>> Notice how Ruy's top hair for 0x69/0x6A was placed at 0x6F/0x9F in order to not disturb the layout. Why the hair of the top left pose is offsetted is unknown. Could it be that GFX ROM address 0x0000 could not be used? Analyzing other games also showed that tile 0x0000 was never used.
My guess is that it was easier to encode and use a blank tile than to specify those strange shapes where sprites are non-rectangular. Just tell the hardware the size in tiles and then offer a set of tiles that includes blanks. This could be confirmed or refuted once they find the area in ROM that specifies how to put the tiles together to form a sprite.
It sounds like a complete sprite had to be entirely on one page, so there must be a list of tile numbers to compose a sprite and they would be 1 byte each. since they know the tile layout for some of the poses, they should be able to write down that sequence of bytes and look for it in the ROM, then check if there are zero tiles in there. Or just check the MAME source code since that level of detail was probably all figured out a long time ago for that project :-)
My guess is that it was easier to encode and use a blank tile than to specify those strange shapes where sprites are non-rectangular. Just tell the hardware the size in tiles and then offer a set of tiles that includes blanks. This could be confirmed or refuted once they find the area in ROM that specifies how to put the tiles together to form a sprite.
It sounds like a complete sprite had to be entirely on one page, so there must be a list of tile numbers to compose a sprite and they would be 1 byte each. since they know the tile layout for some of the poses, they should be able to write down that sequence of bytes and look for it in the ROM, then check if there are zero tiles in there. Or just check the MAME source code since that level of detail was probably all figured out a long time ago for that project :-)