megazeux/mzm.txt

MZM file format: MZX image

This file format is a simple format that describes graphically a 
 rectangular area.
 
b = byte (8bit)
w = word (16bit)
d = dword (32bit)
sN = string of N size (ie N bytes)

header:

pos  size  description
0     s4    "MZMX" tag
4     b     width
5     b     height
6
.           reserved
f           

data:

The data is composed of w * h (width * height) blocks, where each
 block is 6 bytes and contains the following:

pos  size  description
0     b      ID (5 for overlay)
1     b      param (char for overlay)
2     b      color
3     b      under ID (0 for overlay)
4     b      under param (0 for overlay)
5     b      under color (0 for overlay)