Procedural Skeleton Generation in Houdini — Rig Bones Generator
- Pavel Zosim
- Jan 25
- 3 min read
Updated: Jan 26
A procedural Houdini tool for fast skeleton generation, consistent joint naming, and reusable rig presets. Designed for game-ready skeletons, Apex workflows, and batch animation export.
Procedural Skeleton Workflow in Houdini
When creating skeletons in Houdini, a large part of the work is repetitive. Each joint must be positioned manually, named according to convention, mirrored for symmetry, and connected into a hierarchy. This process is repeated for every new model and quickly becomes time-consuming.
To address this, I developed rig_bones_generator — a procedural skeleton generation system for Houdini. The goal of the tool is to reduce iteration cost and allow reusable skeleton presets for anatomically similar assets, such as humanoid characters or vehicles with symmetric structure.
The system focuses on three core problems: automatic joint naming based on game industry conventions, working with different types of topology, and preparing skeletons for downstream workflows such as Apex rigging or animation export.
Skeleton Creation Workflow
The first stage is skeleton creation, which includes joint positioning and naming.
For clean and predictable topology, joint placement is driven by edge selection. In this mode, the algorithm places joints precisely in the center of the selected area, helping to maintain correct deformation and weight distribution.
For broken topology or quick concept meshes, point selection is used instead.
By selecting point groups — including points behind the visible surface — joints can be placed reliably even on remeshed or unstable geometry.
Joint naming is handled automatically.
The naming format follows a standard structure: joint type, body region, side, and index. The user only needs to specify the bone name and enable the required options.
For symmetrical bones, selecting left or right automatically applies side suffixes and generates mirrored joints. For chains such as the spine or tails, indexed naming can be enabled to generate numbered joints automatically.
Additional joints can be inserted by defining start and end joints and applying resampling. This creates intermediate joints for finer rotational control. Joint orientation can also be adjusted when needed, although for models aligned to the +Z axis, default settings are usually sufficient.
Hierarchy and Parenting
Once joint positions and names are defined, the skeleton hierarchy is created using the parenting workflow. Parent and child joints are assigned in the parent joint tab.
To speed up this process, wildcard patterns can be used in joint names. This allows entire mirrored joint groups to be connected to a parent in a single operation, avoiding repetitive manual connections.
At this stage, the skeleton is already suitable for export to a game engine.
Apex Integration
For more advanced rigs, the skeleton can be extended using Apex, Houdini’s procedural rig-graph system. Apex operates on top of an existing skeleton and uses tags to build rig logic.
The rig_bones_generator node outputs three data streams:
Skeleton — joint hierarchy
Guides — tagged data for Apex
Weights — bone influence weights
All three outputs are connected to a standard Apex setup, allowing the construction of modular IK/FK rigs without modifying the underlying skeleton.
FBX Export and Animation Retargeting
For export, the ROP FBX Character Output node is used. Connecting the skeleton and weights outputs is sufficient to export a game-ready FBX file.
Animation retargeting is handled using Houdini’s MapPoints workflow. As long as bone names remain consistent, animations from external sources — such as Mixamo — can be mapped and reused.
Using a TOP network, multiple animation clips can be baked and exported into a single FBX file. This allows batch processing and keeps all required animations in one asset. Testing in Unity confirms that clip names and animations are preserved correctly.
Preset-Based Workflow
Once configured, the rig_bones_generator node becomes a reusable preset. It can be duplicated across different models, where only joint positions need to be reassigned. Naming, hierarchy, mirroring, and connections are handled automatically.
A single preset can be created for human anatomy, but the same approach can be used for any type of asset requiring consistent skeletal structure.
Conclusion
rig_bones_generator is designed to reduce repetitive rigging work and enforce consistent structure across assets. By separating skeleton generation from higher-level rig logic, the system supports scalable production workflows for games and real-time applications.
Links
Apex rig and animation retargeting examples follow standard Houdini workflows.
Additional references used during development:
Download Procedural Skeleton Generator for Houdini:
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