SCHG:Sonic Jam/Models

SCHG: Sonic Jam
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Model data starts at $3F908 in MUSEUM.MUS.

Model Format

Models generally consist of the following parts. There are some exceptions, but the general order stays the same.

Vertices

The first part are vertices, stored as a 3D vector.

Indexing Table

The second part is the indexing table for quads, using the vertices given. Indices are words, and jump by $08. The first vertex would be $0000; the second would be $0008. There's one for each quad.

Vertex Normals

The third, for objects that use Dynamic Gouraud Shading, are the vertex normals. These are normalized 3D vectors. As you'd expect, there's one for each vertex.

Draw Settings

After the above is the draw settings. There's one list of settings for each quad. Each list is 16 bytes long. Here's its format:

Description	Length
Unknown. Highest bit seems to turn off backface culling.	Byte
Unknown. Bits $1 and $2 affect depth testing in certain instances.	Byte
Texture index. $0-$1DB.	Word
CMDPMOD command for VDP1. Bit flags.	Word
Unknown.	Word
Static/Dynamic Gouraud Shading Table Index.	Word
CMDCTRL command for VDP1. Bit flags.	Word
Unknown.	Word
Unknown.	Word

Footer

This can vary from model to model, depending on which parts are present. For Sonic, this consists of the following:

1. Pointer to start of vertices (long), number of vertices (long)
2. Pointer to start of indexing table (long), number of quads (long)
3. Pointer to draw command (long)
4. Pointer to vertex normals (long)

Model Groups

Some models, such as Sonic and Tails, consist of multiple models in a group. After the last model in the group, there's a footer.

The first part of the footer is a list of addresses pointing to each model's footer.

The second part is a list of 3D Vectors, relative positions for each model. They correspond to the addresses given in the previous section.

Certain model groups have some seemingly unused data that appears before the footer. This data seems to correlate with how the model group parenting hierarchy is set up.

Model List

Here's the list of models in the game that are currently known. Addresses given are pointers to footers, for both model groups and individual models.

Name	Address

Sonic	$42620
Body	$40058
Head	$40C58
Right Thigh	$40DA8
Right Calf	$41048
Right Foot	$412A0
Left Thigh	$413F0
Left Calf	$41690
Left Foot	$418E8
Right Bicep	$41A50
Right Forearm	$41CF0
Right Hand	$41F18
Left Bicep	$42080
Left Forearm	$42320
Left Hand	$42548
Tail	$42608