Path: utzoo!attcan!uunet!wuarchive!udel!princeton!phoenix!pfalstad
From: pfalstad@phoenix.Princeton.EDU (Paul John Falstad)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Blit Wanted
Message-ID: <16816@phoenix.Princeton.EDU>
Date: 29 May 90 02:31:16 GMT
References: <3074@goanna.cs.rmit.oz.au>
Reply-To: pfalstad@phoenix.Princeton.EDU (Paul John Falstad)
Distribution: comp
Organization: Princeton University, NJ
Lines: 22

In article <3074@goanna.cs.rmit.oz.au> you write:
>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

In order to do this, you have to make a mask for the source.  Allocate
one bitplane the size of the source, clear it, and blit all the
bitplanes of the source onto it separately using a D=A+B minterm (0xFC), where
A = the source bitplane, B = D = the mask.  This is assuming your source is
more than one bitplane, of course.  Then, you can do what you want with
a cookie cut, D = AB + nAC (0xCA), where A is the mask, B is the source,
and C = D = the destination.

Or you could just use a bob.  :-)  Though I've had problems with those.
They also require you to make a mask.  Accessing the blitter directly is
more fun anyway.

-- 
Paul Falstad  PLINK:Hypnos GEnie:P.FALSTAD net:pfalstad@phoenix.princeton.edu
Disclaimer: My opinions, which belong to me and which I own, are mine.
-Anne Elk (not AN elk!)  The sun never set on the British empire because
the British empire was in the East and the sun sets in the West.