FMDL (File Format)

The FMDL (caFe MoDeL) model format is a format for models which appears as a subfile of a BFRES file in the 0th file group. Typically a BFRES file has one FMDL but some have none and some have more than one.

Format

An FMDL file begins with an FMDL header. This is then followed by a number of sections pointed to by the header, many of which can occur multiple times. The purpose of these sections is described in the table below. Unless otherwise noted, all offsets in BFRES files are relative to themselves, not the beginning of the file which is more common in other formats.

Section	Purpose
FVTX	Describes an array of array of vertices which can have a number of attributes including position, normal, colour and texture coordinates.
FMAT	Describes the properties of a surface necessary to draw it including texture information.
FSKL	Describes a skeleton for the model which may be used in animations.
FSHP	Selects triples of vertices from one FVTX section to draw triangles between. Also specifies the FMAT material and the FSKL attachment of the triangles.

Header (FMDL)

Every FMDL begins with an 0x30 byte FMDL header.

Offset	Size	Type	Description
0x00	4	Char[4]	"FMDL" file identifier, ASCII string.
0x04	4	Int32	File name offset (without file extension).
0x08	4	Int32	File path offset, the path of the file this data was originally created from. Stripped in Mario Kart 8 files, always pointing to an empty string at the end of the BFRES string table.
0x0C	4	Int32	FSKL offset. Offset to the FSKL Header.
0x10	4	Int32	FVTX array offset. Offset to the first element in an array of FVTX Headers.
0x14	4	Int32	FSHP index group offset. Offset to an index group which contains named pointers to FSHP Headers.
0x18	4	Int32	FMAT index group offset. Offset to an index group which contains named pointers to FMAT Headers.
0x1C	4	Int32	User Data index group offset. It is only used in a handful of Mario Kart 8 models to set the value of "ParticleLimit".
0x20	2	UInt16	FVTX count: number of FVTX sections in the FVTX array.
0x22	2	UInt16	FSHP count: number of FSHP sections in the the FSHP index group.
0x24	2	UInt16	FMAT count: number of FMAT sections in the the FMAT index group.
0x26	2	UInt16	User Data entry count.
0x28	4	UInt32	Total number of vertices to process.
0x2C	4	UInt32	User pointer, can be set at runtime, 0 in files.
0x30	End of FMDL header

FVTX

The model may have one or more FVTX (caFe VerTeX) sections which describe the vertices for one polygon (e.g. the road of a track). The section describes a series of buffers and attributes. Buffers are arrays of arbitrary elements which contain the actual values of the vertices and are passed directly to the graphics card. Attributes are properties of vertices (e.g. position, texture coordinate, vertex colours) and they describe the format and layout of the elements in the buffers.

Header (FVTX)

Each FVTX section has a 0x20 byte header. These headers are stored sequentially in an array at the offset given in the FMDL header. The length of this array is also given in that header.

Offset	Size	Type	Description
0x00	4	Char[4]	"FVTX" section identifier, ASCII string.
0x04	1	Byte	Attribute count: number of different attributes (position, normal, colour, etc) in the attribute array.
0x05	1	Byte	Buffer count: number of attribute buffers in the buffer array.
0x06	2	UInt16	Section index: index into FVTX array of this entry.
0x08	4	UInt32	Number of vertices. This is also the number of elements in each buffer.
0x0C	1	Byte	Vertex skin count, the number of bones influencing a vertex. Depending on the value, vertex positions are stored in different coordinate systems: 2+ indicates smooth skinning. Coordinates are relative to the model coordinate system of a rest pose. 1 indicates rigid skinning. Coordinates are relative to the local coordinate system of the bone at the index given by the blendindex0 vertex attribute. 0 indicates rigid bodies using no skinning. Coordinates are relative to the local coordinate system of the bone at the index given by the FSKL Bone skin index field in the FSHP header.
0x0D	3	—	Padding.
0x10	4	Int32	Attribute array offset. Offset to the first element in the Attribute array.
0x14	4	Int32	Attribute index group offset. Named pointers to the members of the Attribute array to allow named lookups.
0x18	4	Int32	Buffer array offset. Offset to the first element in the Buffer array.
0x1C	4	UInt32	User pointer, can be set at runtime, 0 in files.
0x20	End of FVTX header

Attributes

The attributes of each FVTX section are stored as a simple repeating 0xc byte structure. These are stored in an array with location and length specified by the FVTX header. They are also referenced by the attribute index group, presumably to allow both index and name based lookup of attributes.

Offset	Size	Type	Description
0x00	4	Int32	Attribute name offset (s. below).
0x04	1	Byte	Buffer index in the FVTX Buffer array of the buffer storing the data of this attribute (s. below).
0x05	1	—	Padding.
0x05	2	UInt16	Buffer offset of the attribute in each element in the buffer (in bytes).
0x08	4	UInt32	Format of the attribute's data in the buffer, maps to GX2AttribFormat (s. below).
0x0C	End of attribute

Attribute Name

Based on some of the shader code in /vol/content/mapobj/PackunMusic/PackunMusic.bfres the following naming convention seems to be used for attributes.

