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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.micro
Subject: Re: What is \"bitblt\" ?
Message-ID: <6264@utzoo.UUCP>
Date: Fri, 3-Jan-86 17:23:19 EST
Article-I.D.: utzoo.6264
Posted: Fri Jan  3 17:23:19 1986
Date-Received: Fri, 3-Jan-86 17:23:19 EST
References: <976@brl-tgr.ARPA>, <956@terak.UUCP>
Organization: U of Toronto Zoology
Lines: 63

> Bitblt is pretty much restricted to Macintosh-class displays; monochrome
> with a resolution of 640x400 or so. ... At higher resolutions the amount of
> data to be processed becomes overwhelming, even with special-purpose hardware
> performing the operation.  And the amount of memory needed to hold the
> various operands also grows...

Rubbish, it works just fine at 800x1024 and 1024x1280.  And I've seen it
work nicely at something like 1700x2000 (with considerable hardware help),
although it's hard to buy displays with that kind of resolution.  Yes, the
memory needs and processing-bandwidth requirements grow, but not beyond
the realm of practicality.  The Blit does bitblt very quickly indeed at
800x1024 with *no* hardware assist of any kind (its software is, uh, well
optimized!).

> The AND|OR|XOR|NOT operators don't have any particularly obvious meaning
> in color... [and color greatly increases memory needs]...

This is true; bitblt isn't the answer to the prayers of the color display.
But then, name something that does better!

> ...if you have special-purpose bitblt hardware in order to get around the
> speed problems, you have to use non-virtual memory to hold the images...

Does not follow.  There's no reason why bitblt hardware can't use virtual
memory the same way the cpu hardware does, although it adds cost and
complexity.

> Opinion:  bitblt is an endangered species.  The popularity of the bitblt
> concept was because it was such a simple and powerful approach to the
> problems of manipulating bit-images.  In color systems bitblt is neither
> simple nor powerful; it has all the qualities of a ghastly kludge.  With
> very few monochrome-only graphics systems being designed these days,
> bitblt's days are numbered unless someone can come up with an extension
> which will handle color as elegantly as bitblt handled black-and-white.

Nonsense.  This is like saying that monochrome books are an endangered
species:  the color ones get all the hype, but monochrome still does most
of the work.  For about the same reason, too:  adding color while retaining
resolution and clarity greatly increases cost, and the extra expense is
justified only for certain specialized situations.

Even in the microcomputer world, which is haunted by the ghosts of the
TV-as-monitor aberration and the horrendously poor resolution of the early
designs, nobody in his right mind voluntarily edits text on a color monitor.
Fortunately, machines like the Mac and 520ST are finally bringing decent
monochrome into the micro world, although they could do with more resolution.

Even in the workstation world, color is not taking over.  It's increasingly
necessary as an *option* for people like VLSI designers and mechanical
engineers, but monochrome still wins decisively on price when color is not
an obvious necessity.  Bitblt will continue to dominate the monochrome world,
which it is eminently well-suited to, while color graphics will continue to
be a hodge-podge of kludges, simplistic fudges, and warmed-over vector stuff.
(I am speaking of color graphics as opposed to color imaging, the distinction
being that color imaging uses at least 8 bits/pixel and preferably 24 or more
to give realistic rendering of pictures, while color graphics uses a few
bits per pixel in hopes of being useful somehow.)  When I asked Rob Pike about
color Blits a few years ago, he commented (roughly) "I don't think we know
how to use small amounts of color or gray-scale cost-effectively; the money
and chips are better spent on more space for monochrome".  Still true.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry