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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


// 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: numBodyParts.
  • Location: bodyPartOffset.
Note.png Note: Since this value is in the header it can be interpreted as an absolute location


struct BodyPartHeader_t
	//Model array
	int numModels;
	int modelOffset;

Model array

The model array is a list of ModelHeader_t objects.

  • Size: numModels.
  • Location: bodyPartOffset.


// 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: numLODS.
  • Location: lodOffset.


struct ModelLODHeader_t
    //Mesh array
	int numMeshes;
	int meshOffset;

	float switchPoint;

Mesh array

The mesh array is a list of MeshHeader_t objects.

  • Size: numMeshes.
  • Location: meshOffset.

Switch Point

The point at which the engine should switch to this LOD mesh is defined by switchPoint.


struct MeshHeader_t
	int numStripGroups;
	int stripGroupHeaderOffset;

	unsigned char flags;

Strip Group Array

The strip group array is a list of StripGroupHeader_t objects.

  • Size: numStripGroups.
  • Location: stripGroupHeaderOffset.


The unsigned char flags value can be read from this table:

Value Meaning


struct StripGroupHeader_t
	// These are the arrays of all verts and indices for this mesh.  strips index into this.
	int numVerts;
	int vertOffset;

	int numIndices;
	int indexOffset;

	int numStrips;
	int stripOffset;

	unsigned char flags;

	//if you have problems with parsing try to skip 8 bytes here

Vertex & Indices arrays

Indices Array - This is a set of unsigned short integers that index the position of the real vertex data in the .VVD's vertex array

  • Size: numIndices
  • Location: indexOffset

Vertex Array - The vertex array inside the .VTX file holds some extra information related to skinning

  • Size: numVerts
  • Location: vertOffset

Strip Array

The strip array is a list of StripHeader_T objects

  • Size: numStrips
  • Location: stripOffset


// A strip is a piece of a stripgroup which is divided by bones 
struct StripHeader_t
	int numIndices;
	int indexOffset;

	int numVerts;    
	int vertOffset;

	short numBones;

	unsigned char flags;

	int numBoneStateChanges;
	int boneStateChangeOffset;

Indices & Vertex Groupings

Each group (Indices and Vertexes respectively), specify what position to read from the vertex pool, as well as the indices pool. These pools come from the parent StripGroupHeader object


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

Note.png Note: This value needs to be added to the total vertices read, since it is relative to the mesh and won't work as an absolute key.

See also