Attribute Name	Friendly Name	Description
_p0	position0	The position of the vertex.
_n0	normal0	The normal of the vertex used in lighting calculations.
_t0	tangent0	The tangent of the vertex used in advanced lighting calculations.
_b0	binormal0	The binormal of the vertex used in advanced lighting calculations.
_w0	blendweight0	Influence amount of the smooth skinning matrix at the index given in blendindex0.
_i0	blendindex0	Index of influencing smooth skinning matrix.
_u0	uv0	Texture coordinates used for texture mapping.
_u1	uv1
_u2	uv2
_u3	uv3
_c0	color0	Vertex colours used for simple shadow mapping.
_c1	color1

Buffer Index

Original files typically store all attributes into one buffer or each attribute into a separate buffer. Rarely more than 1 attribute is stored in one and remaining attributes in another buffer. The condition determining which way is chosen seems arbitrary and does not follow specific rules.

Format

The following formats are available in the GX2AttribFormat enum:

Value	Format	Data	Min	Max	Description
0x0000	unorm_8	One u8	0f	1f	Represents one u8 that is converted to one float.
0x0004	unorm_8_8	Two u8s	0f	1f	Represents two u8 that is converted to two floats.
0x0007	unorm_16_16	Two u16s	0f	1f	Represents two u16 that is converted to two floats.
0x000A	unorm_8_8_8_8	Four u8	0f	1f	Represents four u8 that is converted to four floats.
0x0100	uint_8	One u8	0x00	0xFF	Represents one u8 that is converted to one u32.
0x0104	uint_8_8	Two u8	0x00	0xFF	Represents two u8 that is converted to two u32.
0x010A	uint_8_8_8_8	Four u8	0x00	0xFF	Represents four u8 that is converted to four u32.
0x0200	snorm_8	One s8	-1f	1f	Represents one s8 that is converted to one float.
0x0204	snorm_8_8	Two s8	-1f	1f	Represents two s8 that is converted to two floats.
0x0207	snorm_16_16	Two s16	-1f	1f	Represents two s16 that is converted to two floats.
0x020A	snorm_8_8_8_8	Four s8	-1f	1f	Represents four s8 that is converted to four floats.
0x020B	snorm_10_10_10_2	Three s10	-1f	1f	Represents three s10 that is converted to three floats. The top two bits are always 0b01.
0x0300	sint_8	One s8	—	—	Represents one s8.
0x0304	sint_8_8	Two s8	—	—	Represents two s8.
0x030A	sint_8_8_8_8	Four s8	—	—	Represents four s8.
0x0806	float_32	One float	—	—	Represents one 32 bit floating point number.
0x0808	float_16_16	Two halfs	—	—	Represents two 16 bit floating point numbers that is converted to two floats.
0x080D	float_32_32	Two floats	—	—	Represents two 32 bit floating point numbers.
0x080F	float_16_16_16_16	Four halfs	—	—	Represents four 16 bit floating point numbers that is converted to four floats.
0x0811	float_32_32_32	Three floats	—	—	Represents three 32 bit floating point numbers.
0x0813	float_32_32_32_32	Four floats	—	—	Represents four 32 bit floating point numbers.

Buffers

The buffers of each FVTX section are stored as a repeating 0x18 byte header structure which references the actual data stored later in the BFRES file. The headers are stored in an array with location and length specified by the FVTX header.

Offset	Size	Type	Description
0x00	4	UInt32	Data pointer filled at runtime, always 0 in files.
0x04	4	UInt32	Size of the buffer in bytes.
0x08	4	UInt32	Buffer handle, filled at runtime, always 0 in files.
0x0C	2	UInt16	Stride, the size of each element in the buffer (always 0 for index buffers).
0x0E	2	UInt16	Buffering count, always 1. Multiplicator for the number of bytes reserved as buffer data at runtime.
0x10	4	UInt32	Context pointer filled at runtime as a pointer to GX2StreamOutContext, always 0 in files.
0x14	4	Int32	Data offset.
0x18	End of buffer

FMAT

The model may have one or more FMAT (caFe MATerial) sections which describe surface properties of a polygon such as textures. Every polygon is rendered using a vertex shader and a pixel shader. These are pieces of code which run on the graphics card. Like any code, these have parameters which is principally what the FMAT section controls. There are many different ways for the FMAT section to set variables in the shader code, but it remains unknown what the reason for this is. All shader parameters are either uniform or attributes. Attribute parameters vary per vertex or pixel, whereas uniform parameters are global. The FMAT must specify values for all uniform parameters, and specifies a mapping between vertex attributes in the corresponding FVTX sections and attribute parameters for both the pixel and vertex shader. In Mario Kart 8 most models reference the same pixel shader and the same vertex shader, both called Turbo_UBER. Turbo_UBER is totally generic and has hundreds of parameters to configure the rendering. The source code for Turbo_UBER seems to be available in /vol/content/mapobj/PackunMusic/PackunMusic.bfres.

