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Atari coding BBS
| Bitplane collision detect |
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Posted by: Simon Sunnyboy / Paradize
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Jul,27.2010-18:41
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Today I thought about how to detect a collision while drawing a sprite. E.q. have a bitplane (nr 4) in the background set and use this to indicate a collision (drawinging over color 8-15 should trigger a collision detection)
While drawing the sprite, the onscreen bitplane is obviously read and masked with AND. Now I wondered if there was a simple thing to implement as a sideeffect to detect a set pixel that is masked away.
A clumsy approach might look like this but it takes way too many cycles...
assume a0 points to screen, a1 to mask data
move.w (a0),d0 ; fetch bitplane and store temporarily
move.w (a1)+,d1 ; fetch mask data (pixels to keep are 1, pixels to clear to OR the sprite in are 0)
and.w d1,0(a0)+ ; mask onscreen
; now:
neg.w d1 ; flip mask bits
and.w d1,d0 ; and the negated mask with the bitplane
bne collision_found ; if any bit is still set we found a pixel based collision
Any ideas or suggestions? I am thinking of a generic approach here...
cheers,
ssb
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