ( 2 * V [dot] N ) N

(V = vector A, N = vector B, [dot] stands for dot product)

However, I've noticed some occassions where this algorithm does not work, here is an example of one: http://www.infire.com/vectorproblem.gif

I'd like to either find out what am I doing wrong on calculating the reflection or in case the whole algorithm is faulty, find out how to really calculate the angle so that it works every single time.

I've also tried another algorithm, R = 2 ( V [dot] N ) N - V. This works fine on that example above, but it's faulty on another occassion: http://www.infire.com/vectorproblem2.gif

Of course, now that I think of it, maybe I really am doing something drastically wrong... Please tell me what. Points to person who can give me an algorthm or -even better- pseudo code for calculating this thing.

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