Collision surfaces

A tree’s collision shape is a CPlugSurfaceGeom: a box, an ellipsoid or a triangle mesh, the mesh stored cooked, with a plane per triangle and an octree over them. Observed · the install’s packs and three TMUnlimiter maps

Chunk 0x0900F004

Order	Field	Type	Confidence
1	Ident	ident	Observed
2	Bounding box	BoxAligned: centre, then half-size (six f32)	Observed
3	Surface kind	i32	Observed
4	The shape	by kind, below	Observed
5	Material ID	i16	Observed

This is the order in the surfaces TMUnlimiter maps embed. Observed · three maps The packs’ 812 surfaces are of surface version 0 and store no surface index; their kinds are 801 meshes, 8 ellipsoids and 3 boxes. Observed · 812 nodes of the packs

Kind	Shape	Confidence
1	Ellipsoid: a vec3	Observed
6	Box: a BoxAligned	Observed
7	Mesh	Observed

The box reads as centre and half-size: in the 77 meshes of three TMUnlimiter maps it equals the vertices’ bounds that way. Observed · 77 meshes

Mesh (version 3)

Order	Field	Type	Confidence
1	Vertices	counted vec3	Observed
2	Triangles	counted 32-byte records: a vec4 plane, three i32 vertex indices, an i16 surface index and two u8	Observed
3	Octree	version 3, counted 32-byte cells	Observed

Observed · the 77 meshes of three maps

In pack files

Reading this chunk in a pack also makes a dummy write of f32(centreX − halfSizeX), little-endian, right after the box: in GBX.NET’s terms the box’s X − X2, its first and fourth floats. Observed · the writes GBX.NET makes over the install’s packs

What are the triangle’s two bytes and the octree’s cells?

The triangle record’s last two bytes and the 32-byte octree cells are read and accounted for; their meaning is not established. Nor is it written down here how the packs’ surface version 0 differs from the order above.