Puzzle image (X11)

Some distributions of X-Windows include a program named "puzzle", which is an implementation of the "15 puzzle" sliding tile game. It was written by Don Bennett of HP Labs.

Using the " " option, a custom bitmap image may be used on the tiles. This article is about the format of the file containing that custom image. It has been given various names such as X11 puzzle file or Unix Puzzle 8-bit Bitmap.

Format
A puzzle image uses a simple uncompressed 8-bit paletted format. There is a 5-byte header, then the palette, then the pixels.

Specifications
The format is described in a comment in the picture.c file from the source code.
 * ftp://ftp.x.org/pub/unsupported/programs/puzzle/picture.c

Software

 * Netpbm: ppmtopuzz (write only)
 * XnView (apparently requires the file extension to be ".pzl")
 * puzzle source code and man page

Sample files

 * mandrill.cm