Path: utzoo!mnetor!uunet!portal!cup.portal.com!Chad_The-Walrus_Netzer
From: Chad_The-Walrus_Netzer@cup.portal.com
Newsgroups: comp.sys.amiga
Subject: Info on Blitter Line Drawing
Message-ID: <2374@cup.portal.com>
Date: 11 Jan 88 07:56:16 GMT
Organization: The Portal System (TM)
Lines: 27
XPortal-User-Id: 1.1001.2959



      I need some information about blitter line drawing (get out your
Hardware Manual's).  Basically, I'm writing a program where I want to
use a bitmap/buffer as a mask to use in some collision detection.  I
want to know if the blitter (in line drawing mode) can somehow be made
to draw a line in a bitmap, without actually affecting that bitmap (I
just want to read the BZERO bit in DMACONR, to check if the line would
draw into an area that has already been writen to).
       In other words, can I draw a non damaging line into the bitmap,
and still check to see if that line would cross any area with a pixel
set?
	In particular, I would like to know if how the SET/CLR bit in
DMACONR operates.  If I set it, will a line be generated by drawing
zeros instead of ones?  I've done some preliminary tests after slightly
modifying Tom Rokiki's "Blitlab" program, and it didn't produce any
favorable results.
	Also, I want to know exactly what sets the BZERO bit in DMACONR
when in line mode.  Since the blitter's line drawer operates on blocks
of memory, will this bit be set if there are ones in ANY area that the
blitter operated on, or just on the actual line that was drawn.
	The sooner you answer, the sooner I can get my program into the
public domain (I'm working on an Amiga version of the game "Qix").  If I
need to be more descriptive or specific, let me know!   Thanx.


          Chad Netzer
          "If I weren't crazy, I'd just go nuts!"