Header (FMAT)

Every FMAT begins with an 0x4C byte header structure. This references the other structures documented here to describe the material.

Offset	Size	Type	Description
0x00	4	Char[4]	"FMAT" section identifier, ASCII string.
0x04	4	Int32	Material name offset.
0x08	4	UInt32	Material flags. Only bit 0 has a meaning, controlling the visibility of the material (visible if set).
0x0C	2	UInt16	Section index of this material.
0x0E	2	UInt16	Render info parameter count. Number of elements in the Render Info Parameter index group.
0x10	1	Byte	Texture Reference count. Number of elements in Texture Reference array.
0x11	1	Byte	Texture Sampler count. Number of elements in the Texture Sampler array. Always equal to the number of elements in the Texture Selector array.
0x12	2	UInt16	Material Parameter count. Number of elements in the Material Parameter array.
0x14	2	UInt16	Volatile Parameter count. Number of parameters handled as volatile, unknown purpose.
0x16	2	UInt16	Material Parameter data length. The size of the Material Parameter Data section in bytes.
0x18	2	UInt16	Raw Parameter data length, unknown purpose.
0x1A	2	UInt16	User Data entry count. User data in FMAT sections is apparently used to assign values to a shadow variable in the shader code. Shadow variables are always uniform variables.
0x1C	4	Int32	Render Info Parameter index group offset. Offset to the index group defining render info parameters.
0x20	4	Int32	Render State offset. Offset to the render state structure.
0x24	4	Int32	Shader Assign offset. Offset to the shader assign structure.
0x28	4	Int32	Texture Reference array offset. Each element points to FTEX file names and FTEX headers.
0x2C	4	Int32	Texture Sampler offset. Offset to the first element in the Texture Sampler array.
0x30	4	Int32	Texture Sampler index group offset. Offset to an index group which references the Texture Sampler array, to allow named value lookups.
0x34	4	Int32	Material Parameter array offset. Offset to the first element in the Material Parameter array.
0x38	4	Int32	Material Parameter index group offset. Offset to an index group which references the Material Parameter array, to allow named value lookups.
0x3C	4	Int32	Material Parameter data offset. Offset to the beginning of the values for Material Parameters. The Material Parameter array references this data.
0x40	4	Int32	User Data index group offset.
0x44	4	Int32	Volatile Flags data offset. Points to an array of Ceil((Material Parameter count) / 8) bytes, representing bits determining if a parameter is volatile. Unknown purpose.
0x48	4	Int32	User pointer, can be set at runtime, 0 in files.
0x4C	End of FMAT Header

Render Info Parameter

A Render Info Parameter is a repeating structure of at least 0x08 bytes, each of which describes an array of values to assign to a render info variable in the shader code. Render info variables are always uniform variables. The Render Info Parameter structures are referenced by the Render Info Parameter index group in the corresponding FMAT Header.

Offset	Size	Type	Description
0x00	2	UInt16	Array length, number of elements in the array. Always 0 or 1 in Mario Kart 8 files.
0x02	1	Byte	Type of each array element. Type Element Size Element Type 0 8 Vector of 2 signed integers. 1 8 Vector of 2 floats. 2 4 Offset to a string.
0x03	1	—	Padding.
0x04	4	Int32	Variable name offset.
0x08	Varies	Varies	Array data.
Varies	End of Render Info Parameter

Texture Sampler

A Texture Sampler is a repeating 0x18 byte structure each of which describes one of the inputs to the pixel shader from the selected textures. The length and position of the Texture Sampler array is specified by the corresponding FMAT Header.

Offset	Size	Type	Description
0x00	4	UInt32	First value of GX2Sampler structure. Bits packed as xxxJJJxx IIHHHGGF FxEExDDC CCBBBAAA. AAA maps to GX2TexClamp (line 880 here) and sets the clamping / repetition of the texture on the U axis. BBB maps to GX2TexClamp (line 880 here) and sets the clamping / repetition of the texture on the V axis. CC C maps to GX2TexClamp (line 880 here) and sets the clamping / repetition of the texture on the W axis (for 3D textures). DD maps to GX2TexXYFilterType (line 910 here) and sets the texture filtering on the U and V axes when the texture is drawn larger than the actual texture's resolution. EE maps to GX2TexXYFilterType (line 910 here) and sets the texture filtering on the U and V axes when the texture is drawn smaller than the actual texture's resolution. F F maps to GX2TexZFilterType (line 920 here) and sets the texture filtering on the W axis (for 3D textures). GG maps to GX2TexMipFilterType (line 931 here) and sets the texture filtering for mipmaps. HHH maps to GX2TexAnisoRatio (line 976 here) and controls the maximum anisotropic filtering level to use. II maps to GX2TexBorderType (line 896 here) and determines what color to draw at places not reached by a texture if the clamp mode does not repeat it. JJJ maps to GX2CompareFunction (line 105 here) and sets the depth comparison function.
0x04	4	UInt32	Second value of GX2Sampler structure. Bits packed as CCCCCCCC CCCCBBBB BBBBBBAA AAAAAAAA. AA AAAAAAAA is a 10-bit floating point value controlling the minimum LOD level. BBBB BBBBBB is a 10-bit floating point value controlling the maximum LOD level. CCCCCCCC CCCC is a 12-bit floating point value controlling the LOD bias. 10-bit values are stored unsigned. To get a float value, divide it by 64. 12-bit values are stored signed. To get the float value, divide the signed value by 64. 10-bit values have a range between 0 – 32 and 12-bit values have a range between -32 – 31.984375.
0x08	4	UInt32	Third value of GX2Sampler structure. Bits packed as xAxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx. A is a boolean controlling whether depth comparison is enabled. This should never be set on a real console.
0x0C	4	UInt32	Handle of the sampler, set at runtime.
0x10	4	Int32	Attribute name offset.
0x14	1	Byte	Index of this element.
0x15	3	—	Padding.
0x18	End of Texture Sampler

