Date: Tue, 31 May 1994 11:04:40 -0400 (EDT)
From: Edwin Phillips <flaregun AT strauss DOT udel DOT edu>
Subject: GRX
To: DJGPP mailing list <djgpp AT sun DOT soe DOT clarkson DOT edu>


	I talked to Csaba a while back about adding a "transparent" mode
to GrBitBlt().  This would be useful for making "sprite"-like screen
images, which can be just small rectangular arrays of bytes (256 color
mode).  The trick is, instead of having an image and a mask, you can just
copy all pixels, except background pixels, to the screen.  I originally
wrote a sprite library for TurboC++ using this technique.  I does require
a good deal of overhead to determine which pixels are "transparent", i.e. 
you can't use rep movsw.  Is anyone interested in this?  I have looked at
the source to GRX, but it is all a wash.  He has done such a great job
supporting all of the possible modes (1, 4, 8, 16bit (24bit?)), that it's
really difficult to see how it works.  This would only be usable for an
8bit mode (mayyybbee 16bit).  I don't know... you can't really do any kind
of animation (FAST, mind you) without some way of doing this simple kind
of image copy.  I admit, there's probably a way to do this with palette
tricks, and XOR, etc., but nothing as straightforward (and possibly as 
fast) as such a technique.

	Ed

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/* Ed Phillips  flaregun AT strauss DOT udel DOT edu      University of Delaware       */
/* Jr Systems Programmer  (302) 831-6082   CNS/Network and Systems Services */
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