VTX
VTX is the extension for Source's proprietary mesh strip format. It stores hardware optimized material, skinning and triangle strip/fan information for each LOD of each mesh in the MDL.
It is currently found in .sw.vtx (Software), .dx80.vtx (DirectX 8.0) .dx90.vtx (DirectX 9.0) and .xbox.vtx (XBox) flavors. Left 4 Dead and Left 4 Dead 2 originally used just .VTX files, as of the Sacrifice update for these two games they now use the .dx90.vtx for the Mac OSX and re-used the .VTX only for Portal 2.
File Structure
Header
// this structure is in <mod folder>/src/public/optimize.h
struct FileHeader_t
{
// file version as defined by OPTIMIZED_MODEL_FILE_VERSION (currently 7)
int version;
// hardware params that affect how the model is to be optimized.
int vertCacheSize;
unsigned short maxBonesPerStrip;
unsigned short maxBonesPerTri;
int maxBonesPerVert;
// must match checkSum in the .mdl
int checkSum;
int numLODs; // Also specified in ModelHeader_t's and should match
// Offset to materialReplacementList Array. one of these for each LOD, 8 in total
int materialReplacementListOffset;
//Defines the size and location of the body part array
int numBodyParts;
int bodyPartOffset;
};
This is the header structure for the current VERSION7 .vtx file
Body array
The body array is a list of BodyPartHeader_t objects.
Size is specified by: numBodyParts.
Location is specified by bodyPartOffset. This is relative to the header, which is alwasy 0x0 and can therefore the offset can allways be treated as a static address.
BodyPartHeader_t
struct BodyPartHeader_t
{
//Model array
int numModels;
int modelOffset;
};
Model array
The model array is a list of ModelHeader_t objects.
Size is specified by: numModels.
Location is specified by bodyPartOffset. This is a relative offset, from the start of the BodyPartHeader_t object.
ModelHeader_t
// This maps one to one with models in the mdl file.
struct ModelHeader_t
{
//LOD mesh array
int numLODs; //This is also specified in FileHeader_t
int lodOffset;
};
LOD Mesh Array
The LOD mesh array is a list of ModelLODHeader_t objects.
Size is specified by: numLODS
Location is specified by lodOffset. This is again a relative offset, from the start of the Modelheader_t object.
ModelLODHeader_t
struct ModelLODHeader_t
{
//Mesh array
int numMeshes;
int meshOffset;
float switchPoint;
};
Mesh array
The mesh array is a list of MeshHeader_t objects.
Size is specified by: numMeshes.
Location is specified by meshOffset. Relative offset from the start of the ModelLODHeader_t object.
Switch Point
The point at which the engine should switch to this LOD mesh is defined by switchPoint.
MeshHeader_t
struct MeshHeader_t
{
int numStripGroups;
int stripGroupHeaderOffset;
unsigned char flags;
};
Strip Group Array
The strip group array is a list of StripHeader_t objects.
Size is specified by: numStripGroups
Location is specified by stripGroupHeaderOffset. Relative from MeshHeader_t object.
Flags
The unsigned char flags value can be read from this table:
| Value | Meaning |
|---|---|
| 0x01 | STRIPGROUP_IS_FLEXED |
| 0x02 | STRIPGROUP_IS_HWSKINNED |
| 0x04 | STRIPGROUP_IS_DELTA_FLEXED |
| 0x08 | STRIPGROUP_SUPPRESS_HW_MORPH |
StripHeader_t
// A strip is a piece of a stripgroup which is divided by bones
struct StripHeader_t
{
//Indices array
int numIndices;
int indexOffset;
//Vertices array
int numVerts;
int vertOffset;
short numBones;
unsigned char flags;
int numBoneStateChanges;
int boneStateChangeOffset;
};
Indices array
The indices array is a list of unsigned short indices.
Size is specified by: numIndices.
Location is specified by indexOffset. Relative from StripHeader_t object.
Vertices array
The vertex array is a list of Vertex_t objects.
Size is specified by: numVerts.
Location is specified by vertOffset. Relative from StripHeader_t object.
Vertex_t
struct Vertex_t
{
// these index into the mesh's vert[origMeshVertID]'s bones
unsigned char boneWeightIndex[3];
unsigned char numBones;
unsigned short origMeshVertID;
// for sw skinned verts, these are indices into the global list of bones
// for hw skinned verts, these are hardware bone indices
char boneID[3];
};
origMeshVertID defines the index of this vertex that is to be read from the linked .VVD file's vertex array