A Description of the
ZPack 1 File Format


Tim Meekins, Zavtra Software
8372 Morris Rd.
Hilliard, OH 43026
(614) 878-6557

January 9, 1991

ZPACK 1 is a file format for storing compressed Super Hi-Res images on
an Apple IIgs. ZPACKĘ1 uses a proprietary algorithm for the actual
compression. A toolset is available from the author for using both the
ZPack algorithm and the ZPACK 1 file format and other additional
formats. The ZPack toolset must be licensed from the author if it is to
be used in a commercial computer program or application.

ZPACK 1 files are stored as binary files and the file name ends with
the suffix ".ZP1".

The following is a description of the actual file format:

ZPackID	3 characters "ZP1" ($5A $50 $31).
ZPackRev	1 byte. Major revision number of ZPack toolset. Currently $01.
ScanLineArray	[0..199] of ZPacked scanlines. Each unpacked scanline is 160 bytes.
PackedSCB	ZPacked SCB. Originally 200 bytes.
PaletteArray	[0..15] of ZPacked palettes. Each unpacked palette is 32 bytes.

The following pseudo-code demonstrates how a ZPACK 1 file is created
using the ZPack algorithm:

	Output "ZP1"
	Output ZPackVersion()
	OldRow <- NULL
	FOR row <- 1 to 200
	ZPack(160,&scanline[row-1],OldRow, Output)
	OldRow <- &scanline[row-1]
	NEXT
	ZPack(200,SCB,NULL,Output)
	OldPal <- NULL
	FOR pal <- 1 to 16
	ZPack(32,&palette[pal-1],OldPal,Output)
	OldPal <- &palette[pal-1]
	NEXT

This pseudo-code is already implemented in the tool function ZP1Pack so
it is not necessary to learn the details and nuances of a ZPack 1 file.
Additional documentation and example source code is available from the
author, Tim Meekins, demonstrating the proper usage of the ZPack
toolset.

See also: Meekins, Tim, "ZPack Reference Manual 2.0", Zavtra Software, 1991.