Mega Man Legends 2

This page contains notes for the game Mega Man Legends 2.

Archive files#

.BIN files found on the disc containing various assets. A file will occupy a number of $800-byte pages before the next file in the archive. Leftover space on a page will be zeroes.

File header#

Every file in the archive starts with a $30-byte header. The purpose of the first three words is consistent across all file types.

Offset	Purpose
$00000000	File type
$00000004	Size of file (uncompressed size if compressed file)
$00000008	Number of pages until next file in archive

File type 2: external color data#

A file containing only a header and color data. Some images need to be combined with one of these.

Offset	Purpose
$00000010	Number of colors included (halfword)

Halfwords for every color come after the header.

File type 3: compressed TIM#

Contains a compressed image, optionally including color data (CLUT), before the image in that case.

Offset	Purpose
$00000010	Number of colors included (halfword)
$00000018	Width of image (halfword). Needs to be doubled depending on codec.
$0000001A	Height of image (halfword)
$00000024	Pointer to start of compressed data (halfword). Add $30 to account for the header.

Bitmasks for decompression#

Directly after the header comes a number of 32-bit words where each bit from left to right corresponds to a 16-bit halfword in the compressed stream. 0 denotes a literal halfword to copy as is. 1 means the halfword is a reference backwards. When 32 bits have been consumed, the next mask is read.

Reference halfwords#

The upper 13 bits give an offset in the reference window (ca $2000-byte area) to copy from. The window is at the start of the output stream at first. The lower 3 bits tell how many halfwords, minus 2, to copy from there.

If a reference halfword is $FFFF, however, the position of the reference window is updated to start at what the current output position is when this is encountered.

Checking if full output size has been reached works to determine end of decompression.