Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!gem.mps.ohio-state.edu!tut.cis.ohio-state.edu!ucbvax!ucdavis!iris!rogers
From: rogers@iris.ucdavis.edu (Brewski Rogers)
Newsgroups: comp.sys.amiga
Subject: Re: a "mirror image" blit
Message-ID: <5629@ucdavis.ucdavis.edu>
Date: 15 Oct 89 09:16:58 GMT
References: <1647@nigel.udel.EDU>
Sender: uucp@ucdavis.ucdavis.edu
Reply-To: rogers@iris.ucdavis.edu (Brewski Rogers)
Organization: U.C. Davis - Department of Cows and Computer Science
Lines: 24

In article <1647@nigel.udel.EDU> A_HINDS%HVRFORD.BITNET@cornellc.cit.cornell.edu writes:
>
>again.  What I need to do is take source bitmap, and blit its mirror image
>into the destination bitmap.  Now I know this can be done with low-level
>bliter calls, but I can't seem to figure out quite how to do it.
>        For example, if the area to be blitted is a 10x10 square, I want
>what was (0,0) in the source to become (0,9) in the destination, etc.
>        Any help would be greately appreciated.  I thank you in advance.

What you want do is screw with the modulo's for the blitter rectangles.
Set up the source rectangle pointer to point to the last line of the rectangle,
and set the modulo to some negative value, such that it will get you
to the beginning of line 9 from the end of line 10. Set up the destination
bitmap normally - set the pointer to the beginning of the rectangle,
and use a modulo such that it will get you to the begginning of line 2
from the end of line 1...

Hope this helps...

------------------------------------------------------          Quantum _\/_
2727 Eel                   Bruce (6502 RULES!) Rogers        |\  Duck  ( 0 0)
Davis, Ca 95616            Quantum Duck Software,           |\ \______/ / \\\
916-756-2684               rogers@iris.ucdavis.edu         |\ <  <     |   \/
"It's better to be the real thing than the right thing."     \________/  Quark!