Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!mailrus!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.atari.st
Subject: Re: Atari's blitter vs. the Mac RISC graphics unit
Message-ID: <10274@cbmvax.commodore.com>
Date: 20 Mar 90 20:28:03 GMT
References: <900319.21333002.006066@SFA.CP6>
Reply-To: daveh@cbmvax (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 54

In article <900319.21333002.006066@SFA.CP6> Z4648252@SFAUSTIN.BITNET (Z4648252) writes:
>Hello all,

>    This is not a direct quote since I'm doing this from memory but the
>March 19th Dallas Morning News announced that Apple announced a RISC
>graphics chip ...
>    The ballyhoo was so intense in the article that the reader would
>really think that this was indeed a 'first'.

It's almost a first in the Macintosh world.  One company's been making a
board based on the VLSI Logic ARM chip, but from what I've read about it,
it's mainly used as a vectorizing engine for CAD programs, not an actual
QuickDraw interpreter. 

>    Now I'm just a dumb 'Joe End User' but what about the blitter chips
>for the Atari ST and Commodore Amiga?  The article also continued with
>phraseology similar to that of the ST and Amiga in that it said that the
>main CPU could now get on with traffic managing tasks rather than the
>actual graphics management.  Still sounds like a blitter to me.  If this
>is indeed a first then WHAT ABOUT the ST and Amiga chips?  I mean, seriously!!?

While what Apple's doing goes a step further than the Amiga's blitter, it's
still far from a first -- Workstations have been doing this kind of thing
for years.  Even PCs have various TI 340 based graphic boards which work in
a similar fashion.  The basic idea here is that the graphic boards
understand a graphics language at a reasonably high level.  The language
could be TIGA, QuickDraw, Display Postscript; the language details aren't
all that important. 

A Blitter, even a clever one like the Amiga's, only works at a pretty low
level.  When you make a function call in your graphics kernel, for
instance, a generic DrawBox() call, the CPU starts up, probably calculates
any clipping necessary, and generates several blitter calls.  Blitter calls
generally move 2 (Atari) or 3 (Amiga) sources, with 16 (Atari) or 256
(Amiga) possible operations, then deposit a result at a destination.  The
Amiga's blitter also does hardware line drawing.  But all of these are
low-level commands.  On a CPU supported graphics board, the graphics kernel
would only have to translate the OS-supported DrawBox() command into the
graphics language supported DrawBox() command.  If the OS and the graphics
engine support the same language, the only work the main CPU does is to
send that command to the graphics engine, possible Wait()ing before going
on (which lets other tasks use the CPU when you're multitasking). 

So, if nothing else, this new Apple card is their first attempt at building
a QuickDraw engine.  Personally, I'm surprised it's taken this long, and
that it's so expensive (around $2,000 as I recall). 

>Larry Rymal:  |East Texas Atari 68NNNers| <Z4648252@SFAUSTIN.BITNET>


-- 
Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests"
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                    Too much of everything is just enough