Path: utzoo!utgpu!attcan!uunet!lll-winken!ubvax!ames!killer!elg
From: elg@killer.DALLAS.TX.US (Eric Green)
Newsgroups: comp.arch
Subject: Re: Sw vs. Hw BitBlit.
Keywords: BitBlit.
Message-ID: <4965@killer.DALLAS.TX.US>
Date: 29 Jul 88 02:46:49 GMT
References: <399@ma.diab.se> <1313@ucsfcca.ucsf.edu> <61783@sun.uucp>
Organization: The Unix(R) Connection, Dallas, Texas
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In message <61783@sun.uucp>, guy@gorodish.Sun.COM (Guy Harris) says:
>If a BitBlt chip is reasonably cheap, and can do the whole job, it may be worth
>it.  Note that in the cases shown, you got at most a 3.5x speedup (scroll
>screen horizontally).  For vertical scrolling, you got only 1.18x; for randomly
>drawing the letter 'a', you got only 1.23x; and for texturing a random 40x40
>square, you got 1.95x.  How cheap does it have to be for that to be worth it?
>(The "do the whole job" comes from comments made in the paper that a
>half-hearted hardware assist can get in the way, rather than help.)
>

It's interesting to note that the Amiga chipset was originally
designed for "the ultimate video game", which required a) low cost,
and b) the ability to move random irregularly shaped objects with
blazing speed, doing logic operations upon the operands (e.g. one
favorite video game trick is EOR'ing in the moving object into the
background bitmap, then EOR'ing it out when it's ready to be moved,
and EOR it into the new location).    Amazing how well-suited such a
chip is for a low-cost windowing system... well, not-so-amazing,
really, since the chipset designers knew an aweful lot about designing
high speed video systems, while the designers of the Sun probably
didn't have that experience when they were faced with the problem of
speeding up their graphics rendering. Seems like the video game jocks have
something to show us Unix jocks, after all....

Just some meaningless trivia to generate flames... ;-)

     Eric

--
Eric Lee Green    ..!{ames,decwrl,mit-eddie,osu-cis}!killer!elg
          Snail Mail P.O. Box 92191 Lafayette, LA 70509              
       MISFORTUNE, n. The kind of fortune that never misses.