TXTR (Metroid Prime)

TXTR is, as the name suggests, the Retro Studios texture format. It's identical from Metroid Prime all the way up to Donkey Kong Country Returns.

Structure

TXTR files contain a very short 12-byte header, followed by the image data.

Header

Offset	Size	Description
0x0	4	Image format. Possible values range from 0x0 to 0xA; see below for more details.
0x4	2	Width
0x6	2	Height
0x8	4	Mipmap count

Image Formats

There are 11 different image formats; these are built directly into GX, so they remain the same across all GameCube and Wii games. Rather than storing pixels in a linear left-to-right order, GX textures encode pixels in large blocks. The size of the block varies depending on the image format.

For example, suppose you have a format that stores 4x4 blocks. Pixels 1-4 of the image will make up the first row of the first block; pixels 5-8 will make up the second row; 9-12 will make up the third row; 13-16 will make up the fourth row, completing the block; and the 17-20 will begin the first row of the second block, appearing directly to the right of the first row of the first block.

ID	Name	Bits per pixel	Block size	Description
0x0	I4	4	8x8	4-bit greyscale intensity values. Two pixels per byte.
0x1	I8	8	8x4	8-bit greyscale intensity values.
0x2	IA4	8	8x4	4-bit greyscale intensity values with an additional 4-bit alpha channel.
0x3	IA8	16	4x4	8-bit greyscale intensity values with an additional 8-bit alpha channel.
0x4	C4	4	8x8	4-bit palette indices.
0x5	C8	8	8x4	8-bit palette indices.
0x6	C14x2	16	4x4	Another palette format. Not used by any official textures.
0x7	RGB565	16	4x4	16-bit colors without alpha.
0x8	RGB5A3	16	4x4	16-bit colors with alpha.
0x9	RGBA8	32	4x4	Uncompressed 32-bit colors with alpha.
0xA	CMPR	4	8x8	DXT1-compressed textures.

External links

• Custom Mario Kart Wiiki: More detailed information on each format, and how to decode them.