Based on the some of the shader code in /vol/content/mapobj/PackunMusic/PackunMusic.bfres the following naming convention seems to be used for texture attributes.

Attribute Name	Friendly Name	Description
_a0	albedo0	Ordinary colour textures for surface albedo.
_a1	albedo1
_a2	albedo2
_a3	albedo3
_s0	specular0	Specular highlight texture.
_n0	normal0	Normal map texture for altering surface normals.
_n1	normal1
_e0	emission0	Emissive lighting texture.
_b0	bake0	Shadow textures.
_b1	bake1

Material Parameter

A Material Parameter is a repeating 0x14 byte structure each of which describes the value to assign to a material variable in the shader code. Material variables are always uniform variables. The length and position of the Material Parameter array is controlled by the corresponding FMAT Header.

Offset	Size	Type	Description
0x00	1	Byte	Type of the variable (s. below).
0x01	1	Byte	Size of the value in bytes.
0x02	2	UInt16	Offset relative to the start of the Material Parameter Data section to the value.
0x04	4	Int32	Uniform variable offset, set at runtime, always -1 in files.
if BFRES version >= 3.4.0.0
0x08	4	UInt32	Conversion callback pointer, set at runtime, always 0 in files.
0x0C	2	UInt16	Parameter index into the Material Parameter array.
0x0E	2	UInt16	Same value as Parameter index again.
0x10	4	Int32	Variable name offset.
if BFRES version = 3.3.X.X
0x08	4	UInt32	Conversion callback pointer, set at runtime, always 0 in files.
0x0C	2	UInt16	Parameter index into the Material Parameter array.
0x0E	2	UInt16	Same value as Parameter index again.
0x10	4	Int32	FMAT offset.
0x14	4	Int32	Variable name offset.
if BFRES version < 3.3.0.0
0x08	4	Int32	Variable name offset.

The Type field can be one of the following:

Type	Size	Description
0	4	1 boolean value.
1	8	2-component boolean vector.
2	12	3-component boolean vector.
3	16	4-component boolean vector.
4	4	1 signed integer value.
5	8	2-component signed integer vector.
6	12	3-component signed integer vector.
7	16	4-component signed integer vector.
8	4	1 unsigned integer value.
9	8	2-component unsigned integer vector.
10	12	3-component unsigned integer vector.
11	16	4-component unsigned integer vector.
12	4	1 floating point value.
13	8	2-component floating point vector.
14	12	3-component floating point vector.
15	16	4-component floating point vector.
17	16	2×2 floating point matrix.
18	24	2×3 floating point matrix.
19	32	2×4 floating point matrix.
21	24	3×2 floating point matrix.
22	36	3×3 floating point matrix.
23	48	3×4 floating point matrix.
25	32	4×2 floating point matrix.
26	48	4×3 floating point matrix.
27	64	4×4 floating point matrix.
28	20	2D SRT data. Offset Size Type Description 0x00 8 Single[2] XY scaling 0x08 4 Single Rotation 0x0C 8 Single[2] XY translation
29	36	3D SRT data. Offset Size Type Description 0x00 12 Single[3] XYZ scaling 0x0C 12 Single[3] XYZ rotation 0x18 12 Single[3] XYZ translation
30	24	Texture SRT data. Offset Size Type Description 0x00 4 UInt32 SRT mode 0 specifies Maya SRT method. 1 specifies 3ds Max SRT method. 2 specifies Softimage SRT method. 0x04 8 Single[2] XY scaling 0x0C 4 Single Rotation 0x10 8 Single[2] XY translation
31	28	Texture SRT data which is then multiplied by a 3x4 matrix referenced by the matrix pointer. The structure is the same as above, but with a field added to store the pointer to the matrix in at runtime: Offset Size Type Description 0x18 4 UInt32 3x4 matrix pointer, set at runtime.

Matrices are encoded down columns then along rows, so a 2×3 identity matrix would be encoded 1, 0, 0, 1, 0, 0.

