Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!uoft02.utoledo.edu!desire!arc
From: arc@desire.wright.edu
Newsgroups: comp.sys.atari.st
Subject: Re: Pictures on the ST (Amiga's RULES)
Message-ID: <725.268f2179@desire.wright.edu>
Date: 2 Jul 90 15:27:04 GMT
References: <4b28c24a.20b6d@apollo.HP.COM> <196@next.com> <672.26899914@desire.wright.edu> <1990Jul2.071658.16558@math.lsa.umich.edu>
Lines: 70

In article <1990Jul2.071658.16558@math.lsa.umich.edu>, hyc@math.lsa.umich.edu (Howard Chu) writes:
> Well, just to add more deadweight to the dying discussion... I've just
> finished porting Fractint 12 from MSDOS to the ST, and along the way I
> added some "new" video modes as well. I added 4-color grayscale to the
> monochrome resolution, and made the medium resolution 16 colors, and
> the low resolution has a palette of 256 colors. From my calculations,
> the available palette is 512 * 511 / 2 = 130816 distinct colors. The
> 4 color grayscale is nothing wonderful to look at. Downright ugly, to
> be honest, but it would look good on a monitor with high-persistence
> phosphor. The low resolution mode looks pretty slick, though. Most of these
> fractals look really gorgeous with 256 colors.
> 
> The trick is pretty obvious, it seems. Just use two screens, and flip the
> physical page on every vertical blank. This effectively doubles the number
> of bits per pixel, and as expected, squares the number of colors that can
> be displayed at once on screen. It also introduces an incredibly annoying
> flicker... But hey, Amigans settle for a megapixel display that updates at
> 15 hertz, 30 hertz is a lot better. Sending 4 complete screens at 15 hertz
> on the ST would give, what ... 64K displayable colors out of, oh... 36 bits
> worth of palette. Not that it'd be incredibly worthwhile.... You'd really
> need the same kind of monitor that the Amigans use - an intelligent one
> that assembles the video frames in an internal buffer.
> 
> Going to monochrome is a slightly different story. If you just use two screens
> and flip back and forth between them, you'll get dark, half-light, and light.
> To get 4 distinct levels of grayscale, or to make the significant bits really
> significant, you have to display them onscreen for a longer period of time.
> But that's pretty easy too... So, the 70 hertz monochrome video is split up
> into a low-significance image sent for one-third of the time, or 23.3 hertz,
> and the high-significance image is sent at 47 hertz. The flicker here is
> really really noticable. Anything slower than 30 hertz will be, of course.
> Turning the brightness down or getting a monitor with high-persistence
> phosphor would cure that problem....
> 
> Ok, I guess I've rambled long enough. I've had a lot of fun getting this code
> working, and I personally think the doubled video modes are kinda neat, even
> if the monochrome flicker is as obnoxious as a fluorescent light...
> 
> Now... If you're really really crazed, you can do vertical blank image switching
> *and* horizontal scan palette switching at the same time. I don't think it's
> really practical for general purpose drawing, or for drawing fractals either,
> for that matter. Limiting color selections on a per-scanline basis just seems
> like too much hassle to deal with. But if you wanted to try it, you could
> draw yourself... 256 * 3 swaps per line * 200 lines = 153600 colors per
> screen. I guess that's a bit excessive, given only 130K colors in the palette.
> 
> SO.... I hope this discussion is really, truly dead now, so we can get to
> more interesting things. Meanwhile I'll be submitting fractint for posting
> Real Soon Now. (But sometimes, ya gotta wonder. Why are you spending all
> these cycles drawing these silly pictures???)
> --
>   -- Howard Chu @ University of Michigan
>   ... the glass is always greener on the side ...

Hey, bud, our screens (640x200, 320x200, etc.) update at 60 frames per second. 
ONLY our interlace mode updates at 30 frames per sec.  DON'T even start!!!

 ALso, we have a blitter and many co-proc's and the ONLY "co-processor" YOU
have is a DMA controller, BIG DEAL!  Later

 
 
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