Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!wuarchive!waikato.ac.nz!ldo
From: ldo@waikato.ac.nz (Lawrence D'Oliveiro, Waikato University)
Newsgroups: comp.arch
Subject: Re: Dynamic Display Architecture
Message-ID: <1991Apr18.172428.3490@waikato.ac.nz>
Date: 18 Apr 91 05:24:28 GMT
References: <1991Apr15.200955.3438@waikato.ac.nz> <3340@crdos1.crd.ge.COM> <20670@cbmvax.commodore.com> <1991Apr17.051746.15592@sbcs.sunysb.edu>
Organization: University of Waikato, Hamilton, New Zealand
Lines: 45

Do any of these hardware windowing systems support anything resembling
the Macintosh Palette Manager? This seems to me the only reasonable way
to manage colour-table devices in a multi-tasking, multi-display
environment.

The way it works is that, instead of applications having to manipulate
device colour tables directly, you instead attach a "palette" of requested
colours to each window. The Palette Manager looks at the frontmost window,
looks at the hardware capabilities of the screens it's on, and sets
up the colour hardware as appropriate to optimize the display of that
window. If there are any colour registers left over, it then assigns some
to the next window from the front, and so on.

Note that a window might straddle multiple screens, with different
hardware capabilities: one screen might only support black-and-white,
another might have 8 bits per pixel, and yet another might be a 24-bit
direct-RGB display with no colour table at all. You really don't want the
headache of having to worry about all this, not to mention trying
to arbitrate access to display hardware among multiple applications running
at once. And then have to redo it all when the user changes the screen
mode while your program is running.

There are lots of options to give the application fine control, and
access to special functions. In the simplest case, you can adjust
the tolerance of a palette entry, so that you can tell the system that
you would be satisfied with a less-than-exact colour match. This could
let you share colour registers with other windows on the same screen.

There are even functions specifically to allow you to do colour-table
animation, including animating a previously-generated image (Of course,
these only work on a display *with* a colour table). And you can
specify that certain palette entries are only active at certain
screen depths (or only on black-and-white displays, or only on colour
ones), which lets you hand-tune the display to look the best,
no matter what kind of display hardware you're running on.

Is there any windowing hardware which will support this, or, at least,
not prevent the OS from supporting something like this?

Lawrence D'Oliveiro                       fone: +64-71-562-889
Computer Services Dept                     fax: +64-71-384-066
University of Waikato            electric mail: ldo@waikato.ac.nz
Hamilton, New Zealand    37^ 47' 26" S, 175^ 19' 7" E, GMT+12:00
The rest of this message is printed in that special font they use
for the expiry dates on food packages.