FMDL (File Format)

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The FMDL 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.
Parameter Sets a named paramter for the model.

Header (FMDL)

Every FMDL begins with an 0x2c byte FMDL header.

Offset Size Description
0x00 4 "FMDL" file identifier, ASCII string.
0x04 4 File name offset (without file extension).
0x08 4 End of BFRES string table offset.
0x0c 4 FSKL offset.
0x10 4 FVTX array offset.
0x14 4 FSHP index group offset.
0x18 4 FMAT index group offset.
0x1c 4 Parameter index group offset. May be 0 if no parameters exist (common).
0x20 2 FVTX count: number of FVTX sections.
0x22 2 FSHP count: number of FSHP sections.
0x24 2 FMAT count: number of FMAT sections.
0x26 2 Parameter count: number of parameter sections.
0x28 4 Unknown possibly something like an unused face count.
0x2c End of FMDL header

FVTX

The model may have one or more FVTX 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 arbitrary pieces of data 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 data 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 Description
0x00 4 "FVTX" section identifier, ASCII string.
0x04 1 Attribute count: number of different attributes in section (position, normal, colour, etc).
0x05 1 Buffer count: number of attribute buffers.
0x06 2 Section index: index into FVTX array of this entry.
0x08 4 Number of vertices.
0x0c 1 Unknown; values seen are between 0 and 4 (normally 0).
0x0d 3 Unknown always 0.
0x10 4 Attribute array offset.
0x14 4 Attribute index group offset.
0x18 4 Buffer array offset.
0x1c 4 Padding, always 0.
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 Description
0x00 4 Attribute name offset.
0x04 1 Buffer index of the buffer containing this attribute.
0x05 3 Buffer offset of the attribute in each structure in the buffer.
0x08 4 Format of the attribute's data in the buffer.
0xc End of attribute

Based on the 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 as used in lighting calculations.
_t0 tangent0 The tangent of the vertex as used in advanced lighting calculations.
_b0 binormal0 The binormal of the vertex as used in advanced lighting calculations.
_w0 blendweight0 unknown
_i0 blendindex0 unknown
_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

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 Description
0x00 4 Unknown always 0.
0x04 4 Size of the buffer in bytes.
0x08 4 Unknown always 0.
0x0c 2 Stride: the size of each element in the buffer.
0x0e 2 Unknown always 1.
0x10 4 Unknown always 0.
0x14 4 Data offset.
0x18 End of buffer

FSHP

The model may have one or more FSHP 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.

Header (FSHP)

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

Offset Size Description
0x00 4 "FSHP" section identifier, ASCII string.
0x04 4 Polygon name offset.
0x08 4 Unknown always 2.
0x0c 2 Section Index or FVTX Index. In every Mario Kart 8 model these numbers are the same.
0x0e 2 FMAT Index. Index of the material for this polygon.
0x10 2 FSKL Index of the bone for this polygon.
0x12 2 Section Index or FVTX Index. In every Mario Kart 8 model these numbers are the same.
0x14 2 FSKL Index Array Count. Often zero, Unknown purpose but seems to be related to FSKL.
0x16 1 Unknown: If FSKL Index Array is present this tends to be non-zero. Zero otherwise.
0x17 1 Drawing Command count. Number of elements in the array.
0x18 4 Drawing Extent Tree Node count.
0x1c 4 Unknown floating point.
0x20 4 FVTX offset to the vertex buffer for this polygon.
0x24 4 Drawing Command offset. Offset to the first element in the array.
0x28 4 FSKL Index Array Offset. Each element of this array is a 16 bit index.
0x2c 4 Unknown always 0.
0x30 4 Drawing Extent Tree Nodes offset.
0x34 4 Drawing Extent Tree Ranges offset.
0x38 4 Drawing Extent Tree Indices offset.
0x3c 4 Unknown always 0.
0x40 End of FSHP header

Drawing Command

A Drawing Command is a repeating 0x18 byte structure which are stored in a sequential array with location and size specified by the FSHP Header

Offset Size Description
0x00 4 Unknown Always 4.
0x04 4 Unknown Always 4.
0x08 4 Count of points drawn in all Drawing Extents.
0x0c 2 Drawing Extent count. The number of elements in the array.
0x0e 2 Unknown Always 0.
0x10 4 Drawing Extent offset. Offset to the first element in the array.
0x14 4 Index Buffer offset.
0x18 4 Vertex offset: the number of elements to skip in the corresponding FVTX buffer.
0x1c End of Drawing Command

Drawing Extent

A Drawing Extent is a repeating 0x8 byte structure describing an offset and a count in the corresponding Index Buffer. Drawing Extents are stored in a sequential array with location and count indicated by the corresponding Drawing Command. This allows multiple separate drawing commands to be issued using the same Index Buffer. In many cases, a single extent is used which simply draws the entire Index Buffer.

Offset Size Description
0x00 4 Offset into index buffer in bytes.
0x04 4 Count of the points to draw.
0x08 End of Drawing Extent

Index Buffer

An Index Buffer is an 0x18 byte structure which describes a list of 16 bit values which are used to index the FVTX section when drawing the polygon. Index Buffers are referenced by Drawing Commands. The format is very similar to the FVTX Buffer format, which may indicate they are instances of the same structure.

Offset Size Description
0x00 4 Unknown Always 0.
0x04 4 Size of index data in bytes.
0x08 4 Unknown Always 0.
0x0c 2 Unknown Always 0.
0x0e 2 Unknown Always 1.
0x10 4 Unknown Always 0.
0x14 4 Index data offset.
0x18 End of Index Buffer

Drawing Extent Tree

The Drawing Extent Tree is some sort of tree structure that occurs in all FSHP sections. In all Mario Kart 8 files, when the FSHP has multiple Drawing Commands, the Drawing Extent Tree is a trivial one node tree. The Drawing Extent Tree may be used to control which Drawing Extents need to be drawn, for example as part of a dynamic level of detail system. The true workings and purpose of the structure are however unknown.

Nodes

The Drawing Extent Tree Node is a repeating 0xc 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 Drawing Extents, 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. Always the current node's parent's right child (the current node's index if it has no right child).
0x08 2 Drawing Extent Index selects a range of Drawing Extents along with the count.
0x0a 2 Drawing Extent Count selects a range of Drawing Extents along with the index.
0x0c End of Node

Ranges

The Drawing Extent Tree Range is a repeating 0x18 byte structure. The purpose is unknown. There are exactly as many Ranges as Nodes. The range appears to contain two 3D positions, which are not necessarily distinct.

Offset Size Description
0x00 12 Unknown 3D position (x,y,z float).
0x0c 12 Unknown 3D position (x,y,z float).
0x18 End of Range

Indices

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