Path: utzoo!attcan!uunet!cbmvax!jesup
From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Using CPU instead of Blitter for speed
Message-ID: <12374@cbmvax.commodore.com>
Date: 7 Jun 90 00:27:25 GMT
References: <2888@crash.cts.com> <1032@mpirbn.UUCP> <2984@crash.cts.com> <1990Jun3.164446.12193@ameristar> <1990Jun4.134811.12142@watdragon.waterloo.edu> <30974@ut-emx.UUCP> <136730@sun.Eng.Sun.COM>
Reply-To: jesup@cbmvax (Randell Jesup)
Distribution: comp
Organization: Commodore, West Chester, PA
Lines: 25

In article <136730@sun.Eng.Sun.COM> cmcmanis@stpeter.Eng.Sun.COM (Chuck McManis) writes:
>In article <30974@ut-emx.UUCP> (Jonathan Abbey) writes:
>>I'd like some hard data on the blitter vs. the CPU for polygon rendering..
>>I've heard people here assert that the CPU is faster, even on a 68000.
>
>The definitive answer to this was given by Jeremy Sans (wrote StarGlider)
>at the S.F. DevCon last year. His assesment was that the blitter and the
>CPU were about equal. Where they varied was in the effort it took to set
>up the "blit" versus the speed at which the blit was accomplished. The 
>blitter is faster than the 68000 once it gets going but the 68000 could
>set up for the next blit a lot faster than the blitter could. 68020 and
>above processors won on both counts, mostly because of the instruction
>cache/clock speed issues.

	There are some other caveats as well.  The polygons he was dealing
with are filled with a solid color (no patterning), and are regular in
certain ways, in particular there can only be two edge-crossings on any given
horizontal line through it.  That's far harder (and more expensive) to
check than the amount of time saved, perhaps even on an '030 (then again,
the '020 and '030 are pretty fast, and have better bit-field instructions).

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.cbm.commodore.com  BIX: rjesup  
Common phrase heard at Amiga Devcon '89: "It's in there!"