Hey All,

I'm having some issues with my collision response for a breakout style game. Currently my circle (ball) to rectangle (bricks/paddle) detection works fine, however the response is acting odd. Engine used is SFML.

I searched up the vector reflection equation, however I think I may be implementing it wrong (particularly the normal).



Where n is the normal of the plane and u is the incident vector.

Here is my code implementation:



I believe I may be caclulating the normal wrong, however I havn't been able to find any defnitive formulas.

Currently upon a collision with the paddle, the ball will bounce in an upwards direction, continuing this until it is moving perfectly up and down. Playing around with the equation etc just causes the ball to bounce back in the direction it came, although at a slightly different angle. Any ideas on how to implement correct circle-rectangle collision response?

Sorry if I havn't posted enough code etc, first time asking on a forum for programming help.

Thanks, Jmatt.

Off to Game Programming.

Have you tried using this:



From the formula you gave, ballVel would be u and paddlePos.normalise would be n. If you look at the formula. Taking the formula and substituting the above would give you the above code.

This post has been edited by SixOfEleven: 4 Jul, 2009 - 06:22 AM

As far as the actual math is concerned, if you need the normal of two vectors, calculate a cross product, if you need the normal of one 2D vector, use a negative reciprocal

Using that formula just causes to ball to jump randomly accross the screen.

So are you trying to find the velocity of the ball after its reflection with the paddle?

If so, you don't need the normal

This post has been edited by jyth: 4 Jul, 2009 - 07:42 PM

No, i'm trying to calculate the reflection.

What do you mean by the reflection? the angle?

I want to reflect the vector that the ball is coming in at, so that it bounces off the paddle at the opposite that it came in at. For now I've just reversed the y of the vector, however this fails when hitting the sides of the paddle. Eventually I'd like to get the ball bouncing off at different angles depending upon where it collides.

You can work out the angle of collision like this
dx = velocity * cos(angle)
dy = velocity * sin(angle)

the bounce would be like this
dx = -dx;

Work out the velocity and angle like this


Hope this helps a little

*edit* Code Tags

This post has been edited by stayscrisp: 5 Jul, 2009 - 08:24 AM