GeoNodus — procedural geometry engine

What GeoNodus is

A shared library that brings procedural, Houdini-style modeling to your own applications and games. It doesn't need Houdini, a license server or a network connection. Everything is computed on the device.

API that mirrors HAPI

The gn* functions and GN_* types follow Houdini Engine one to one: sessions, node IDs, string handles, flat parameter arrays, Compose*/GetComposed*, parts, attributes and groups. Code written against HAPI ports with little more than a rename.

Run-time parametric modeling

You can build complex scenes out of networks with hundreds of nodes. Any parameter can change while the app is running. Dirty propagation re-cooks only the affected nodes, on a separate cook thread, so the UI never blocks.

Dynamic, animated scenes

Parameters accept expressions with time variables ($T, $F) and ch() references between nodes. Renaming a node or a parameter keeps every reference intact. Spare parameters and sub-networks are supported, and a whole graph can be saved to JSON and loaded back.

Houdini Engine (HAPI)C

HAPI_CreateNode(&session, geo, "box", "box1", false, &box);
HAPI_SetParmFloatValues(&session, box, &size, idx, 3);
HAPI_CookNode(&session, box, nullptr);
HAPI_GetPartInfo(&session, box, 0, &part);

GeoNodusC

gnCreateNode(session, geo, "box", "box1", false, &box);
gnSetParmFloatValues(session, box, &size, idx, 3);
gnCookNode(session, box, nullptr);
gnGetPartInfo(session, box, 0, &part);

What already works

Screenshots from the GeoNodus desktop client, a Qt test application built on top of the library. Each screenshot shows the 3D viewport, the node network, the parameter panel and the geometry spreadsheet. The operators reproduce Houdini's behavior and are verified against reference results exported from Houdini. Click a screenshot to open it at full size.

Screenshot	Implemented functionality
	01 · OBJECTS & PRIMITIVES Scene objects and generators An object-level scene (`/obj`) with several geometry objects, each holding its own SOP network. Generators: Box, Sphere (polygon mesh and icosahedral polygon), Torus, Grid, Circle, and NURBS / Bezier curves. The full object Transform tab: transform and rotation order, pivot, uniform scale, pre-transform, Keep Position When Parenting, Child Compensation. Object parenting and world transforms; the viewport shows points and curve hulls. boxspheretoruscirclenull
	02 · ATTRIBUTES Attribute Create & Attribute Randomize Each point of a sphere gets a random color (`Cd`). The spreadsheet below the viewport reads positions and colors straight from the library. Point, vertex, primitive and detail attributes: int, float and string, with sizes 1–4 and type info. Paged, copy-on-write attribute storage shared between nodes; operations are limited to group members. A HAPI-style attribute API: `gnGetAttributeInfo`, `gnGetAttributeFloatData`, … attribcreateattribrandomize
	03 · GROUPS Group Range & Group Create Every second primitive of a box goes into group `gr` (Select 1 of 2); random colors are then applied to the group alone. Ranges: start/end, relative, equal partitions, inversion, select N of M with offset. Per-connected-piece ranges, collision groups and merge methods. Group Create can filter by bounding region, normal, edge angle/length and random chance; point, primitive and edge groups are supported. grouprangegroupcreate
	04 · CUTTING Clip with capping A torus is cut by a plane and the openings are filled with caps. Only the caps (group `filled`) are recolored. Keep above, below or both sides; set origin, direction, distance and snap tolerance. Attributes are interpolated onto the new points; caps with holes are bridged the same way as in Houdini. The Normal SOP recomputes point, vertex, primitive or detail normals with a cusp angle. clipnormal
	05 · DISTRIBUTION Scatter Thousands of points are spread evenly over a sphere's surface, and each one inherits the color of the surface beneath it. Sets a total count, a density, or a density attribute; also scatters per primitive or in texture space. Relax iterations push points apart for an even, blue-noise-like layout, using a parallel BVH. Transfers attributes and groups from the source surface; writes `sourceprim` and `sourceprimuv`. scatter
	06 · INSTANCING Copy to Points A torus is copied onto points scattered over a grid. Every copy picks up the random color of its target point, giving thousands of objects that update interactively. Orients and scales copies by `N`, `up`, `orient`, `pscale`, `scale`, `trans` and `transform`. Can copy, multiply, add or subtract attributes from the target, and copies target groups. Copy and Transform makes N copies with incremental transforms. copytopointscopyxformgrid
$Torus deformed by fractal noise$	07 · NOISE Mountain Fractal noise pushes a torus's points along their normals and turns it into an organic shape. A Unified Noise implementation: Perlin, Simplex, Worley, Alligator, Flow, Sparse and Sinusoid bases. Fractals: Standard (fBm), Terrain and Hybrid Terrain, with octaves, lacunarity and roughness. Fold, Complement, Gain/Bias, clipping, Lattice and Gradient Warp; time-dependent noise for animation. mountain
	08 · DEFORMATION Bend A bend deformer applied to a torus inside a capture region, with random per-primitive colors. Bend by angle or goal direction, plus Twist, Length Scale (with Preserve Volume), Taper and Squish, and a profile ramp. Capture origin, direction, length and up vector; limit the deformation or deform in both directions. Vectors, normals and quaternions are transformed through the deformation Jacobian. bendxform
	09 · MODELING PolyExtrude The faces in group `gr` from the previous step are extruded with an inset, turning the flat stripes into raised ribs. Extrudes individual elements or connected components; settings include distance, inset, twist, divisions and thickness/twist ramps. Can extrude along a curve from the second input; also extrudes open curves into ribbons. Front, back and side output groups; unwrapped UVs for the sides; vertex normals. polyextrude
	10 · MODELING PolyBevel Every edge of a box is rounded with a 12-division fillet. Corner patches are generated and normals are recomputed afterwards. Bevels edges and points; fillet shapes are Round, Chamfer, Crease, Solid and None. Profiles come from a ramp or a curve; sampling can be uniform, adaptive or by control points. Collision detection, sliding on ring edges and stop-loop limits. polybevelnormal
	11 · BOOLEANS Boolean Boolean operations on polygon meshes, with attributes transferred to the result. Union, Intersect, Subtract (A − B, B − A or both) and Shatter into pieces of A, B or both. Point, vertex, primitive and detail attributes and groups are carried over from both inputs, and values are interpolated at the new points along the seam. boolean
	12 · UV UV Texture A torus, a sphere and a box each get texture coordinates from their own UV Texture node and are combined into one geometry with Merge. The test texture shows how the UVs are laid out. Projections: Orthographic, Polar, Cylindrical, Face, Rows & Columns and Modify Source; Uniform, Average and Arc Length spacing for curves. UVs are stored on points or vertices (or chosen automatically), with scale, offset, rotation and Fix Boundary Seams. Merge combines up to 10 inputs and unites their attributes, types and groups the way Houdini does. texturemergetorusspherebox
	13 · ANIMATION Channels and expressions An animated castle scene with about 130 nodes. Its timing, tower count, wall radius and wind are read from the channels of the null object `ctrl`; the parameters highlighted in green there are driven by expressions. Any parameter component can hold an expression with time variables (`$T`, `$F`, `$FPS`, …) and math functions. `ch()` references read other parameters by absolute or relative path, and the paths are updated when a node is renamed. Changing the time recooks only the nodes that depend on it; object transforms and parenting work as in Houdini. nullgeoch()$T