[pygame] Re: BOUNCE pygame-users@seul.org: Non-member submission from [MarkusBopp <markus.bopp@smail.inf.fh-bonn-rhein-sieg.de>]

[Pete Shinners <pete@shinners.org>]

> I have a problem with checking rects overlapping.
> I use this slow procedure to test if collision works:
>
> for shot in shotlist:
>           for opp in opplist:
>                 print opp.img.get_rect().colliderect( shot.img.get_rect() )
>
> the problem is that colliderect always returns the index '1' although no 
> rects overlapped.
i assume you are not worried about optimizing this collision detection 
for now, but there is a lot of simple work you can do for this 'slow 
procedure'.

your problem is you are checking for collision against the image 
rectangles. image rectangles always start at (0, 0) and have width and 
height the same as the image. your image rectangles will always 
overlap (unless perhaps one image is sized 0? but i don't believe SDL 
allows that)

it's likely your objects have some sort of position attribute. if that 
represents the topleft corner your code should look more like this

  for shot in shotlist:
      shotrect = shot.img.get_rect().move(shot.position)
      for opp in opplist:
          opprect = opp.img.get_rect().move(opp.position)
          print opprect.colliderect(shotrect)

the bad news is that this will be even a bit slower. the good news is 
it's almost easier to optimize for more speed.