Render State

A Render State structure is a 0x30 byte structure controlling if and how polygons are drawn. A Render State structure is referenced by the corresponding FMAT Header.

Offset	Size	Type	Description
0x00	4	UInt32	Flags. Controls how polygons are affecting the depth buffer and how they are blended / composed. A mode and blend value have to be combined to form valid flags. Type Bits (0-based) Description Mode - Custom Mode 0 Opaque Mode 1 Alpha Mask Mode 0 & 1 Translucent Blend - None Blend 4 Color Blend 5 Logical
0x04	4	UInt32	Polygon control, maps to GX2PolygonControlReg, a bitset packed as xxxxxxxx xxxxxxxx xxIHGFFF EEEDDCBA. Beyond other features, it most prominently controls culling and cull order of polygons. A controls whether front faces are culled. B controls whether back faces are culled. C maps to GX2FrontFaceMode and determines the order in which vertices have to form the triangle to be handled as a front rather than back face. The order can be clockwise (1) or counter-clockwise (0). DD configures whether polygons are drawn at all (1) or not (0) EEE maps to GX2PolygonMode and determines how front facing polygons are drawn. This can be set to draw only points (0), lines (1) or full triangles (2). FFF is the same as EEE, but for back facing polygons. G configures polygon depth offsets for front facing polygons (useful to create decals without Z fighting). H is the same as G but for back facing polygons. I is the same as G but for lines and points.
0x08	4	UInt32	Depth control, maps to GX2DepthStencilControlReg, a bitset packed as MMMLLLKK KJJJIIIH HHGGGFFF EDDDxCBA. Controls depth and stencil buffer value comparison and action before writing new data to buffers. A controls whether stencil testing is enabled (1) or not (0). B controls whether depth testing is enabled (1) or not (0). C controls whether writing to the depth buffer is enabled (1) or not (0). DDD maps to GX2CompareFunction and configures when a fragment is allowed to overwrite the old value in the depth buffer with a new one (the depth buffer comparison function) (line 105 here). E controls whether back faces can write to the stencil buffer (1) or not (0). FFF controls the front face stencil buffer comparison function, maps to GX2CompareFunction aswell (s. DDD). GGG maps to GX2StencilFunction and configures what to do with the existing stencil value when the stencil comparison function fails for front facing polygons (line 121 here). HH H is the same as GGG, but taking effect when the stencil test passes with the depth buffer. III is the same as GGG, but taking effect when the stencil test fails with the depth buffer. JJJ is the same as FFF, but for back faces. K KK is the same as GGG, but taking effect when the stencil test fails for back faces. LLL is the same as GGG, but taking effect when the stencil test passes for back faces with the depth buffer. MMM is the same as GGG, but taking effect when the stencil test fails for back faces with the depth buffer.
0x0C	8	UInt32 / Single	Alpha test, maps to GX2AlphaTestReg, a structure of an unsigned integer and a floating point value. Controls how alpha colors are written to buffers. The unsigned integer is a bitset packed as xxxxxxxx xxxxxxxx xxxxxxxx xxxxBAAA. AAA maps to GX2CompareFunction and determines when alpha fragments should be written. B determines whether alpha testing is enabled at all (line 105 here). Floating point reference value always less than 1.0f in Mario Kart 8 files.
0x14	4	UInt32	Color control, maps to GX2ColorControlReg, a bitset packed as xxxxxxxx DDDDDDDD CCCCCCCC xBBBxxxA. Controls how colors are written to buffers. A controls whether multiwrites are enabled (1) or not (0). BBB controls a special operation and is used to enable a color buffer with unknown purpose. CCCCCCCC controls the bitmask used for blending. DDDDDDDD maps to GX2LogicOp and determines the ROP3 color logic operation (line 161 here) Defaults to Copy operation and nothing else enabled. Some files set a bitmask of 00000001.
0x18	8	UInt32[2]	Blend control, maps to GX2BlendControlReg, a structure of two unsigned integers. Controls how and to which target blending is performed. The first unsigned integer describes the target index (always 0 in Mario Kart 8 files), the second is a bitset packed as xxGFFFFF EEEDDDDD xxxCCCCC BBBAAAAA. AAAAA maps to GX2BlendFunctionand sets the color source blend operation (line 189 here). BBB maps to GX2BlendCombine and sets the color combine operation (line 231 here). CCCCC is the same as AAAAA but sets the color destination blend operation. DDDDD is the same as AAAAA, but sets the alpha source blend operation. EEE is the same as BBB, but sets the alpha combine operation. FFFFF is the same as AAAAA, but sets the alpha destination blend operation. G apparently controls whether to separate the alpha from color blending. Blend value always 0x20010101, 0x20010104, 0x20010501 or 0x20010504 in Mario Kart 8 files.
0x20	16	Single[4]	Blend color, maps to GX2BlendConstantColorReg. Controls the blend color as 4 RGBA floating point values. Defaults to (0f, 0f, 0f, 0f).
0x30	End of Render State

Shader Assign

A Shader Assign structure is a 0x1C byte structure which describe the shader to be used by a material. A Shader Assign structure is referenced by the corresponding FMAT Header.

