SM64DS BMD (3D model) format documentation -- by Mega-Mario

0. File header
It is 60 bytes long and laid out as such:
Offset	Size	Desc.
0x00	4		Scale factor (0=normal, 1=2x bigger, 2=4x bigger...)
0x04	4		Number of bones
0x08	4		Offset to bones section
0x0C	4		Number of display lists
0x10	4		Offset to display lists section
0x14	4		Number of textures
0x18	4		Offset to textures section
0x1C	4		Number of texture palettes
0x20	4		Offset to texture palettes section
0x24	4		Number of materials
0x28	4		Offset to materials section
0x2C	4		Offset to transform/bone map
0x38	4		Seems to be the offset of the texture/palette data block

1. Bones section
The bones map display lists (geometry) to transforms and materials. Each bone entry is 64 bytes long and laid out as such:
Offset	Size	Desc.
0x00	4		Bone ID (usually assigned incrementally from zero)
0x04	4		Offset to bone name (null-terminated ASCII string)
0x08	2		Offset in bones to parent bone (signed 16-bit. 0=no parent, -1=parent is the previous bone, ...)
0x0A	2		1 if the bone has children, 0 otherwise
0x0C	4		Offset in bones to the next sibling bone (0=bone is last child of its parent)
0x10	4		X scale (32-bit signed, 20:12 fixed point. Think GX command 0x1B)
0x14	4		Y scale
0x18	4		Z scale
0x1C	2		X rotation (16-bit signed, 0x0400 = 90°)
0x1E	2		Y rotation
0x20	2		Z rotation
0x22	2		Zero (padding)
0x24	4		X translation (32-bit signed, 20:12 fixed point. Think GX command 0x1C)
0x28	4		Y translation
0x2C	4		Z translation
0x30	4		Number of displaylist/material pairs
0x34	4		Offset to material IDs list
0x38	4		Offset to displaylist IDs list
0x3C	4		Bit0: bone is rendered facing the camera (billboard); Bit2: ???

Transforms are applied in SRT order (scale first, then rotation and translation).
Each bone's transforms are used to build a 4x4 transform matrix.
Each bone's transform matrix is multiplied with its parent's transform matrix.

The material and displaylist IDs lists are series of bytes, one for each pair.


2. Display lists section
First, there's a list of offsets. Each entry is 8 bytes long.
Offset	Size	Desc.
0x00	4		??? (usually 1)
0x04	4		Offset to the display list

The display list consists into a 16-byte header:
Offset	Size	Desc
0x00	4		Number of transforms
0x04	4		Offset to transforms list
0x08	4		Size of the display list data in bytes
0x0C	4		Offset to the display list data

The display list data is a packed GX display list. It is directly copied to the GXFIFO when rendering on a DS.

The transforms list is a series of bytes.
Every time a Matrix restore (0x14) command is issued by the display list, the command's parameter (the matrix ID)
is used as an index into the transforms list. The ID obtained from the transforms list is then used as an index into
the transform/bone map (series of shorts whose offset is defined in the file header, at 0x2C). The ID finally obtained
is the ID of the bone whose transform matrix will be used to transform oncoming geometry.


3. Textures section
Each texture entry is 20 bytes long and laid out as such:
Offset	Size	Desc.
0x00	4		Offset to texture name (null-terminated ASCII string)
0x04	4		Offset to texture data
0x08	4		Size of the texture data in bytes
0x0C	2		Texture width
0x0E	2		Texture height
0x10	4		Texture parameters (think GX command 0x2A) (part 1, tells texture size and type)

The IDs of texture entries are assigned incrementally from zero.

For compressed (type 5) textures, the size of the texture data doesn't count the palette index data.
The texture data is then directly followed by (size/2) of palette index data.


4. Texture palettes section
Each texture palette entry is 16 bytes long and laid out as such:
Offset	Size	Desc.
0x00	4		Offset to palette name (null-terminated ASCII string)
0x04	4		Offset to palette data
0x08	4		Size of the palette data in bytes
0x0C	4		??? (usually 0xFFFFFFFF)

The IDs of palette entries are assigned incrementally from zero.

The palette data is 15-bit BGR color.


5. Materials section
Materials tell the texture, colors and other attributes to use for each piece of geometry in the model.
Each material entry is 48 bytes long and laid out as such:
Offset	Size	Desc.
0x00	4		Offset to material name (null-terminated ASCII string)
0x04	4		Texture ID (0xFFFFFFFF = no texture)
0x08	4		Texture palette ID (0xFFFFFFFF = no palette)
0x0C	4		Texture S scale (32-bit signed, 20:12 fixed point)
0x10	4		Texture T scale
0x14	2		Texture rotation (16-bit signed, 0x0400 = 90°)
0x18	4		Texture S translation (32-bit signed, 20:12 fixed point)
0x1C	4		Texture T translation
0x20	4		Texture paramters (think GX command 0x2A) (part 2, tells how to apply the texture)
0x24	4		Polygon attributes (think GX command 0x29)
0x28	4		Diffuse/ambient parameters (think GX command 0x30)
0x2C	4		Specular/emission parameters (think GX command 0x31)

The Texture parameters value found in a material entry holds the texture repeat and transform bits. It is ORed with the
Texture parameters value found in the texture entry (and other stuff) to form the full Texture parameters value.
Texture transforms are applied in SRT order. They only work if the Texture parameters value indicates a texture transform
mode different from zero.

A material entry may have a texture assigned but no palette, if the texture is a direct color texture (type 7).


Refer to GBAtek for more information about the GX commands and how the DS' GX hardware works.