Difference between revisions of "Riven tBMP resources"

From A look inside The Link @ wiki
Jump to: navigation, search
(these should do until the byte pattern code gets up and running)
 
m (TOC)
Line 1: Line 1:
 +
{{Riven}}
 
This page shows the structure of Riven tBMP resources, which store game bitmaps.
 
This page shows the structure of Riven tBMP resources, which store game bitmaps.
  

Revision as of 03:21, 6 February 2008

Riven
Mohawk Overview
BLST CARD FLST HSPT
MLST NAME PLST RMAP
SFXE SLST tBMP tMOV
tWAV VARS VERS ZIPS
Scripts Variables
External commands

This page shows the structure of Riven tBMP resources, which store game bitmaps.

General tBMP structure

tBMP resources store 8-bit and 24-bit bitmaps, which can be plain or compressed. Everything is in big-endian order. Each resource begins with this structure:

unsigned short bitmap width (pixels)
unsigned short bitmap height (pixels)
unsigned short bytes per row
unsigned char compression flag
unsigned char truecolor flag

If the truecolor flag is 4 then the bitmap is a 24-bit image, and the structure goes on with height rows, each row following this structure:

width*3 unsigned chars pixel values (BGR, BGR, BGR...)
width unsigned chars unknown (zero)

Note that there is only one 24-bit bitmap in the whole game! It's tBMP 24 in b2_data.mhk, and it's a secret image.

If the truecolor flag is not 4 the tBMP is a normal 8-bit bitmap and after the initial fields we find:

unsigned long unknown (seems always 0x030418ff)
256*3 unsigned chars color table (BGR, BGR, BGR...)

If the compression flag is 0, the bitmap is uncompressed: pixel data follows immediately as a simple block of pixels. Each pixel is a byte representing an index in the color table. Rows may be padded with filling bytes to reach the specified number of bytes per row; just discard those extra bytes. Otherwise, if the compression flag is 4 then the bitmap is compressed with a proprietary format (explained below); the compressed data block follows immediately.

Compression details

In compressed tBMP bitmaps, pixels are encoded as a data stream made of variable length commands. Pixels are always decoded in duplets: each command generates at least 2 pixels. The encoding is heavily based on what comes before each command, so even a little decoding bug can cripple the whole image. The commands can appear in any order inside the data stream. The first 4 bytes of the data stream are unknown and can be ignored. Many thanks to Arthur Muller for his precious help in decoding this format. Main commands

They are all 1-byte commands, followed by a variable number of arguments.

Command Action
0x00 End of stream: when reaching it, the decoding is complete. No additional bytes follow. I think some bitmaps don't have this, so just stop when you have decoded enough pixels to fill the image.
0x01 -0x3f Output n pixel duplets, where n is the command value itself. Pixel data comes immediately after the command as 2*n bytes representing direct indices in the 8-bit color table.
0x40-0x7f Repeat last 2 pixels n times, where n = command_value & 0x3F. No additional bytes follow.
0x80-0xbf Repeat last 4 pixels n times, where n = command_value & 0x3F. No additional bytes follow.
0xc0-0xff Begin of a subcommand stream. This is like the main command stream, but contains another set of commands which are somewhat more specific and a bit more complex. This command says that command_value & 0x3F subcommands will follow. It doesn't generate pixels itself.

Subcommands, part 1: arithmetic operations

Subcommands are not simply 1-byte values, but are somewhat mixed with their arguments, so the full byte pattern is reported.

Command Byte pattern Action
0x01-0x0f 0000mmmm Repeat duplet at relative position -m, where m is given in duplets. So if m=1, repeat the last duplet.
0x10 0x10 p Repeat last duplet, but change second pixel to p.
0x11-0x1f 0001mmmm Output the first pixel of last duplet, then pixel at relative position -m. m is given in pixels.
0x20-0x2f 0010xxxx Repeat last duplet, but add x to second pixel.
0x30-0x3f 0011xxxx Repeat last duplet, but subtract x to second pixel.
0x40 0x40 p Repeat last duplet, but change first pixel to p.
0x41-0x4f 0100mmmm Output pixel at relative position -m, then second pixel of last duplet.
0x50 0x50 p1 p2 Output two absolute pixel values, p1 and p2.
0x51-0x57 01010mmm p Output pixel at relative position -m, then absolute pixel value p.
0x59-0x5f 01011mmm p Output absolute pixel value p, then pixel at relative position -m.
0x60-0x6f 0110xxxx p Output absolute pixel value p, then (second pixel of last duplet) + x.
0x70-0x7f 0111xxxx p Output absolute pixel value p, then (second pixel of last duplet) - x.
0x80-0x8f 1000xxxx Repeat last duplet adding x to the first pixel.
0x90-0x9f 1001xxxx p Output (first pixel of last duplet) + x, then absolute pixel value p.
0xa0 0xa0 xxxxyyyy Repeat last duplet, adding x to the first pixel and y to the second.
0xb0 0xb0 xxxxyyyy Repeat last duplet, adding x to the first pixel and subtracting y from the second.
0xc0-0xcf 1100xxxx Repeat last duplet subtracting x from first pixel.
0xd0-0xdf 1101xxxx p Output (first pixel of last duplet) - x, then absolute pixel value p.
0xe0 0xe0 xxxxyyyy Repeat last duplet, subtracting x from first pixel and adding y to second.
0xf0 and 0xff 0xfx xxxxyyyy Repeat last duplet, subtracting x from first pixel and y from second.

Subcommands, part 2: repeat operations

Command Byte pattern Action
various 1x1xxxmm mmmmmmmm
Command n r
0xa4 - 0xa7 2 0
0xa8 - 0xab 2 1
0xac - 0xaf 3 0
0xb4 - 0xb7 3 1
0xb8 - 0xbb 4 0
0xbc - 0xbf 4 1
0xe4 - 0xe7 5 0
0xe8 - 0xeb 5 1
0xec - 0xef 6 0
0xf4 - 0xf7 6 1
0xf8 - 0xfb 7 0

Repeat n duplets from relative position -m (given in pixels, not duplets). If r is 0, another byte follows and the last pixel is set to that value. n and r come from the table on the right.

0xfc 0xfc nnnnnrmm mmmmmmmm (p) Repeat n+2 duplets from relative position -m (given in pixels, not duplets). If r is 0, another byte p follows and the last pixel is set to absolute value p.