GTX\GSH (File Format)

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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.
0x0C 4 Minor version number.
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.
if Gfx2 version = 6.x (not confirmed yet)
0x0A Follows this block header the GX2 Surface.
0x0B Follows this block header the swizzled image data.
0x0C Follows this block header the swizzled mipmaps data.
0x0D Follows this block header Compute shader header.
0x0E Follows this block header Compute shader program.
0x0F Treated like a 0x02 block, users can do what they want with this block.
if Gfx2 version = 7.x
0x0A Same as 0x09? (Duplicate?)
0x0B Follows this block header the GX2 Surface.
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.

GX2 Surface

The GX2 Surface has an exact size of 0x9C:

Offset Size Type Description
0x00 4 UInt32 Dimension. Maps to GX2SurfaceDim (line 849 here). Indicates the "shape" of a given surface or texture.
0x04 4 UInt32 Texture width. Width of the texture in pixels.
0x08 4 UInt32 Texture height. Height of the texture in pixels.
0x0C 4 UInt32 Texture depth.
0x10 4 UInt32 Number of mipmaps.
0x14 4 UInt32 Texture format. Maps to GX2SurfaceFormat (line 589 here for explanation and format values).
0x18 4 UInt32 AA mode. Maps to GX2AAMode (line 865 here). Indicates the AA mode (number of samples) for the surface.
0x1C 4 UInt32 Usage. Maps to GX2SurfaceUse (line 823 here). Indicates how the given surface may be used.
0x20 4 UInt32 Data length. Length of texture data in bytes.
0x24 4 UInt32 Data pointer. Set at runtime.
0x28 4 UInt32 Mipmaps data length. Length of mipmaps data in bytes.
0x2C 4 UInt32 Mipmaps pointer. Set at runtime.
0x30 4 UInt32 Tile mode. Maps to GX2TileMode (line 795 here). Indicates the desired tiling mode for the surface.
0x34 4 UInt32 Swizzle value.
0x38 4 UInt32 Alignment. Always 512 * bytes per pixel.
0x3C 4 UInt32 Pitch.
0x40 0x34 UInt32[13] Mipmap offsets. An array of 13 offsets for each mipmap, relative to the start of the mipmap data.
0x74 4 UInt32 First mipmap.
0x78 4 UInt32 Number of mipmaps (again).
0x7C 4 UInt32 First slice. Always 0.
0x80 4 UInt32 Number of slices. Always 1.
0x84 4 Byte[4] Component Selector, determines which texture color channels are used for each target channel. The bytes map to the Red, Green, Blue and Alpha channel and can receive one of the following channels.
Value Name Description
0 R The channel will receive the red values of the texture.
1 G The channel will receive the green values of the texture.
2 B The channel will receive the blue values of the texture.
3 A The channel will receive the alpha values of the texture.
4 0 The channel will always have a value 0.
5 1 The channel will always have a value 1.
0x88 0x14 UInt32[5] Texture registers. Array of 5 unsigned integers with unknown purpose.

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: