Houkit

A utility for procedural modeling with the Houdini Object Model (HOM). Houkit is built for Python SOP workflows: use Python for the modeling logic, and use the SOP network to inspect every stage of the result.

It suits programming-oriented, precision, math-driven, and procedural modeling. A SOP stage can be displayed or bypassed while you inspect points, topology, attributes, warnings, and intermediate geometry in Houdini.

Features

• Turn module-level Python functions into Python SOPs. Build a network in code without losing Houdini’s normal debugging workflow.

  extruded = sopify(subnet, head.indirectInputs()[0], _extrude_lips)
  add_output(head, "OUT_HEAD", extruded)

• Use attributes as stable point references. Complex models outgrow point-number references. Name a point leg_2_joint, retrieve it later, and retain that relationship while topology changes.

  p0, p1, p2 = points_from_geo(geo, "id", "a", "b", "c")

• Reload changed Python modules from Houdini. This shortens the edit-and-test loop without restarting Houdini or regenerating the HIP file. Regenerate when the SOP network or its parameter interface changes.

  head = add_reloadable_subnet(parent, "head")

Topology helpers include inset, outset, extrusion, quad-based pentagon fills, loop cuts, point merging, point splitting, and normal recalculation. Attribute and group data is preserved where operations rebuild geometry.

inset_result = inset(prims, scalar=1, use_ratio=False, follow_existing_edge=True)

For SOP interfaces, Houkit adds reloadable subnets, common built-in SOPs such as Mirror, Fuse, and Output, parameter folders and headings, and promoted controls.

leg = add_reloadable_subnet(parent, "leg")
add_float_parm(leg, "length")
length = get_parms(leg).length

For the complete API and type signatures, inspect the façade source files.

Setup

Set Houdini’s hython executable as the project interpreter. Houkit is tested with Houdini 22.0.368 and its Python 3.11 build; no additional packages are required because Houdini includes NumPy.

Add Houkit as a top-level submodule:

git submodule add https://github.com/red-bean-pasta/houkit houkit

Make the submodule root importable in the Houdini project, then use the public façade modules—for example, houkit.topology.inset rather than houkit.topologies.face_offseter.inset. The façades are the stable interface; internal modules may be refactored.

Main modules

• topology — topology creation, editing, adjacency, and spatial helpers.
• attributer — create, query, positionally name, deduplicate, and transfer attributes.
• noder — build SOP networks, generate Python SOPs, create reload controls, and add common nodes such as merge, fuse, mirror, and output.
• parameterizer — add parameters, read parameter values, and promote child-network controls.
• geomath — vector and line operations, rotations, and conic or elliptical interpolation for geometry algorithms.
• grouper, formatter, and developing — small helpers for geometry groups, naming, saving, and module reloads.

Example

This Python SOP creates a named quad, extrudes it, then retrieves and moves one point by its semantic identifier. In a larger network, keep stages this small so every SOP remains easy to inspect.

import hou
from hou import Vector3

from houkit.topology import add_point, fill_face, extrude, offset_point
from houkit.attributer import add_point_attrib, points_from_geo


geo = hou.pwd().geometry()

add_point_attrib(geo, "id", "")

points = [
    add_point(geo, Vector3(0, 0, 0), ("id", "corner_1")),
    add_point(geo, Vector3(1, 0, 0), ("id", "corner_2")),
    add_point(geo, Vector3(1, 1, 0), ("id", "corner_3")),
    add_point(geo, Vector3(0, 1, 0), ("id", "corner_4")),
]
face = fill_face(points)
extrude(face, 0.25)

corner_1, = points_from_geo(geo, "id", "corner_1")
offset_point(corner_1, Vector3(-1, 0, 0))

More examples

Houdini Spider Generator is a complete procedural-modeling project built with Houkit.

Acknowledgements

This project is manually directed, reviewed, structured, and tested at the method level. AI assists with implementation within that process.