Offset	Size	Type	Description
0x00	4	Int32	Shader archive name offset.
0x04	4	Int32	Shading model name offset.
0x08	4	UInt32	Revision. Apparently unused, always 0 or 1.
0x0C	1	Byte	Vertex Shader Input count. Number of elements in the Vertex Shader Input index group.
0x0D	1	Byte	Pixel Shader Input count. Number of elements in the Pixel Shader Input index group.
0x0E	2	UInt16	Parameter count. Number of elements in the Parameter index group.
0x10	4	Int32	Vertex Shader Input index group offset. Offset to the index group which forms a mapping between strings, mapping an FVTX attribute to a vertex shader variable. Normally the names are always the same in Mario Kart 8, so this mapping is just ["_p0": "_p0", "_n0": "_n0", ...]?
0x14	4	Int32	Pixel Shader Input index group offset. Offset to the index group which forms a mapping between strings, mapping an FVTX attribute to a pixel shader variable. Normally the names are always the same in Mario Kart 8, so this mapping is just ["_p0": "_p0", "_n0": "_n0", ...]?
0x18	4	Int32	Parameter index group offset. Offset to the index group which forms a mapping between strings, mapping a uniform shader variable to a value. The values are always strings, even for numeric parameters.
0x1C	End of Shader Assign

FSKL

Each model has one FSKL (caFe SKeLeton) section which describes one or more bones. The bones form a skeleton and give a transformation to apply to any attached polygon. Every FSHP polygon is attached to at least one bone. The FSKL format is somewhat different in BFRES files with values other than 0x03040004 after the FRES identifier, which may indicate an alternative version of the format. These are rare in Mario Kart 8 and not documented here.

Header (FSKL)

The FSKL section always starts with an 0x24 byte header. The location of this header is given by the offset in the FMDL header.

Offset	Size	Type	Description
0x00	4	Char[4]	"FSKL" section identifier, ASCII string.
0x04	4	UInt32	Flags. Controls how scaling and rotation is performed. Encoded as xxxxxxxx xxxxxxxx xxxRxxSS xxxxxxxx bits. SS specifies how the bone matrix is calculated: Value Description 0 No scaling 1 Standard scaling. Results in a "default" scaling method. 2 Maya scaling. Respects Maya's segment scale compensation which offsets child bones rather than scaling them with the parent. 3 Softimage scaling. Respects the scaling method of Softimage. R controls the rotation mode, either euler XYZ rotation (bit set) or quaternion (bit unset). Always 0x00001100 (standard scaling & euler XYZ rotation) or 0x00001200 (Maya scaling & euler XYZ rotation) in Mario Kart 8 files.
0x08	2	UInt16	Bone array count. Number of elements in the Bone array.
0x0A	2	UInt16	Smooth Index array count. Number of elements in the Smooth Matrix array for smooth skinning (shape vertices are influenced by multiple bones).
0x0C	2	UInt16	Rigid Index array count. Number of elements in the Rigid Matrix array at the end of the Smooth Index array for rigid skinning (shape vertices are influenced by a single bone).
0x0E	2	—	Padding.
0x10	4	Int32	Bone index group offset. Named pointers to the members of the Bone array to allow named lookups.
0x14	4	Int32	Bone array offset. Offset to the first element in the Bone array.
0x18	4	Int32	Smooth Index array offset. Offset to the first element in the Smooth Index array. Always given even if the array is empty.
0x1C	4	Int32	Smooth Matrix array offset. Offset to the first element in the Smooth Matrix array. Always given even if the array is empty.
0x20	4	UInt32	User pointer, can be set at runtime, 0 in files.
0x24	End of FSKL header

Bone

A Bone is a repeating 0x40 byte structure which descibes a transformation to apply to a polygon. Each bone has up to four parents, which form a tree called a skeleton. To compute the final transformation of a point, apply the transformation required by the bone it is attached to, then that bone's parent recursively up until no parents remain. The Bone tree is stored as an array with offset and length specified by the FSKL header.

