version 3 / 2025-02-04

This is an unofficial attempt at documenting the module music format used in the Czech MS-DOS games Boovie and Bloodie by Future Games.

Not everything has been figured out. The information may be incorrect.

The format is based on S3M, and the feature set is almost identical. The only notable differences are:

song name and sample names are not stored.
OPL instruments are not supported.

Although the format is based on S3M, all modules that come with the games seem to have been 8-channel MOD (FST) files originally, and might have been converted to S3M after they were finished, and finally converted to the game's own format.

The format was reverse-engineered by cs127 with some help from Toppy (gyrominiac).

Remarks

Module format

all numbers are little-endian.
commands are identical to S3M.
pattern data is uncompressed, and stores the data for every pattern channel on every row.
the number of pattern channels is determined by the "number of bytes per row" divided by 5, since each event is 5 bytes long.
if the number of active channels is less than the number of pattern channels, the pattern data for the latter channels is simply ignored, even global commands such as Axx.
all samples are 8-bit mono signed PCM.
the sample map is used to store samples in a different order than their slot indices that are referenced in patterns, or store less samples than there are slots (to avoid storing headers for empty samples). the sample indices in the sample map are 0-based (i.e. 00 means the first sample slot).
sample numbers in patterns don't change the note volume (i.e. note volume is persistent across sample changes). when converting from S3M, for events that have a sample number but no volume, you should add the samples's default note volume as the volume command.

Game engine limitations

all original Scream Tracker 3 commands are implemented, except for Ixy, Rxy, S1x, S2x, S3x, S4x, SAx, and SBx.
initial global volume is ignored.
every pattern is assumed to be 512 events (2560 bytes) long. this makes it practically impossible to have modules with more than 8 channels (40 bytes per row).

File structure

Module

type	content
`u8`	initial tempo
`u8`	initial speed
`u8`	initial global volume
`u8`	number of active channels
`u16`	number of bytes per pattern row
`u16`	number of sample slots
`u8[32]`	initial channel panning ($00..$0F each)
`u8[100]`	order list ($FF = end of song)
`u8`	number of patterns
`pattern[]`	patterns
`u8`	number of stored samples
`u8[]`	mapping of stored samples to slot numbers
`sample[]`	stored samples

Pattern

type	content
`row[64]`	rows

Pattern row

type	content
`event[]`	events

Pattern event

type	content
`u8`	note (0..95 = C-0..B-7, 255 = empty, 254 = cut)
`u8`	sample (0..n = sample 1..n+1, 255 = empty)
`u8`	volume (0..64 = v00..v64, 255 = empty)
`u8`	effect type (0..25 = A..Z, 255 = empty)
`u8`	effect parameter (0..255 = 00..FF, 255 = empty if type is also 255)

Sample

type	content
`u8`	flags (+1 = loop)
`u8`	default note volume
`u16`	-
`u32`	length
`u32`	loop start
`u32`	loop end (inclusive)
`u32`	sample rate
`u32`	-
`s8[]`	data

TODO

are there any notable weird edge cases of sample mapping?

cs127/booviemod.md