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Xref: csiph.com comp.lang.python:44697

On 03/05/2013 23:23, Alex Gardner wrote:
> When rect A collides with rect B they stick when I am wanting A to bounce off of B.  I have tried different methods, but none seem to work.  My source is here:  http://pastebin.com/CBYPcubL
>
> The collision code itself is below:
> ------
> # Bounce off of the paddle
> if paddle_rect.colliderect(ball_rect):
>      y_vel*=-1
>      x_vel*=-1
>
Apart from the other comments, I'm not sure about this line:

     y_vel = (math.fabs(2 - x_vel)**2) ** .5

Firstly, instead of math.fabs you could use abs:

     y_vel = (abs(2 - x_vel)**2) ** .5

Then again, you're squaring the result, and the square of (2 - x_vel)
will always be positive anyway:

     y_vel = ((2 - x_vel)**2) ** .5

You're also calculating getting the square root, for which math.sqrt 
would be simpler:

     y_vel = math.sqrt((2 - x_vel)**2)

Then again, you're calculating the square root of a squared number, so
you might as well just write:

     y_vel = abs(2 - x_vel)