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From: toddpw@tybalt.caltech.edu (Todd P. Whitesel)
Newsgroups: comp.sys.apple
Subject: Re: //gs screen resolutions...
Message-ID: <1990Feb9.212016.22527@spectre.ccsf.caltech.edu>
Date: 9 Feb 90 21:20:16 GMT
References: <10078.infoapple.net@pro-generic>
Sender: news@spectre.ccsf.caltech.edu
Organization: California Institute of Technology
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sysop@pro-generic.cts.com (Matthew Montano) writes:

>  I constantly have this problem with people in the store at which I work.
>They brag about how the Amiga has all these 640*400 resolutions with 256
>colors and how awesome the games would be. It takes easily an hour to explain
>how such a high resolution with so many colors is virtually impossible to
>animate at any speed which is worthwhile. The same thing occurs with IBM

First, the stock Amiga can only get 32 colors out of a raw display. Forget 256,
because the current Amiga video is done via DMA, and to get much more than 4
bit color they have to suck bandwidth from the video buffer (this is only a
problem when the 68K is running in the buffer, though. expansion RAM takes
care of it because it is devoted to the CPU much like the fast RAM and standard
RAM in the //gs, only more efficiently designed. (Much of the //gs was so
improperly implemented that there had to be political factors involved.)

640x400 is accomplished on the Amiga by (a) reducing the number of bitplanes,
and (b) interlacing the video.

>screen or less! Most (if not all) Amiga games are in a 320*200 mode in 16
>colors. Some of the newer ones are 640*4X0 resolution still in 16 colors, and
>they sometimes over power the hardware. Do you know how much 640*400*16 takes
>up in memory? How about 256 colors per pixel... forget it.

640x400x16 colors takes up almost 128K of buffer. 256 colors is double that
(256K), and 640x480x256 colors takes a whopping 307200 bytes. (24 bit color?
triple that.)

The only way to handle that much resolution with any acceptable speed is to
have (a) blindingly fast CPU (i.e. Mac //ci) or (b) to use a cheap blitter
with hardware memory moves and logic operations hardwired into it (the Agnus
chip in the Amiga).

Apple needs to develop a simple custom blitter to handle all the QuickDraw
grunge which is the real reason the desktop is so slow. Blitters are always
better because they don't have the instruction stream overhead of a general
purpose processor, and thus do much more per clock, and are cheap to make.
Plus they run in the background, so the CPU just has to load the control
registers, just like the DOC.

>  The higher resolution 640*400 (or whatever) is perfectly suited for desktop
>applications. Anything that uses the desktop would be suited for such a
>resolution. A HyperCard like application would love such a resolution..

>  Games in that higher resolution ESPECIALLY with more than 4 colors would be
>really pushing the machine (any machine).. think AWGS like programs, hypercard
>like applications.. but never games.

Well... many games on the Amiga require the blitter to be as fast as they are.

I am continually amazed at what people have done with the //gs's 65816. The
desktop would be a lot cleaner if Apple would rewrite most of the desktop
routines to use the block move instructions and VBL, so we would get nice
fast and clean looking redraws.

Todd Whitesel
toddpw @ tybalt.caltech.edu