🚀 go-pugleaf

In article <3074@goanna.cs.rmit.oz.au> phi@goanna.cs.rmit.oz.au (Philip Hingston) writes:
>I need a blit where the source overrides the destination except where the
>source has colour 0, when the destination show through. Is there a blit for
>this or must I make my own? Thanks.		phi

Tom Rokicki will probably provide more info on this subject.

Since the blitter operates as "dest=function_of(dest,source,mask)", you will
have to first calculate the mask which indicates where the color_0 pixels
are located in the source.  For instance:
	mask = all zeros
	for 2 bit-planes at a time do
	  mask = mask OR plane1 OR plane2
	endfor  (mask now has 0 where ever the source is color_0)
	dest = (dest AND NOT mask) or (source AND mask)
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