NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/comp/sys/amiga/programm/17979

Internet Message Format | 1992-12-31 | 1.9 KB

Path: sparky!uunet!spool.mu.edu!umn.edu!csus.edu!netcom.com!netcomsv!terapin!paulk
From: [e-mail] (Paul Kienitz)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Chunky Pixels vs. Bitplanes (was: Chunky Chip Set...)
References: <[e-mail]>
Message-ID: <[e-mail]>
Date: 30 Dec 92 22:22:57 PST
Organization: BBS
Lines: 28

> Chunky _needs_ to write transparent pixels and _needs_ to care
> about alignment _if_ you do memory access larger than a pixel. You
> either have to use _8bit_ accesses or use the complete buswidth
> with the same constraints as in bitplanes.

Whoa!  Somebody finally pointed out the ugly secret hiding in there
which never seemed to occur to anybody ......

Using chunky display memory with a word length longer than the chunk,
*IS* in some ways a planar display and has the same disadvantages.
One can only get the full advantage of chunky display if you either
access your (for example) 32 bit memory with 8 bit reads and writes,
which could be a significant loss compared to plane-oriented hardware
that always uses whole words, or use a number of bits per pixel equal
to the full width of your memory, which if more than 8 bits is
presumably going to be true-color, which becomes rather awkward due
to the lack of modern CPUs with a wordlength which is a multiple of
three bits ... or then you start having the word value for each pixel
divided into separate bitfields (masks, dual playfields, etc) which means
that in order to work on the actual picture you now have to, in a sense,
do the reverse of what planar systems have to do to access individual
pixels: you have to separate your chunks into layers in order to tease
out the different numbers.

So: chunky is way better than planar with no disadvantages, if you are
building a display for an 8088 system, or if you are an ant or red-green
colorblind or otherwise have a power-of-two number of primary colors
in your eyeball.