The Gearbox model tag contains the marker points and render models for objects such as vehicles, scenery, and weapons among others. It is not collideable nor animated on its own, and objects may reference additional model_collision_geometry and model_animations tags. This tag supports LODs and permutations, and includes shader_model references.

Don't confuse this tag with the Xbox-only model, which Gearbox modified for the PC port. It is therefore used in all derivatives of that port, like Mac, Demo, and MCC. Unlike the Xbox version, the Gearbox model uses uncompressed vertices.

Shaders

Each part of a model can reference a different shader, like the Warthog's windscreen using a shader_transparent_glass while its body uses a shader_model. While a model can technically reference any kind of shader, referencing a shader_environment (used for BSPs) is not recommended because it renders incorrectly in Custom Edition.

Markers

Markers are simple named points with orientation attached to a model. Since they are parented by nodes, they can be animated. Markers can be used for a variety of purposes, such as attaching objects together with scripts (e.g. Pelicans carrying Warthogs), attaching widgets like antenna, or firing projectiles from in the case of weapons.

This tag only contains the marker data but other tags usually determine how they are used. However, certain marker names have special behaviour in-engine:

• head:
  • Determines where AI look at when scripted to talk to another character.
  • Base location for the friendly indicator in multiplayer.
  • Used as a ray origin when testing if AI can see their enemy.
• primary trigger: Where a weapon's primary trigger projectiles and effects come from. See also the projectiles use weapon origin field.
• secondary trigger: As above, for secondary triggers (second trigger slot).
• body
• front: Possibly used to used to see if you're facing a device_control, if present.
• ground point: Determines the resting point for items.
• left hand: Used during the grenade throwing animation.
• melee: Where melee damage comes from here. If not present, the engine picks an unknown default location.
• hover thrusters:
  • When used on a vehicle with "alien scout" or "alien fighter" vehicle physics type, creates a dust cloud effect when the vehicle is hovering close to the ground. This can be seen at a piloted Banshee's wingtips when sitting on the ground.
  • When the vehicle physics type is "human plane", creates a similar dust effect if the marker is pointed at nearby ground. Used for the Pelican's thrusters.
• jet thrusters: Can also be used for vehicles with "human plane" physics to create the Pelican's thruster dust effect.

Tool only includes markers from the superhigh LOD.

Regions

Regions are named sections of the model which can have multiple permutations. Region names are used by the engine to relate parts of the render model with the collision model. For example, a Flood combat form losing an arm. Some regions have special behaviour in-engine:

• head: Sets headshot areas for damage_effect.

Regions render in the order they are stored in the tag. When naming regions, consider that they will be sorted by name when compiled into the .gbxmodel. This can be important for skyboxes and objects with multiple layers of alpha-blended transparent shaders which aren't z-culled and need a correct sorting order to be explicitly defined, assuming the object is viewed mostly from one direction.

Permutations

A permutation is a randomly selected variation of a region. They are often used to give bipeds visual variety. Some permutations have special behaviour in-engine:

• ~blur: Switched to depending on weapon rate of fire and vehicle speed to fake motion blur. Used for the Warthog tires and chaingun when spinning fast enough.

Permutations are not network synchronized.

Level of detail

Models can contain multiple levels of detail (LODs) which are rendered for the object depending on its on-screen size. An object which is very distant and small does not need a lot of geometric detail, so it can be rendered using a simplified mesh with fewer or simpler shaders in order to keep framerates high in busy scenes.

Halo CE supports 5 LODs whose pixel cutoffs can be configured in this tag. From best to worst quality:

• super high
• high
• medium
• low
• super low

When rendering first person models, Halo always uses the lowest quality LOD instead of the highest. When creating FP arms or weapons create a separate FP model from your 3P model which only includes a single super high LOD.

LODs are created by using a special naming convention when compiling models with Tool.

Structure and fields

This information was partially generated using Invader tag definitions.

Acknowledgements

Thanks to the following individuals for their research or contributions to this topic:

• Fubih (Regions render order tip)
• Kavawuvi (Invader tag definitions)
• MosesOfEgypt (Tag structure research)