If you are still using the old URL (datacrystal.romhacking.net), please update your bookmarks! The old URL may stop working soon.
The current URL is datacrystal.tcrf.net.
The current URL is datacrystal.tcrf.net.
Sega Ages 2500 Series Vol. 17: Phantasy Star generation:2/Notes
Jump to navigation
Jump to search
Compression
CUE found out the coding algorithm. It's a Lempel-Ziv related one, called Lempel-Ziv Renau.
Structure of files :
- Bytes $0000 to $000a : header
- 2 bytes : signature, always "CM"
- 4 bytes: decoded data length, low endian
- 4 bytes: encoded data length, low endian
- From $000a : ENCODED_DATA
- Then FLAGS. Flags are read bit per bit :
- if bit = 0, then put one byte from ENCODED_DATA and put into DECODED_STREAM
- if bit = 1, then the corresponding half-word in ENCODED_DATA is of the form lllloooooooooooo, where l = length and o = offset. Copy then 'length + 3' bytes from DECODED_STREAM[current_position - offset + 1] to DECODED_STREAM[curent_position].
- Fill the file with $00, up to have a file size dividible by $800.
Files specifications
Graphics files (SGGG)
They are just 256 colors palette indexed bitmap files.
- bytes $0 to $3 : 'SGGG' (identifier)
- bytes $4 to $7 : always 1, usage unknown
- bytes $8 to $9 : width (Little Endian)
- bytes $a to $b : height (LE)
- bytes $c to $f : unknown
- bytes $10 to $410 : palette. Each color is 32b RGBA. Alpha max seems to be $80 (and most colors are alpha max). Colors are stored in a weird way though :
- colors $0 to $7
- colors $10 to $17
- colors $8 to $f
- colors $18 to 1f
- and so on...
- from bytes $410 : bitmap. The picture seems cut in 512×512 blocks in scan order, each of which described row per row, from top to bottom.
For example, a 640×448 bitmap is cut in 2 rects, one with pixels (0 - 511, 0 - 447) and the other (512 - 639, 0 - 447). No bitmap actually need more than 2 rects.
Font file
The font file is file 0002 in MAPDATA.DAT archive. It's a SGGG file (see above) with the following characteristics :
- its size is 512×512
- its palette contains 64 times the 4 same colors : $FFFFFF00, $FFFFFF3A, $FFFFFF5F, $FFFFFF7F. They are all white colors, with varying alpha, for antialiasing purposes when drawing the character
- the bitmap file is actually made of 4 512×512 layers ; each byte in the bitmap part of the SGGG codes 4 pixels, one in each layer :
- bits 0-1 code a 4 colour pixel in layer 0
- bits 2-3 code a 4 colour pixel in layer 1
- bits 4-5 code a 4 colour pixel in layer 2
- bits 6-7 code a 4 colour pixel in layer 3
We can thus obtain those 4 characters sheets :
(todo : insert them)