Threejs Procedural Geometry Agent Skill

Procedural Geometry

Generate geometry from a semantic plan and an explicit coordinate frame. Triangle emission is the final compilation step, not the design model.

Build order

• Define dimensions and semantic segments.
• Generate a centerline, boundary, profile, or placement plan.
• Build the mechanism-appropriate local parameterization or branch orientation.
• Emit vertices with intentional seams and material ownership.
• Generate UVs from real distance.
• Validate winding, normals, tangents, bounds, and degenerates.
• Select merging, instancing, or LOD by update and material behavior.

Read references/profile-sweeps-and-mesh-writers.md

for the exact sculpted-frame profile, rail emission, tree rings, semantic mesh

writer, and their observed scaling limits.

Read the

sculpted gallery frame geometry

for the profile sweep, miter-like rail mapping, authored PBR surface

bundles, grazing spotlights, selective bloom ownership, and geometry

diagnostics.

Read

references/complete-submarine-assembly.md

for the exact dimensioned object contract, shared loft/sweep kernel, UV-owned

apertures, semantic subassemblies, generated fittings, and complete-model

diagnostics.

Read the

porcelain-and-brass submarine model

for a complete hard-surface assembly with a tilted-collar hull loft,

parallel-transport trim, furnished glass cabin, shrouded propeller, lens-section

fins, generated material inputs, and per-part triangle evidence.

Read

references/vehicle-loft-and-projector-contract.md

for parameter-curve section tracks, recess-opening sections, superellipse

volumes, spanwise airfoil lofts, warped outline plates, the two-plane paint

projector, load-deflected tyre carcasses, and their measured limits.

Read the

Formula One race car model

for one continuous nose-to-engine-cover loft driven by monotone parameter

tracks, a cockpit recess opened inside the section itself, superellipse sidepods

with a real inlet aperture, spanwise wing lofts, the livery projector, and a

contact-deflected tyre.

Read the

sport motorcycle model

for a slot-tagged mesh writer, revolve and upright-frame sweeps, offset panel

shells, spoked wheels with a rotor alpha mask, a hanging chain path, and a

volume-audited assembly.

Read the

procedural financial tower compiler

for semantic placement compilation and material-slot instancing at building

scale.

Failure conditions

• profile orientation flips along a curve;
• caps reuse side vertices and create averaged edge normals;
• UV scale changes with segment count;
• arbitrary vertex merging destroys hard edges or material boundaries;
• generated dimensions are hidden in magic multipliers;
• instancing is used despite per-instance topology differences;
• triangle count is the only reported complexity metric;
• apertures, frames, and glazing use unrelated coordinate systems;
• complete object parts are positioned by late visual nudges instead of a

shared dimension contract;

• a closed body ships inside-out because winding was never audited — check the

enclosed signed volume, since a wireframe pass cannot see it;

• a section track uses per-segment easing, so every knot has zero slope and the

lofted surface terraces under grazing light;

• a projected surface graphic is blended between planes without normalising the

weights, printing the same graphic twice on a 45-degree shoulder.

Routing boundary

This skill owns reusable mesh emission. Use

$threejs-procedural-materials when surface identity is primary,

$threejs-procedural-architecture for a building grammar, and

$threejs-procedural-vegetation for a growth hierarchy; those subject skills

may then apply these geometry mechanisms.