GTX\GSH (File Format)

GTX and GSH files are used in various Wii U games, including Mario Kart 8. GSH stands for GX2 SHader and GTX stands for GX2 TeXture.

Header

Every GTX/GSH file begins with an 0x20 byte Gfx2 header.

Offset	Size	Description
0x00	4	"Gfx2" File identifier, ASCII string.
0x04	4	Size of header in bytes. Must be the real size (0x20), or header (and hence file) is unreadable.
0x08	4	Major version number. Must be 0x07, or header is unreadable.
0x0C	4	Minor version number. Must be 0x01.
0x10	4	GPU version for which this file is designed for.
0x14	4	Align mode.
0x18	4	Reserved, Always 0x00.
0x1C	4	Reserved, Always 0x00.
0x20	End of Gfx2 header.

Data Blocks

After the header comes some data blocks, data blocks contain a 0x20 byte BLK{ block header followed by data specified by the block type.

Block Header

Offset	Size	Description
0x00	4	"BLK{" Header of the block, ASCII string.
0x04	4	Size of block header in bytes.
0x08	4	Major version number. Must be 0x01 or header is unreadable.
0x0C	4	Minor version number. Must be 0x00.
0x10	4	Block type, it determines the type of the following data.
0x14	4	Size of the following data. In bytes, always 0x9C if the block type is 0x0B.
0x18	4	A unique identifier for this block, allowing it to be referenced by other blocks
0x1C	4	An incrementing index for each instance of a given type.

Block types

Type	Description
0x00	Not actually a valid Block type.
0x01	Follows this block header the end of the file.
0x02	Follows this block header padding. (Used to align following data)
0x03	Follows this block header Vertex shader header.
0x05	Follows this block header Vertex shader program.
0x06	Follows this block header Pixel shader header.
0x07	Follows this block header Pixel shader program.
0x08	Follows this block header Geometry shader header.
0x09	Follows this block header Geometry shader program.
0x0A	Same as 0x09? (Duplicate?)
0x0B	Follows this block header the Image header.
0x0C	Follows this block header the swizzled image data.
0x0D	Follows this block header the swizzled mipmaps data.
0x0E	Follows this block header Compute shader header.
0x0F	Follows this block header Compute shader program.
0x10	Treated like a 0x02 block, users can do what they want with this block.

Image info

The image info directly follows the block header that has a block type 0x0B, and should exactly have a size of 0x9C:

Offset	Size	Description
0x00	4	Dimension. Indicates the "shape" of a given surface or texture (see line 849 here).
0x04	4	Texture Width. Width of the texture in pixels.
0x08	4	Texture Height. Height of the texture in pixels.
0x0C	4	Depth.
0x10	4	Number of Mipmaps.
0x14	4	Texture Format. Go to line 589 on this page for explanation and format values.
0x18	4	AA Mode. Indicates the AA mode (number of samples) for the surface (see line 865 here).
0x1C	4	Usage. Indicates how the given surface may be used (see line 823 here).
0x20	4	Data Length. Length of texture data in bytes.
0x24	4	Data Pointer?
0x28	4	Mipmaps Data Length. Length of mipmaps data in bytes.
0x2C	4	Mipmaps Pointer?
0x30	4	Tile Mode. Indicates the desired tiling mode for the surface (see line 795 here).
0x34	4	Swizzle Value.
0x38	4	Alignment. Always 512 * bytes per pixel.
0x3C	4	Pitch.
0x40	0x0D	Mip Offset?. Offset for each mipmap?
0x4D	0x2B	Unknown. Mipmaps related? (Almost always 0 in textures with no mipmaps)
0x78	4	Number of Mipmaps. Again...
0x7C	4	Unknown. Always 0.
0x80	4	Unknown. Always 1.
0x84	4	Unknown. Always 0x00010203. (Is this some kind of a pattern? 00->01->02->03)
0x88	0x14	Unknown.

Swizzling

This code can swizzle image and mipmap data. Call swizzle() by giving it the width, height, format (in hex), tileMode, swizzle value, pitch and the swizzled data. If you're swizzling then set do_swizzle to True. If you're deswizzling then set do_swizzle to False.

Tools

The following tools can handle GTX/GSH files:

• GTX Extractor, by AboodXD