Offset	Size	Type	Description
0x00	4	Int32	Name offset for this bone.
0x04	2	UInt16	Bone index of this bone into the bone array.
0x06	2	UInt16	Parent index of the parents to this bone. 0xFFFF for no parent.
0x08	2	Int16	Smooth Matrix index to reverse the transformation of this bone. -1 for no smooth matrix.
0x0A	2	Int16	Rigid Matrix index with unknown purpose. -1 for no rigid matrix.
0x0C	2	Int16	Billboard index to control how billboarded bones are affected in a hierarchy. -1 if no billboarded bones are affected.
0x0E	2	UInt16	User Data entry count.
0x10	4	UInt32	Flags, encoded as CCCCTTTT TxxxxBBB xxxRxxxx xxxxxxxV bits. V controls the visibility of the influenced shape. R controls the rotation mode, either euler XYZ rotation (bit set) or quaternion (bit unset). BBB controls how billboarded bones are projected: Value Description 0 No billboarding. The influenced shape is not transformed for billboarding. 1 Child billboarding. 2 World View Vector. The Z axis is parallel to the camera. 3 World View Point. The Z axis is equal to the direction the camera is pointing to. 4 Screen View Vector. The Z axis is parallel to the camera, the Y axis is equal to the up vector of the camera. 5 Screen View Point. The Z axis is equal to the direction the camera is pointing to, the Y axis is equal to the up vector of the camera. 6 Y-Axis View Vector. The Z axis has been made parallel to the camera view by rotating the Y axis. 7 Y-Axis View Point. The Z axis has been made equal to the direction the camera is pointing to by rotating the Y axis. T TTTT are combinable flags controlling how bones are transformed. Value Description 1 Segment scale compensation. Set for bones scaled in Maya whose scale is not applied to child bones. 2 Scale uniformly. 4 Scale volume by 1. 8 No rotation. 16 No translation. CCCC controls the same but for a hierarchy of bones. Value Description 1 Scale uniformly. 2 Scale volume by 1. 4 No rotation. 8 No translation. Always 0x00001001 (visible & euler XYZ rotation) in Mario Kart 8 files.
0x14	12	Single[3]	Scale Vector 3 floats. The amount to scale the vertices by.
0x20	16	Single[4]	Rotation Vector, either stored as euler rotation (X, Y, Z in radians) or a quaternion, depending on the bone Flags. Mario Kart 8 always uses euler XYZ rotation, so the last float is always set to 1f.
0x30	12	Single[3]	Translation Vector 3 floats. The amount to translate the vertices by.
0x3C	4	Int32	User Data index group offset. Never used in Mario Kart 8 FSKL sections and thus 0.
0x40	End of Bone

Smooth Matrix

The FSKL may specify an Smooth Matrix for any Bone. It does this by creating an entry in the Inverse Index array which is the index of the bone, and in the corresponding place in the Smooth Matrix array it places a 4×3 transformation matrix which reverses the full transformation of the bone and all its parents. Smooth Matrices are optional, it is Unknown if they are ever referenced. The position of and number of elements in the Smooth Matrix array and the Smooth Index array are given in the FSKL Header.

Rigid Matrix

At the end of the Smooth Index array are a number of indices for Rigid Matrices, which have Unknown purpose. The number of such Rigid Matrices is also present in the FSKL Header.

FSHP

The model may have one or more FSHP (caFe SHaPe) sections which describe the one polygon (e.g. the road of a track). The FSHP section consists of an 0x40 byte header, which references an FVTX section and indices of the polygons to draw. A basic FSHP amounts to a list of indices into the corresponding FVTX indicating which points to draw triangles between. The FSHP also references an FMAT to describe the material of the triangles, and an FSKL to indicate the bone structure of the model used in animation.

The triangles in an FSHP are organised by two systems; LoD Models and Visibility Groups. No model in Mario Kart 8 uses both of these features non-trivially simultaneously. LoD stands for Level of Detail, which is a standard performance technique used across many 3d rendering systems. Each LoD model is a simpler version of the one before it, with extraneous triangles removed, and finer detail simplified. As the camera in the game moves away from a polygon, the simpler version of the model is rendered instead, which should look the same as the fine detailed version at a distance. A trivial polygon will only have one LoD model, which will be rendered no matter what distance the camera is. Separately, the Visibility Group system allows parts of the model to not be rendered if they are off-screen. This allows an polygon which is partially off-screen to be rendered faster, by skipping the off-screen components. A trivial polygon will only have one Visibility Group, which will always be rendered.

Header (FSHP)

Every FSHP begins with an 0x40 byte header. This references other data structures which describe the polygon.

Offset	Size	Type	Description
0x00	4	Char[4]	"FSHP" section identifier, ASCII string.
0x04	4	Int32	Polygon name offset.
0x08	4	UInt32	Flags with only the following meaning: Bit (0-based) Description 1 Has vertex buffer. Always set (thus 2) in Mario Kart 8 files.
0x0C	2	UInt16	Section index or FVTX index. In every Mario Kart 8 model these numbers are the same.
0x0E	2	UInt16	FMAT index. Index of the material for this polygon.
0x10	2	UInt16	FSKL index of the bone for this polygon.
0x12	2	UInt16	Section index or FVTX index. In every Mario Kart 8 model these numbers are the same.
0x14	2	UInt16	FSKL Bone skin index. Specifies the index of the bone to which local coordinate matrix vertices are relative in case of rigid bodies using no skinning.
0x16	1	Byte	Vertex skin count, the number of bones influencing a vertex. Depending on the value, vertex positions are stored in different coordinate systems: 2+ indicates smooth skinning. Coordinates are relative to the model coordinate system of a rest pose. 1 indicates rigid skinning. Coordinates are relative to the local coordinate system of the bone at the index given by the blendindex0 vertex attribute. 0 indicates rigid bodies using no skinning. Coordinates are relative to the local coordinate system of the bone at the index given by the FSKL Bone skin index field.
0x17	1	Byte	LoD Model count. Number of elements in the array.
0x18	1	Byte	Key Shape count. This feature is not used in Mario Kart 8, thus always 0.
0x19	1	Byte	Target Attribute count. This feature is not used in Mario Kart 8, thus always 0.
0x1A	2	UInt16	Visibility Group Tree Node count.
0x1C	4	Single	Radius of spherical bounding box.
0x20	4	Int32	FVTX offset to the vertex buffer for this polygon.
0x24	4	Int32	LoD Model offset. Offset to the first element in the array.
0x28	4	Int32	FSKL Index array offset. Each element of this array is a 16 bit index.
0x2C	4	Int32	Key Shape index group offset. Never used in Mario Kart 8 and thus 0.
0x30	4	Int32	Visibility Group Tree Nodes offset.
0x34	4	Int32	Visibility Group Tree Ranges offset.
0x38	4	Int32	Visibility Group Tree Indices offset.
0x3C	4	UInt32	User pointer, can be set at runtime, 0 in files.
0x40	End of FSHP header

