I'm still not entirely sure about the interface I want to provide. The problem is computing the corresponding rects. Let's say you have an obstacle with rect a and are dragging an object with rect b. Then the output should have rect c where
c.top = a.top - b.bottom c.bottom = a.bottom - b. top c.left = a.left - b.right c.right = a.right - b.left(this might be off-by-one somewhere..probably need a -1 in c.bottom and c.left). This would mean the bit of c corresponding to (x,y) would be set if b were translated by (x,y). The reason this all presents a problem is because masks don't have associated rects, but I'd rather not leave it to the user to do the math. Probably the right thing to do is provides something that takes a pair of sprites with rect and mask fields and outputs a sprite.
The other problem is that for my application I'd like to apply this to many sprites all at once and then compute the overlay. It would be more efficient to compute this all in one go since the intermediate masks could be avoided. Probably the right thing then is to provide a function to compute the hitmask of a whole sprite group.
So I guess I've answered my own question. The interface should consist of two functions:
hitmask(Sprite) :: Sprite Return a sprite with the rect and mask attributes set grouphitmask(Group) :: Sprite Return a sprite with the rect and mask attributes set, containing the union of the hitmasks for the group
What do you think? Also, if you do want me to add this to pygame, should it go in the mask module or the sprite module?
--Mike Nirav Patel wrote:
Mike Ah, very interesting. Can I see the source on that? I would love to see that included in the Mask module. Nirav