OBJ file
OBJ files contain the sprites graphics (equivalent to the C ROMs on cartridge systems). Data is compressed however using a simple RLE compression removing runs with a value of 0x00000000. Once decompressed the format is described here: sprite graphics format.
RLE compression.
- First long word value is the compressed file length (/4-1).
- The system works by checking single long words at a time.
- When a zero value is found it is stored and the next value is checked. A fill of zero is created to match the value read unless it is zero.
Example.
compressed:
0x00000007, 0x11111111, 0x00000000, 0x00000003, 0x22222222, 0x00000000, 0x00000000, 0x33333333, 0x44444444
decompressed:
0x11111111, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x22222222, 0x00000000, 0x33333333, 0x44444444
This system will not compress data very well unless there are large areas of zero data within the decompressed sprite data. This is due to a single zero value run being inflated by 100% (single long word to double long word).
To my current knowledge only Art of Fighting uses the OBJ format.
For reference below is a 68000 code snippet from bios TOP-SP1 that handles decompresses.
C0BC5A 203C 00E0 0000 MOVE.L #0xE00000,D0
C0BC60 D0AD 7EF4 ADD.L (0x7EF4,A5),D0
C0BC64 2240 MOVEA.L D0,A1 <---- Where to decompress data
C0BC66 206D 7EF8 MOVEA.L (0x7EF8,A5),A0
C0BC6A 7000 MOVEQ #0x0,D0
C0BC6C 2E18 MOVE.L (A0)+,D7 <---- Get Length
C0BC6E 6738 BEQ.S *+0x3A [0xC0BCA8]
C0BC70 22D8 MOVE.L (A0)+,(A1)+ <---- Move single long word
C0BC72 6712 BEQ.S *+0x14 [0xC0BC86] <---- Branch if zero.
C0BC74 51CF FFFA DBF D7,*-0x4 [0xC0BC70] <---- check data end
C0BC78 2009 MOVE.L A1,D0
C0BC7A 0480 00E0 0000 SUBI.L #0xE00000,D0
C0BC80 2B40 7EF4 MOVE.L D0,(0x7EF4,A5)
C0BC84 4E75 RTS
C0BC86 2C18 MOVE.L (A0)+,D6 <---- Get next value
C0BC88 51CE 0014 DBF D6,*+0x12 [0xC0BC9E] <---- Decompress if non zero
C0BC8C 51CF FFE2 DBF D7,*-0x1C [0xC0BC70] <---- Check data end
C0BC90 2009 MOVE.L A1,D0
C0BC92 0480 00E0 0000 SUBI.L #0xE00000,D0
C0BC98 2B40 7EF4 MOVE.L D0,(0x7EF4,A5)
C0BC9C 4E75 RTS
C0BC9E 22C0 MOVE.L D0,(A1)+ <---- Recreate zero run
C0BCA0 51CE FFFC DBF D6,*-0x2 [0xC0BC9E] <---- and Loop until complete
C0BCA4 51CF FFCA DBF D7,*-0x34 [0xC0BC70] <---- Check data end
C0BCA8 2009 MOVE.L A1,D0
C0BCAA 0480 00E0 0000 SUBI.L #0xE00000,D0
C0BCB0 2B40 7EF4 MOVE.L D0,(0x7EF4,A5)
C0BCB4 4E75 RTSThis system will not compress data very well unless there are large areas of zero data within the decompressed sprite data. This is due to a single zero value run being inflated by 100% (single long word to double long word).
To my current knowledge only Art of Fighting uses the OBJ format.