MT5

MT5 is an model container format for Shenmue I.
The model format is based on an node based hierarchy tree.

For an C# implementation based on this documentation look here.

Header

Position	Length	Type	Description
0x00	0x04	string	Identifier (HRCM)
0x04	0x04	uint	TEXD offset
0x08	0x04	uint	First node offset

HRCM Format

The image above shows the general format of the HRCM(.mt5) model format used in Shenmue. The file is broken down into three major sections, the header, model data and texture data. The header is given in the first 12 bytes of the file and provides three values and uint32_t. The first value is the magic number of 'HRCM' indicating the model format. The second value is the offset to the texture data (provided as a list of embedded .pvr images). The third value is the offset to the first node (bone) definition for the model data.

typdef struct {
  uint32_t magic;
  uint32_t texd_ofs;
  uint32_t node_ofs;
} Mt5_Header_t;

MT5 Node

Position	Length	Type	Description
0x00	0x04	uint	ID
0x04	0x04	uint	Mesh offset
0x08	0x0C	short	Rotation (X, Y, Z)
0x14	0x0C	float	Scale (X, Y, Z)
0x20	0x0C	float	Position/Translate (X, Y, Z)
0x2C	0x04	uint	Child offset
0x30	0x04	uint	Sibling offset
0x34	0x04	uint	Parent offset
0x38	0x04	string	Node name
0x3C	0x04	?	Reserved

Mesh Data

Position	Length	Type	Description
0x00	0x04	uint	Polytype?
0x04	0x04	uint	Vertices offset
0x08	0x04	uint	Vertex count
0x0C	0x04	uint	Instructions offset
0x10	0x0C	float	Mesh center (X, Y, Z)
0x1C	0x04	float	Mesh radius

Instructions

These instructions are state machine like. Each instruction changes the state of how to render the strip.
Each instruction identifier is 2 bytes long.

• Instructions can act as padding (2 bytes)
• Instructions can be followed by a single 2 byte value (4 bytes)
• Otherwise instructions can provide a list of values of (n) bytes in which the length of the chunk follows the instruction.

Unused (0x0E00, 0x0F00)

Ignored. Skip 10 bytes.

0x0E00 is likely the material definition

• [ 0x0e00 (2) ] [ 0x08 (2) ] [ 0xffffffff (4) ][ 0x000000ff (4) ]
• The material definition is often given by the format above.
• The instruction for 0x0e00 is provided
• The length of the chunk is declared (static 8 value)
• The value of 0xffffffff is likely diffuse color rgba(255, 255, 255, 1.0);
• The value of 0x000000ff is likely ambient color rgba(0,0,0,1);

Note:
Since the color is only ever white, this effectively means the texture is applied directly. This hypothesis can be tested by changing these values to see if it changes the tint of the characters in game.

Unused (0x8000, 0xA000)

Ignored. Skip 2 bytes.

UV Size (0x0B00)

Size of the as UV which divides the raw UV value being read.
Only usable for non-UVH coordinates.

[ 0x0B00 (2) ] [ UV Size 0x400 (2) ]

Strip Attributes (0x0200 - 0x0700)

First byte holds UV flag for how they are interpreted. Holds information about the texture UV wrap modes.

Texture (0x0900)

Sets the texture to use for the next instructions.

[ 0x0900 (2) ] [ Texture Id (2) ]

Strip Group (0x1000 - 0x1400, 0x1800 - 0x1C00)

Position	Length	Type	Description
0x00	0x02	ushort	Strip count

These strip groups have the following vertex structure based on the identifiers:

Identifier	Vertex Size	Description
0x1000, 0x1300, 0x1800, 0x1B00	2 Bytes (Index)	Vertex index
0x1200, 0x1A00	2 Bytes (Index) + 4 Bytes (BGRA)	Vertex index, Color
0x1100, 0x1900	2 Bytes (Index) + 4 Bytes (UV)	Vertex index, UV
0x1400, 0x1C00	2 Bytes (Index) + 4 Bytes (UV) + 4 Bytes (BGRA)	Vertex index, UV, Color

• The index values in each strip group are defined locally to the weighted vertices being defined with the mesh group.
• Negative index values are defined as relative to the end of the parent node's vertex list

Strip

Position	Length	Type	Description
0x00	0x02	short	Strip vertex count

Sometimes the vertex count can be negativ, just abs() it.
The reason for this behavior is to indicate the wind direction of the first triangle when converting from strips to triangles.

let clockwise = stripLen < 0;
for (let i = 0; i < strip.length - 2; i++) {
    let a, b, c;

    if (clockwise && i % 2 === 0) {
        a = strip[i + 1];
        b = strip[i + 0];
        c = strip[i + 2];
    } else {
        a = strip[i + 0];
        b = strip[i + 1];
        c = strip[i + 2];
    }

    let face = new THREE.Face3(a.i, b.i, c.i);
    face.materialIndex = texId;
    this.faces.push(face);

    let auv = new THREE.Vector2(a.u, a.v);
    let buv = new THREE.Vector2(b.u, b.v);
    let cuv = new THREE.Vector2(c.u, c.v);

    this.faceVertexUvs.push([auv, buv, cuv]);
}

Strip "Vertex"

Type	Size	Description
short	0x02	Vertex index
short	0x04	(optional) Texture Coordinate (UV)
byte	0x04	(optional) BGRA8888 Color

The vertex structure is based on the strip group identifier.
Often the vertex index can be negativ, this is an optimization and is used to point to the parents vertices.
The UV coordinates are UVH (UV high-resolution) and need to be divided by 1024 to get normalized UV coordnates.

End (0x0080)

Defines the end of instructions.

Vertices

The vertices only hold the position and normal of an vertex.

Vertex

Position	Length	Type	Description
0x00	0x0C	float	Position (X, Y, Z)
0x0C	0x0C	float	Normals (X, Y, Z)

TEXD (Texture Definition)

This sections holds texture count for the model.

Position	Length	Type	Description
0x00	0x04	string	Identifier (TEXD)
0x04	0x04	uint	Size in bytes
0x08	0x04	uint	Texture count

Texture Entry

The MT5 format support external and embedded textures.

Texture ID

Each texture entry has an texture ID which is 8 bytes long.
The actual data type of the ID is still unknown, sometimes it looks like ASCII strings, Shift-JIS or plain garbage.

Position	Length	Type	Description
0x00	0x08	string	Texture ID

TEXN (Texture Entry)

This entry defines an embedded PVRT texture.

Position	Length	Type	Description
0x00	0x08	TextureID	Texture ID
0x08	0x0?	PVRT	Texture

NAME (Texture Names)

This entry defines external PVRT textures each using the texture id for reference.

Position	Length	Type	Description
0x00	0x04	string	Identifier (NAME)
0x04	0x04	uint	Size in bytes
0x08	0x0?	TextureID[]	Texture ID Array

TEXL (Texture Library)

This sections holds offsets to the texture IDs.

Position	Length	Type	Description
0x00	0x04	string	Identifier (TEXL)
0x04	0x04	uint	Size in bytes
0x08	0x04	uint	Texture count

TEXL Entry

Position	Length	Type	Description
0x00	0x04	uint	Offset to TextureID
0x04	0x04	uint	Unknown
0x08	0x04	uint	Unknown

PTRL

This sections holds offsets to various parts of the model.
Its purpose is still unclear.

Position	Length	Type	Description
0x00	0x04	string	Identifier (PTRL)
0x04	0x04	uint	Size in bytes