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From: wogg0743@uxa.cso.uiuc.edu (William Shakespeare)
Newsgroups: comp.sys.apple2
Subject: supporting better graphics on the gs
Message-ID: <1991Apr20.070832.24635@ux1.cso.uiuc.edu>
Date: 20 Apr 91 07:08:32 GMT
Sender: usenet@ux1.cso.uiuc.edu (News)
Organization: University of Illinois at Urbana
Lines: 38

Actually, it would be easier to support larger bitmaps than one would at
first imagine.  Actually, I should say better resolution on a large bitmap.
If one were to put a large video buffer in, for instance, bank $E2, filling
the entire bank (ie., the buffer is twice normal SHR size), and assuming
the hardware to support the buffer existed, the ROM graphics routines could
be used to draw to it, with some minor complications.

Here's how:

The ROMs support 4 or 16 color images (2 or 4 bit planes) and when not
drawing to the normal SHR screen can handle any screen width, as long as
it involves a multiple of 8 bytes (160 bytes/line normally for SHR).  This
feature is to support off-screen bitmaps, but code be used to support a
third party graphics card instead, provided that it used either 2 or 4
bit planes.  I assume that there is a practical limitation of 64k for
such a buffer, but it would still allow QD to support modes like

	o  640x200x16 colors
	o  320x400x16 colors
	o  640x400x4 colors

Obviously, someone would have to produce the hardware to support such a
beast, but one should not think that QD would hinder the production of
higher resolution graphics on the GS, though it would limit available
colors (QD only will understand 16).

There is a hitch involved with toolset which expect the screen to be in
specific place (didn't someone says something about the menu manager?)
But these things could most likely be worked around.

Anyway, just something for you hardware hackers to consider the next time
you're throwing together a graphics board.

--
William ("Shakespeare") Gulstad          /  So where are the C.S. babes?
wogg0743@uxa.cso.uiuc.edu                /  Joni Mitchell for President!
I vote, so I can complain!               /  Did you vote?  Then don't complain!
Republican is the opposite of democracy! /  Tune in, drop out, log on.