BTB (Binary Texture Blob) format

BTB is a GCR-friendly alternative to TPL. A BTB file contains a single texture data and its metadata (size, color format, mipmap settings) but using GCR as container instead of having its own.

The texture data is swizzled and tiled according to the color format in order to be uploaded to Gamecube with zero processing by the game code.

Limits

Field	Limit
Max texture size	65536 x 65536
Max color depth	8 bpc (using RGBA8)

Color formats

Refer to this page for description and specifications for all the color formats

File format

Offset	Name	Data type	Length (bytes)
0x0	Header	BTB header	14
0x20	Texture data	texture data	?
?	Palette data	palette data (optional)	?

Header format

Offset	Name	Data type	Length (bytes)
0x0	Texture width	uint16	2
0x2	Texture height	uint16	2
0x4	Color format	uint8	1
0x5	Mipmaps	byte	1
0x6	Wrap + Filters	byte	1
0x8	Texture data offset	uint32	4
0xA	Texture palette offset (optional)	uint32	4

Color format

ID	Format name
0x0	I4
0x1	I8
0x2	IA4
0x3	IA8
0x4	RGB565
0x5	RGB5A3
0x6	RGBA8
0x7	A8
0x8	CI4
0x9	CI8
0xA	CI14
0xE	CMPR (DXT1)

Wrap + Filters

Bit(s)	Field
0x0 - 0x2	S Wrap
0x3 - 0x5	T Wrap
0x6	Texture filter
0x7	Mipmap filter

Valid values for wrapping modes:

Value	Wrap mode
0x0	Clamp
0x1	Repeat
0x2	Mirror

Valid values for filters:

Value	Wrap mode
0x0	Near
0x1	Linear

Mipmaps

Part	Field	Values
Upper 4 bits	Minimum LOD level	0 to 10 (inclusive)
Lower 4 bits	Maximum LOD level	0 to 10 (inclusive)

Setting mipmaps at 0 will disable mipmapping