Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!oliveb!amiga!jimm
From: jimm@amiga.UUCP (Jim Mackraz)
Newsgroups: comp.sys.amiga
Subject: Re: multiple rastports for a single bitmap
Message-ID: <1991@amiga.UUCP>
Date: 14 Mar 88 19:04:47 GMT
Reply-To: jimm@amiga.UUCP (Jim Mackraz)
Organization: Commodore-Amiga Inc., 16795 Lark Ave. Suite 106, Los Gatos CA 95030
Lines: 31

--

Well, "you're close, you're real close," to paraphrase the psycho
with the grenade launcher in Apocalypse Now.

You can set up a several "pure" rastports to draw with different
offsets into the self-same raster (bitplanes).  It is, however, done
at the bitmap level.  Keeping the BytesPerRows and Rows fields the
same (well, maybe not Rows), you can vary the Planes[] addresses and
get *something* useful.

Problem is, a Window's rastport has a Layer hanging off of it.  To do
the similar vudu, you need to set up different Layers (which is not
at all easy; perhaps never been done).  There are some parameters
Scroll_X and Scroll_Y which probably apply.

It's getting too hard for me, but feel free to pioneer.

I think it would be lots easier to put a layer between yourself
and graphics that adds a few offsets to each drawing command.
E.g.: MyBltBitMapRastPort( ) and so on.

Maybe if you figure out a layers trick you can talk at the 1989 
Developers' Conference.  ;^)

	jimm

-- 
	Jim Mackraz, I and I Computing	  
	amiga!jimm	BIX:jmackraz
Opinions are my own.  Comments regarding the Amiga operating system, and
all others, are NOT to be taken as Commodore official policy.