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From: jesup@steinmetz.steinmetz.UUCP (Randell Jesup)
Newsgroups: comp.sys.amiga
Subject: BltMaskBitMapRastPort
Message-ID: <6978@steinmetz.steinmetz.UUCP>
Date: Tue, 11-Aug-87 19:56:44 EDT
Article-I.D.: steinmet.6978
Posted: Tue Aug 11 19:56:44 1987
Date-Received: Thu, 13-Aug-87 06:46:49 EDT
References: <1702@amiga.amiga.UUCP>
Reply-To: jesup@kbsvax.steinmetz.UUCP (Randell Jesup)
Organization: General Electric CRD, Schenectady, NY
Lines: 29
Summary: It's brain-damaged!

I've been doing some 4-bitplane, 640x200 graphics work and wondered why, every
time I updated a portion of the screen with the new 1.2 BltMaskBitMapRastPort,
there was a white flash in the area before the update.  In that resolution,
things are slow enough that it was VERY annoying.
	I thought to myself, "Why would it flash?  I KNOW the blitter can
handle a source, destination, and 1 other channel as inputs, it should be a
one pass operation."  So I worked out the minterm for a blit through a mask,
and Lo!, it was the the cookie cut minterm, $ca.  (D = AC + BNC in reduced
form).
	And I consulted the 1.2 Gamma 2 Infominder AutoDocs (holy book) and
saw, as I remembered, that only 2 minterms were allowed (1 for straight copy,
one for inverted).  I looked up the values for the minterms, and Lo!, they
were $e0 and $20.  
	And the inspiration struck!  The BltMaskBitMapRastPort was implemented
as Rob Pecks ClipBlitTransparent was, by blasting a hole in the destination,
then blitting in the new version (2 blits on every plane)!
	And I am left with the dilemma:  to use the blitter directly, via
OwnBlitter or QBlit, ignoring the layers library, maybe trashing requestors,
or blit the area masked out onto the source, then back to the destination
(SLOW).
	I implore ye, oh Amiga Gurus, is there any way out of this dilemma?
(Like a way to set up the blits the way BltMaskBitMapRastPort does, but
using the cookie cut minterm?)  And will ye fix it at the soonest possible
moment?  Otherwise, for doing screen updates it is useless.

	Your humble servant,
		Randell Jesup
		jesup@steinmetz.uucp (uunet!steinmetz!jesup)
		jesup@ge-crd.arpa