Re: [9fans] ati radeon support

[Charles Forsyth <forsyth@caldo.demon.co.uk>]

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that code was indeed quite complicated (it seemed to wander back and
forth between draw, mouse and screen in a way that was probably straightforward
but always left me a little confused for a few passes).

for performance, i think it depends how it's done.  i didn't do the Inferno one, but i did
use it without obvious trouble with Inferno on a 486sx33 processor.  in one of my
own os's i did the software cursor in a process on a 386sx16 and
that was fine too, although that was only 16x16 in bits on a monochrome screen.
neither controlled it with the clock, though, which might have made it smoother.

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From: jmk@plan9.bell-labs.com
To: 9fans@cse.psu.edu
Subject: Re: [9fans] ati radeon support
Date: Fri, 3 Oct 2003 14:28:09 -0400
Message-ID: <92f0483b4252b9cd48e240d6d4122c65@plan9.bell-labs.com>

On Fri Oct  3 13:57:55 EDT 2003, forsyth@vitanuova.com wrote:
> yes, the problem with graphics cards is really the strange card-specific stuff
> needed to put it into a reasonable large, deep linear colour mode.
> if we had only to write code for the hw cursor for each one,
> that would be much less of a problem.  even some of the hardware
> drawing code doesn't look hard to exploit ... once the card is in a sensible mode.
>
> the cursor code always seemed fairly similar, so it might not be too hard
> to have a table of ids just for that if necessary, and certainly card-specific
> code for that is fairly easy to write.  one of the changes i
> was making to the software cursor in inferno is to bring it
> into a common interface with the hardware one
> (allowing for the need to interact a bit with devdraw re. screen access).

The reason the software cursor disappeared form Plan 9 was, by the time
devdraw went in, the cursor and mouse code had accumulated so much cruft
after years of adapting to new graphics models and hardware that it was
a constant source of lockups and crashes. There was an attempt when changing
to devdraw to pare all that back and simplify it. The software cursor
was the cause of many of the problems.

The software cursor is OK for getting started, but I'd hate to use it
in earnest. The flicker when scrolling text was awful and I'm trying to
imagine what it would be like with vnc.