SCHG:Sonic Adventure DX: PC/Model Format

This article is a work in progress. Its content and location may change completely and frequently until this notice is removed.

Remember: all pointers are 4 Bytes, and need to have a key subtracted from them to find the correct location in a file.
For sonic.exe, subtract 0x00400000.
For chrmodels.dll, subtract 0x10000000.
For the dreamcast version, subtract 0x0C900000.

Note: these are listed in the order they will appear in the file. However, it is likely that you will start at the OBJECT Struct.

MESH Struct

The game loads as many of these structs as indicated in the attach struct. The format is as follows.

offset	Type	Description	Notes
0	Byte	Material ID
1	Byte	Poly Type	Always use $C0 (strips)
2	Short	Poly Total	This is how many strips to load
4	Pointer	Polys	Read notes on poly data
8	Padding (0x8)	PNormal and Pattr	Unused by sadx, but are part of official sega model format
10	Pointer	Vertex Colors
14	Pointer	UV Coordinates

VERTEX Struct

A Float[3] for each vertex, times the total specified in the ATTACH Struct.

ATTACH Struct

As a rule, data sets occur in the reverse order that these pointers do. In a non-hacked model, the model data always starts with the material structs and goes down the file to the vertex struct, with the exception of the vertex struct. The verts occur right after the mesh struct and the normals are the last data set before the attach struct. The tools sonic team used strictly followed that rule, but the game can operate outside of that constraint so make sure your pointers are always accurate. A crashing game usually means a bad pointer!

Offset	Type	Description	Notes
0	Pointer	Vertices
4	Pointer	Normals	If this is null, the model doesn't use normals.
8	4 Bytes	Vertex/Normal Total
C	Pointer	Mesh
10	Pointer	Material
14	2 Bytes	Mesh Total
16	2 Bytes	Material Total
18	Float[3]	Center
24	Float	Radius
28	4 Bytes	Null

OBJECT Struct

Offset	Type	Description	Notes
0	4 Bytes	Flags	???
4	Pointer	Attach
8	Float[3]	Position
14	4 Bytes[3]	Rotation	only read first 2 bytes of each
20	Float[3]	Scale
30	Pointer	OBJECT Child
34	Pointer	OBJECT Relate