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Unless I'm wrong, a drawback of using interleaved bitplanes to do fewer but larger blits is that the mask for the sprite shape gets bigger too.

If you do several blits, one per bitplane, you get to use the same mask data, but when using interleaved data the mask needs the same shape data * number of bitplanes involved.

It's still a pretty small price to pay compared to Atari ST/ZX Spectrum preshifted bitmaps.

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Does that mean you cannot use the Blitter to draw lines and fill area as described in the article?

You'd use a single multi-bitplane interleaved fill-blit if the background surrounding it did not need to be preserved (eg. no mask requirements as per Flow - demos tend to do this for its speed).

I'd imagine Another World creates an off-screen single-bit deep bitmap and uses that as a mask. I sent you an email if you'd like to explore more, however the original programmer probably just remembers what he actually did.

Also note that non-overlapping polygons can be grouped together in both approaches by line-blitting with XOR destination (adjacent polygons share an edge and so the edge is XOR blitted twice); so there are substantial speed-ups to be had.

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