MDL

MDL is the extension for Source's proprietary model format. It defines the structure of the model along with animation, bounding box, hit box, material, mesh and LOD information. It does not, however, contain all the information needed for the model. Additional data is stored in PHY, ANI, VTX and VVD files, and sometimes, usually for shared animations, other .mdl files.

File format

Some details of the file format may be gleaned from the source code in Valve's studio.h, specifically the struct studiohdr_t. The early header defines a series of offsets and lengths for various sub-sections within the file, along with some key scalar information. The MDL also contains the names of materials (VMT) which are used as the numerically-defined swappable skins.

Main header

struct studiohdr_t
{
	int		id;		// Model format ID, such as "IDST" (0x49 0x44 0x53 0x54)
	int		version;	// Format version number, such as 48 (0x30,0x00,0x00,0x00)
	char[64]	name;		// The internal name of the model, padding with null bytes.
					// Typically "my_model.mdl" will have an internal name of "my_model"
	int		dataLength;	// ??
 
	// A vector is 12 bytes, three 4-byte float-values in a row.
	Vector		eyeposition;	// Position of player viewpoint relative to model origin
	Vector		illumposition;	// ?? Presumably the point used for lighting when per-vertex lighting is not enabled.
	Vector		hull_min;	// Corner of model hull box with the least X/Y/Z values
	Vector		hull_max;	// Opposite corner of model hull box
	Vector	  	view_bbmin;
	Vector	 	view_bbmax;
 
	int		flags;		// ??
 
	/*
	 * After this point, the header contains many references to offsets
	 * within the MDL file and the number of items at those offsets.
	 *
	 * Offsets are from the very beginning of the file.
	 * 
	 * Note that indexes/counts are not always paired and ordered consistently.
	 */	
 
	// mstudiobone_t
	int		bone_count;	// Number of data sections (of type mstudiobone_t)
	int		bone_offset;	// Offset of first data section
 
	// mstudiobonecontroller_t
	int		bonecontroller_count;
	int		bonecontroller_offset;
 
	// mstudiohitboxset_t
	int		hitbox_count;
	int		hitbox_offset;
 
	// mstudioanimdesc_t
	int		localanim_count;
	int		localanim_offset;
 
	// mstudioseqdesc_t
	int		localseq_count;
	int		localseq_offset;
 
	int		activitylistversion; // ??
	int		eventsindexed;	// ??
 
	// VMT texture filenames
	// (A series of null-terminated strings)
	int		texture_count;
	int		texture_offset;
 
	// Relative paths to search for textures
	// (A series of null-terminated strings)
	int		texturedir_count;
	int		texturedir_offset;
 
	// Skin family information for replaceable textures
	int		skinreference_count;
	int		skinrfamily_count;
	int             skinreference_index;
 
	// mstudiobodyparts_t
	int		bodypart_count;
	int		bodypart_offset;
 
        // Local attachment points		
	// mstudioattachment_t
	int		attachment_count;
	int		attachment_offset;
 
	// Node values appear to be single bytes, while their names are null-terminated strings.
	int		localnode_count;
	int		localnode_index;
	int		localnode_name_index;
 
	// mstudioflexdesc_t
	int		flexdesc_count;
	int		flexdesc_index;
 
	// mstudioflexcontroller_t
	int		flexcontroller_count;
	int		flexcontroller_index;
 
	// mstudioflexrule_t
	int		flexrules_count;
	int		flexrules_index;
 
	// IK probably referse to inverse kinematics
	// mstudioikchain_t
	int		ikchain_count;
	int		ikchain_index;
 
	// Information about any "mouth" on the model for speech animation
	// More than one sounds pretty creepy.
	// mstudiomouth_t
	int		mouths_count; 
	int		mouths_index;
 
	// mstudioposeparamdesc_t
	int		localposeparam_count;
	int		localposeparam_index;
 
	/*
	 * For anyone trying to follow along, as of this writing,
	 * the next "surfaceprop_index" value is at position 0x0134 (308)
	 * from the start of the file.
	 */
 
	// Surface property value (single null-terminated string)
	int		surfaceprop_index;
 
	// Unusual: In this one index comes first, then count.
	// Key-value data is a series of strings. If you can't find
	// what you're interested in, check the associated PHY file as well.
	int		keyvalue_index;
	int		keyvalue_count;	
 
	// More inverse-kinematics
	// mstudioiklock_t
	int		iklock_count;
	int		iklock_index;
 
 
	float		mass; 		// Mass of object (4-bytes)
	int		contents;	// ??
 
	// Other models can be referenced for re-used sequences and animations
	// (See also: The $includemodel QC option.)
	// mstudiomodelgroup_t
	int		includemodel_count;
	int		includemodel_index
	
	int		virtualModel;	// Placeholder for mutable-void*
 
	// mstudioanimblock_t
	int		animblocks_name_index;
	int		animblocks_count;
	int		animblocks_index;
	
	int		animblockModel; // Placeholder for mutable-void*

	// Points to a series of bytes?
	int		bonetablename_index;
	
	int		vertex_base;	// Placeholder for void*
	int		offset_base;	// Placeholder for void*
	
	// Used with $constantdirectionallight from the QC 
	// Model should have flag #13 set if enabled
	byte		directionaldotproduct;
	
	byte		rootLod;	// Preferred rather than clamped
	
	// 0 means any allowed, N means Lod 0 -> (N-1)
	byte		numAllowedRootLods;	
	
	byte		unused; // ??
	int		unused; // ??
	
	// mstudioflexcontrollerui_t
	int		flexcontrollerui_count;
	int		flexcontrollerui_index;
}

Todo: This header information is incomplete.

See also

• Model Viewer
• Model Creation Overview
• Model