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Atari coding BBS
| Blit OP Register |
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Posted by: Bod/STAX
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Aug,18.2013-22:43
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In my game the sprites that use the blitter are stored as a one plane mask and a four plane sprite. I set the blitter OP register to %0001 (source and target) to plot all masks in one go and then set it to %0111 (source or target) and then plot all sprite gfx in one go.
For all the sprites that requited >1 hit to be destroyed (such as the very large baddies) I had a seperate set of sprites that were exactly the same but were stored as four planes filled in to one colour.
Today I decided to save a bit of memory and maybe speed things up by letting the blitter do this. When a baddie with a >1 hit value is hit i turn off the gfx drawing routine and only plot the mask to the four planes but set the blit op register to %1101 (not source or target) which to me would do the same job but the sprites go flicker and somethimes a crash occours. Does the source get affected? to me what the blitter does here is take the each 16 pixels of the mask not it and or it to the target without affecting the mask.
Am I missing something here?
Why would all of a sudden flicker occour?
Thanks.
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