MDL (GoldSrc)

Quake

GoldSrc

Source Engine

Source 2

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MDL (sometimes referred to as Half-Life MDL or HLMDL) is a model format used by GoldSrc to store dynamically lit models which can be animated using skeletal animation, along with their associated textures. It is a heavily modified version of the Quake MDL format.

Overview

Limits

HLMDL has the following limits per input SMD:

• 1 mesh
  • 2048 vertices (and vertex normals) per mesh
  • 4080 triangles per mesh
• 1 animation sequence
  • 512 keyframes per sequence
• 128 bones

Additionally, the following limits apply to the whole MDL:

• 4 bone attachments
• 8 bone controllers
• 32 meshes across all submodels
• 256 animation sequences.

Textures must:

• Be 8-bit uncompressed BMP files.
• Have a resolution which is a multiple of 8 (multiples of 16 are preferred).
• Have a resolution which does not exceed 512x512 (soft limit; raised to 1024x1024 in Sven Co-op and other engines like FTE).
• Have a file name which is not longer than 64 characters (including the .bmp extension).

Important:Older versions of StudioMDL, including the version found in the Half-Life SDK on Steam, do not support tiling UVs, clamping them to the edge of the texture. This is not a limitation of the HLMDL file format; the Sven Co-op StudioMDL can create MDLs compatible with vanilla GoldSrc which have tiled UVs.

Bug:The latest version of the Sven Co-op StudioMDL (from December 2020), as found in the Sven Co-op SDK, has some bugs with bounding boxes; use the version linked above instead (from November 2018).  [todo tested in ?]

Tip:To create a model or submodel with more than 4080 tris, split the model into multiple SMD meshes, with a separate $body or $bodygroup entry for each mesh in the QC file.

Warning:Avoid going over 9000 tris!
While the HLMDL format can handle over 100K tris, the old OpenGL renderer struggles with such "high-poly" models, even on high-end GPUs.^[1]

Note:Third party games that upgrade the renderer (ex: , or ) can handle higher polygon MDLs better. This does not include Sven Co-op, which uses a mostly vanilla renderer.
This is obviously not a problem for games on engines much newer than GoldSrc that use the HLMDL format, such as Codename: Loop () or FreeCS ().

Confirm:Is this soft limit 9000 total, or 9000 being displayed simultaneously?

Confirm:Can custom renderers without engine access, such as Trinity Engine, improve performance for higher-poly MDLs?

Code:While MDL does not natively support animated textures, a model's skin can be quickly switched between in game code to animate between them. For example, monster_houndeye uses skin switching to blink.

Confirm:Max textures, max skins, and other limits?

Flags

Model flags

Particle effects cannot be combined, but all others can.^[Clarify]

Bit	Flag name	Particle effect?	Description
1	EF_ROCKET	Yes	Quake I rocket trail particles and dynamic light
2	EF_GRENADE	Yes	Quake I grenade trail smoke particles
4	EF_GIB	Yes	Quake I gib blood trail particles
8	EF_ROTATE	No	Rotate this model around its origin, like the weapon pickups in Quake I; requires supported game code.
16	EF_TRACER	Yes	Quake I skrag spit particles
32	EF_ZOMGIB	Yes	Quake I zombie blood; like EF_GIB, but darker
64	EF_TRACER2	Yes	Quake I death knight slashing particles
128	EF_TRACER3	Yes	Like EF_GRENADE, but only has one trail
256	EF_NOSHADELIGHT	No	Reduces intensity of shadows on the model, without making the model flat Confirm:Half Lambert?
512	EF_HITBOXCOLLISIONS	No	Use hitbox for collision instead of bounding box
1024	EF_FORCESKYLIGHT	No	Always use skybox lighting, regardless of model location

Texture flags

Bit	Flag name	Description
1	STUDIO_NF_FLATSHADE	Shade the model a single tint, without any shadowing, resulting in the model looking "flat" like a cartoon character.
2	STUDIO_NF_CHROME	Use matcap environment mapping to render the texture as a sphere map. Bug:Limited to 64x64 in vanilla GoldSrc; this is fixed in Sven Co-op. Chrome resolutions higher than 256x256 tend to have diminishing returns.  [todo tested in ?] Note:Automatically set for any textures that contain the string chrome somewhere in their name. Important:Setting the chrome flag via StudioMDL will also add the flatshade flag, as well as move all UV coordinates to the top-left corner (chrome doesn't use UV mapping).
4	STUDIO_NF_FULLBRIGHT	Display texture at maximum brightness, ignoring lighting. Bug:Doesn't work in vanilla GoldSrc; fixed in Sven Co-op and custom renderers.  [todo tested in ?]
8	STUDIO_NF_MIPMAPS	Generates mipmaps for the texture, greatly reducing texture aliasing at a distance. No effect in Sven Co-op, which always generates mipmaps for models, regardless of this flag. Bug:This flag was actually originally intended to disable mipmaps for a texture, but this behavior was accidentally inverted. Confirm:Allegedy fixed in 25th Anniversary Update.   [todo tested in ?] Tip:Recommended for most textures except alphatested ones. Due to the way textures are stored, enabling mipmaps of alphatested texture will result in the texture transparency becoming more exaggerated at a distance, with fine details like thin foliage and wire fences disappearing, and shadowing occurring around the edges occurring due to transparent texels not being dilated.
16	STUDIO_NF_ALPHA	Unused?
32	STUDIO_NF_ADDITIVE	Use additive translucency. Still affected by entity lighting; use the Additive rendermode on an entity to ignore lighting. Bug:Sometimes breaks normals of non-additive faces on the same mesh. Workaround:Split the additive portions onto a different mesh, by listing it as a separate SMD with a separate $body line (usually after the main mesh). Tip:This affects the order in which faces are loaded into the z-buffer, which can be used for manual alpha sorting. In practice, this means defining an additive chrome overlay (to simulate specular highlights) as a separate mesh after the main mesh will prevent  z-fighting, even if the mesh is coplanar.   [todo tested in ?]
64	STUDIO_NF_MASKED	Use binary alphatest transparency, wherein the last palette entry of the texture is transparent.

In other engines

Half-Life MDLs are supported by FTE and the Unity game Codename: Loop.

External links

• The303's GoldSrc model tutorials and documentation
• Assimp documentation for HLMDL

References

1. From the GoldSrc Model Export Tutorial by The303:
   In order to compile models with more than 4080 triangles, you must break up your SMD's into parts and give them their own $body lines for compiling. Also, FOR THE LOVE OF ALL THAT IS HOLY PLEASE DO NOT GO CRAZY ON YOUR TRIANGLE COUNT; remember this is goldsrc, not source engine. Going any higher than 9000 tris is excessive and direct ports from source/other games are inefficent, wasteful, and cause performance issues for the old renderer.

   — The303