Path: utzoo!mnetor!uunet!cbmvax!steveb
From: steveb@cbmvax.UUCP (Steve Beats)
Newsgroups: comp.sys.amiga
Subject: Re: Info on Blitter Line Drawing
Message-ID: <3131@cbmvax.UUCP>
Date: 12 Jan 88 15:21:55 GMT
References: <2374@cup.portal.com>
Reply-To: steveb@cbmvax.UUCP (Steve Beats)
Organization: Commodore Technology, West Chester, PA
Lines: 21

In article <2374@cup.portal.com> Chad_The-Walrus_Netzer@cup.portal.com writes:
>
>      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).

Yeah, no problem.  Instead of using USEA|USEC|USED in bltcon0 leave off the
USED term.  Set everything else up to draw a line as normal, your minterms
will be NAC+B (~a^c|b I think) which works out to a code of $ca.  Leaving
out the USED term disables the output (though the blitter will still read
the source bitmap from bltcpth and mask it with the line bit in bltadat).
Of course, you will have to do this for every bit plane in your display.
I haven't tried this but I see no reason why it shouldn't work, suck it and
see.  I have some assembler source for line drawing which I can provide if
needed.

	Steve