Path: news.uiowa.edu!news.physics.uiowa.edu!math.ohio-state.edu!howland.erols.net!news-peer.gsl.net!news.gsl.net!portc01.blue.aol.com!newstf01.news.aol.com!newsbf02.news.aol.com!not-for-mail
From: rubywand@aol.com (RUBYWAND)
Newsgroups: comp.sys.apple2.programmer
Subject: Re: Looking for IIGS Image Format Info
Date: 15 Oct 1996 01:34:37 -0400
Organization: America Online, Inc. (1-800-827-6364)
Lines: 73
Sender: root@newsbf02.news.aol.com
Message-ID: <53v7pd$41f@newsbf02.news.aol.com>
References: <53slc8$erd@darla.visi.com>
NNTP-Posting-Host: newsbf02.mail.aol.com
X-Newsreader: AOL Offline Reader

In article <53slc8$erd@darla.visi.com>, nathan@visi.com (Nathan Mates)
writes:

>In article <53rv03$o1f@newsbf02.news.aol.com>,
>RUBYWAND <rubywand@aol.com> wrote:
>>     Right; this sounds like the Nibble article describing SuperPac.
>
>   Spelt 'Packbytes'.


     Actually, it really is "SuperPac" (Nibble: January, 1988).
SuperPac is a vertical scan packer-unpacker. The basic format
of a packed SP pic is as follows:

PREFIX (16 bytes):  X-Start, X-End+1, YStart, YEnd+1,
Repeat Byte, Format Byte, Len-lo, Len-hi (length of
PREFIX + PACKED PIC DATA)
The remaining 8 bytes are uncommitted and may be
used to link a pic sequence, music, etc..

The Repeat Byte tells the Unpacker that the next two
bytes contain the Byte to be written followed by a
count. The Repeat Byte is selected during Packing by
first scanning the pic (or partial pic) for lowest-count bytes.

The Format Byte is, at present, either a $D3 ("S") or a
$C4 ("D"). "S" format means the Pic Suffix (Scanline,
"reserved", and Palette info) is appended to the Packed
Pic Data.
"D" format means the Pic Suffix is not appended. "D"
format saves time and disk space since,  if several pics
employ the same Scanline/Palette setup, only the first
pic in the series needs to be "S" format to load in
the Pic Suffix. 

PACKED PIC DATA: This comes from Pic bytes scanned
vertically, top-to-bottom, moving left to right. The region
is defined by XS ,XE, YS, YE. It may be the entire pic or
some rectangular part of the pic. Partial pics are useful for
doing overlays, as in producing animation. (XS, etc. need not
be the same during Unpack. A section packed from one 
region, may be unpacked at some other.)

Non-repeats and runs of fewer than four are encoded 'as is'.
Runs greater than four are encoded as follows:

Repeat Byte, Byte, Count. For example, if the Repeat
Byte is B3, then B3 11 FF says "write $11 255 times".

PIC SUFFIX: This includes Scanline, Reserved, and Palette
bytes. The Pic Suffix is has a length of 768 bytes and is
not packed. Since all Scanline and Palette data is preserved,
SuperPac can pack and unpack any screen with no loss
of colors for pics using multiple palettes.


>>....
>>     As to specifics on packed formats, perhaps Nathan, Tom, or someone
>>else will put up detailed docs on an ftp site. SuperPac, of course, was
>>thoroughly documented in Nibble.
>
>   That'd be Packbytes, and the 4 lines needed to describe it in
>Toolbox Ref #1 (look for it in the Misc Toolset chapter) are more than
>sufficient.
>

     The PackBytes info is on page 14-39. (All this time, I've been
looking for stuff on "Apple Preferred" format.)  Thanks for the reference!




Rubywand