LoD Model

A LoD Model is a repeating 0x1C byte structure which are stored in a sequential array with location and size specified by the FSHP Header. Their purpose is described at the beginning of this section.

Offset	Size	Type	Description
0x00	4	UInt32	Primitive Type, maps to GX2PrimitiveType (line 527 here). Determines how index lists are interpreted to form triangles. Always GX2_PRIMITIVE_TRIANGLES (thus 4) in Mario Kart 8 files.
0x04	4	UInt32	Index Format, maps to GX2IndexFormat (line 515 here). The data type of indices. Always GX2_INDEX_FORMAT_U16 (thus 4) in Mario Kart 8 files.
0x08	4	UInt32	Count of points drawn in all Visibility Groups, thus the maximum number of points drawn at this LoD.
0x0C	2	UInt16	Visibility Group count. The number of elements in the array.
0x0E	2	—	Padding.
0x10	4	Int32	Visibility Group offset to the first element in the array.
0x14	4	Int32	Index Buffer offset.
0x18	4	UInt32	Skip vertices, the number of elements to skip in the corresponding FVTX buffer.
0x1C	End of LoD Model

Visibility Group

A Visibility Group is a repeating 0x08 byte structure describing an offset and a count in the corresponding Index Buffer. Visibility Groups are stored in a sequential array with location and count indicated by the corresponding LoD Model. This allows multiple visibility groups to use the same Index Buffer. In many cases, a single group is used which simply draws the entire Index Buffer.

Offset	Size	Type	Description
0x00	4	UInt32	Offset into index buffer in bytes.
0x04	4	UInt32	Count of the points to draw.
0x08	End of Visibility Group

Index Buffer

An Index Buffer is an 0x18 byte structure which describes a list of values (of type as given in the header) which are used to index the FVTX section when drawing the polygon. Index Buffers are referenced by LoD Models. They are instances of the same structure as FVTX Buffers and thus have the same layout.

Visibility Group Tree

The Visibility Group Tree is some sort of tree structure that occurs in all FSHP sections. In all Mario Kart 8 files, when the FSHP has multiple LoD Models, the Visibility Group Tree is a trivial one node tree. The Visibility Group Tree is used to control which Visibility Groups need to be drawn as described at the beginning of this section. The workings of the structure are however unknown.

Nodes

The Visibility Group Tree Node is a repeating 0x0C byte structure. The nodes form a binary tree. The FSHP header contains a pointer to node array, as well as specifying its length. The root node is the first node in this array. Each node specifies a range of Visibility Groups, with the root node always covering all nodes, and the children of each node always selecting disjoint subsets of that node's range.

Offset	Size	Description
0x00	2	Left child index. The current node's index if it has no left child.
0x02	2	Right child index. The current node's index if it has no right child.
0x04	2	Unknown, always the same as Left child index.
0x06	2	Next sibling index. For left children, always the current node's parent's right child (the current node's index if it has no right child).
0x08	2	Visibility Group index selects a range of Visibility Groups along with the count.
0x0A	2	Visibility Group count selects a range of Visibility Groups along with the index.
0x0C	End of Node

Ranges

The Visibility Group Tree Range is a repeating 0x18 byte structure. There are exactly as many Ranges as Nodes. The range contains two 3D vectors defining a bounding box.

Offset	Size	Type	Description
0x00	12	Single[3]	Center 3D position (X,Y,Z float).
0x0C	12	Single[3]	Extent from the center position (X,Y,Z float).
0x18	End of Range

Note that in older BFRES versions, the vectors specify minimum and maximum points of the bounding boxes rather than center and extent.

Indices

The Visibility Group Tree Index array is an array of 16 bit values which appear to be the index of the leaf node of the Visibility Group Tree which contains the corresponding Visibility Group. Therefore this array has length equal to the number of Visibility Groups in the FSHP section.