This tutorial will show you how you can use models (.mdl) for the health/HEV chargers (func_healthcharger/func_recharge), which are normally brush entities. You need to use ZHLT compilers (or its descendants) to properly swap the brush entities' brush models with .mdl files. See the accompanying vault item for models and a sample .rmf using the methods described in this tutorial.

This tutorial requires no custom coding and is intended to work entirely within the confines of vanilla Half-Life's behaviour. Therefore switching skins the usual way or controller bones is out of scope of this tutorial.

The gobbledygook

You can safely skip this section. Go ahead.

We will be exploiting the overlap in the way the engine handles brush models and studio models.

• Brush models are what brush entities normally use. Every compiled bsp file contains one or more brush models, with the first one being the world itself.
• Studio models (so called because Valve used 3D Studio Max) are what point entities normally use e.g. NPCs, weapons, and ammos.

Interestingly in the engine code, the way the engine loads and handles the two have overlaps with regards to the properties. The relevant ones are listed below: As you can see, the way the engine switches texture differs between brush and studio models. With that in mind, we need to prepare our studio model to cater to the way the engine handles brush models. As the health/HEV chargers change the frame value between 0 and 1, the studio model therefore has to be in an animation sequence where at 0/255th of the animation sequence the model shows the ON state, and at 1/255th the OFF state. This translates to using duplicate polygons for the ON/OFF states parented to different bones that moves in the sequence instead of using skin groups.

As for the brush entities, the model keyvalue can be set to point to a .mdl file, but care should be given to ensure it's precached by an earlier entity. Using ZHLT's zhlt_usemodel guarantees this. Also, most (but not all!) brush entities will accept key values intended for studio models (and cycler entity) such as body, sequence, framerate etc. For this tutorial we will be setting our sequence value this way. Most importantly, angles (Pitch Yaw Roll) rotates the entity for func_healthcharger/func_recharge and thus can be used to orient the models properly.

Preparing the model

In order to have the model work for brush entities, it needs to have an animation where the 0/255th of the timeline represents the ON state and 1/255th of the timeline represents the OFF state. For this we need:

• Both ON and OFF state textures (i.e. +0 and +A prefixed textures) as materials.
• 2 or more bones, with 1 being the root bone.
• A duplicate of the faces where the texture changes between the ON and OFF state. The original faces should have the OFF material, and vice versa.
• Faces with the OFF material is parented with the rest of the model to the root bone.
• Faces with the ON material is parented to the second bone.
• At 0/255th of the animation the second bone is positioned so that the ON material is at the front (just 0.1u in front of the rest of the model should work.)
• At 1/255th of the animation the second bone is positioned so that the ON material is at the back and thus the OFF material is visible.

To get the faces to be where it needs to be at the exact fractions of the sequence you can use 2 methods:

• 2-frame animation, where the second frame has the ON material bone position extrapolated (e.g. between 0.1 and -32.0 on the X axis, the bone will be surely be <0.0 at 1/255th of the sequence.)
• 256+ frame animation, where the second frame has the ON material bone positioned safely away from the visible part and remain there for the rest of the animation. Use more frames to be sure.

Other important properties:

• The model should face East (positive towards X axis) when placed in a map with the Yaw value 0, usually using $origin <x> <y> <z> <r=270> QC command.
• The origin of the model and the brush entity should agree. It should be vertically centered as that's where the health/HEV chargers would actually be. Making them flush against the wall facilitates placement in the level.

Optional properties (recommended for versatility, but not required for this tutorial):

• An idle animation with the ON material in front
• ON/OFF skin groups

Using the models in the map

This tutorial supposes that the models you've prepared in the previous section has the following sequences:

• 0: idle (ON faces always visible.)
• 1: onoff (OFF faces visible at exactly 1/255th of the sequence) – we will use this sequence.

Part A: Template entity[ies]

1. Create a monster_furniture or cycler entity for each model you want to use. Give it a name.
2. Set the entity's model to one of the models.
3. Put this entity someplace inaccessible in the map.

Part B: func_healthcharger/ func_recharge entities

1. Create ONLY ONE origin brush (i.e. brush with ORIGIN texture) for each entity. The center of the brush should be flush to the wall, and the vertical center should be 56u above the floor.
2. Tie this brush to entity (func_healthcharger/func_recharge).
3. Set the entity's angles (Pitch Yaw Roll) to face perpendicularly away from the wall.
4. Turn off SmartEdit mode and add the following keyvalues:
   • zhlt_usemodel = <name of template entity>
   • sequence = 1 (index of the sequence as set up earlier)

Part C: Lighting and clipping

• To add clipping, place a CLIP brush with the size of the chargers (usually 32w 48h 8d) where the chargers would've been.
• To have the model take a more fitting lighting (rather than taking the lighting off the floor, see Tutorial: models and lighting for more info), add a small brush textured with black_HIDDEN just below the origin brush from Part B. Tie this brush to a func_detail entity and set "Passable" to Yes. Then add a light entity slightly above this brush and with values 255 255 255 10 (adjust brightness to taste).

Result

See the linked vault item below for sample.

References

• Tutorial: models and lighting
• Entity Programming - Introduction to Entities with Animated Models
• The303 GoldSrc QC reference

Vault