Riven tBMP resources

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.

Like the uncompressed format, sometimes duplets are generated beyond the edge of the image. Use the bytes per row value to see how many duplets are in each row.

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

Sometimes these repeat commands will try to copy more than what is available when the command is read. In those cases, the command repeats the available segment of data until the number of duplets needed is copied. Or, equivalently, the command starts copying data that it wrote earlier.

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.