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Originally Posted by alain.treesong
EDIT : and of course the blitter which is dedicated to the characters can of course flip some images to manage the double direction
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Blitter can't flip horizontally, only vertically, and even that's not so easy when using interleaved bitplane mode... you have to do each bitplane seperately.
Flipping with the CPU is possible though, and could be done "ahead" of time... so when you trigger an animation sequence playing, the subsequent frames are flipped in advance into a buffer (could even be decompressed on the fly too... that's been talked about before with regards to this kind of game). Also masks need flipping too... this only needs to be done for one plane, and then the flipped data copied to the other planes. In fact, perhaps only one plane of mask needs storing anyway, and the full 4 plane massk can be constructed on the fly ahead of time too.
One thing that is definitely possible, is that the masks are not needed for one character... that character can be just blitted straight to the playfield quickly. Only the 2nd character would then need masking (assuming that one character is ALWAYS plotted first)