Rhea

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Surface Voronoi

Scatter seeds across a surface, then give every point on that surface to whichever seed is nearest. The result is a cell partition — the structure of a dragonfly wing, a giraffe's coat, a soap foam, and a great deal of contemporary architecture.

Measured across the surface

“Nearest” is measured across the mesh, not through space. On a folded or branching form these are completely different: two points either side of a fold are close in straight-line distance and far apart along the surface.

A straight-line Voronoi on such a form produces cells that jump across gaps and wrap around edges in ways that make no physical sense. A geodesic one produces cells that behave the way cells in a real material behave, because a real material also has to get from one place to another by going along itself.

Seeding

Cells2 – 5000
Target number of cells. A target, not a guarantee — the spacing constraint can refuse to fit that many, in which case you get as many as would fit and the result line tells you how many.
Spacingfraction of mesh size
Minimum distance between seeds, as a fraction of the overall size. This is what makes the distribution Poisson-disk rather than uniform random, and it is why the cells come out evenly sized instead of clumped with gaps.
Seed
Makes the distribution reproducible. Change it for a different arrangement at the same density.
Density
An attribute or vertex group that biases where seeds land. Any field works: seed by curvature for small cells where the form bends, by occlusion for small cells in the recesses, by a reaction-diffusion pattern for cells that follow the branching.
Relax0 – 50 passes
Lloyd relaxation on the seeds themselves: each seed moves to the centre of its own cell, repeatedly. Three passes noticeably evens the sizes; ten gives a foam-like regularity. Set it to zero when you want the irregularity.

Random is not the same as even

Purely random seeds clump, leaving some cells tiny and others enormous. Poisson-disk sampling enforces a minimum separation, which is why natural cellular structures look even without looking like a grid. If your result has awkward tiny cells, raise the spacing before lowering the count.

Three outputs

Cell faces
One separated island of faces per cell. Each cell becomes its own piece of geometry, which is what you want for panelling, for per-cell materials, and for anything that will be fabricated as separate parts.
Cell borders
The boundaries between cells, swept into ribbons. This gives you the lattice — the dragonfly-wing look, and the input to a printed or milled cell structure.
Cell index
Writes the cell index per face as an attribute (default rhea_cell) and leaves the geometry alone. The most flexible output: your mesh is unchanged, and you have the partition available to drive anything else.

Border width matters more than it looks

A border of zero width is a plain edge. Edges carry no faces, so they cannot be rendered, shaded, or exported to anything that expects surfaces. If your border output appears in the viewport wireframe and nowhere else, that is why — give it a width.

Shaping the cells

Inset0 – 0.9
How far each cell shrinks toward its own centre. This is what opens gaps between cells and turns a partition into a pattern of separate plates. At high values the cells become small islands floating on the original surface.
Extrude±2
Displaces each cell along the surface normal. Combined with inset this gives you the stepped, scaled, plated look — cells lifted off the surface and separated from each other.
Extrude by field
Varies the extrusion per cell using the density attribute, so cells rise and fall across the form rather than all lifting equally. This is what makes a Voronoi result look grown rather than applied.
Border width
Half-width of the ribbon each border edge is swept into. Small values give a fine lattice; large ones give a heavy structural frame.

Combinations

  • Dragonfly wing. Cell borders, thin width, moderate cell count, three relax passes, on a flat or gently curved surface.
  • Cracked earth. Cell faces with a strong inset, no extrude, zero relax passes so the cells stay irregular.
  • Giraffe coat. Cell faces, small inset, no extrude, seeded evenly. Assign a material per cell index and you are done.
  • Bone foam. Cell borders on a closed form with a thickness field driving density, so the lattice densifies where the material is thin.
  • Two-scale structure. Run reaction-diffusion first, use it as the density attribute, and the cells crowd along the pattern branches while staying sparse between them.

Voronoi and Conway

A Conway ortho or chamfer result is an excellent surface to Voronoi, because the faces are even and the geodesic distances behave. Conversely, a Voronoi cell-face output run through Triangles to quads and then tessellated gives components sitting one per cell rather than one per original face.

Requirements and limits

  • The partition runs over the mesh's edge graph, so the mesh needs to be connected. Separate islands are partitioned independently, which is usually what you want but occasionally surprising.
  • Cell resolution is limited by mesh resolution. A hundred cells on a two-hundred-face mesh will produce ragged, blocky boundaries — the partition cannot be finer than the faces it is assigning. Subdivide first.
  • Very high cell counts on very dense meshes are the expensive case. Develop at a low count and raise it once the look is settled.