Collision detection for irregular shaped objects.

[Dar Scott]

On Thursday, April 11, 2002, at 05:32 AM, malte brill wrote:

> I want to check if objects on my stack collide.
> I got two PNG Images including Alpha Channels on my stack, the 
> second one
> placed in a distance of 100 pixels or so under the first one.

Consider this.  It might be a little naive and slow, so if this is 
for a game you may need to come up with a way to speed this up.  
This is for images only.

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If they don't overlap, they don't collide.

Otherwise, calculate the overlap rectangle.

For pixels in the overlap check to see if the opacity of the pixel 
in one image and that of the corresponding pixel in the other image 
indicate collision.  (Say, add to over 100% opacity.)  If all 
pixels are checked and none collide, then the images do not collide.

If any pixel collides, quit the check; the images collide.
********

Use the alphaData property of the images to get the alphaData 
info.  It is a string of bytes, so you have to do some math to pull 
out the right byte for each pixel.

Alternately, if the images are of circles or perhaps some other 
simple regular shape, then a simple model of the shape can be used 
to check collision.

Dar Scott