Threejs Procedural Planets Agent Skill

Procedural Planets

Build a planet as a coupled field system evaluated on a unit direction. The same geological causes must drive geometry, color, roughness, normal, atmosphere handoff, and distance filtering.

Required build order

• Establish planet-space direction, radius, sea level, and world-unit scale.
• Build macro silhouette fields before any surface material.
• Add named geological structures: continents, basins, ridges, craters, lava fields, or ice.
• Derive slope, cavity, altitude, latitude, exposure, and shoreline fields.
• Classify broad biomes from those causes.
• Derive displacement, color, roughness, and normal from the shared field bundle.
• Filter bands by represented mesh scale and camera altitude.
• Couple the material to atmosphere and lighting using the same planet transform.

Read references/planet-field-and-atmosphere-systems.md for terrain, biome, gas-giant, material, altitude-LOD, and atmosphere-handoff mechanisms, including a known CPU/GPU field-parity failure mode.

Read the procedural planet surface implementation

and its shared terrain field

for undeformed sphere coordinates, shared CPU/GLSL terrain, coupled biome and

material causes, derivative bump, and altitude-filtered detail.

Non-negotiable constraints

• Domain-warp tangentially and renormalize; do not distort the sphere radially.
• Craters need floor, wall, rim, and optional ejecta—not dark circles.
• Continents and biomes must be region fields, not isolated threshold bubbles.
• Geometry displacement and shader normals must describe the same height function.
• Close detail may disappear with altitude; the macro silhouette may not.
• Expose individual field views and a displacement exaggeration mode.

Completion test

The body must remain intentional in:

• unlit silhouette;
• flat albedo with no atmosphere;
• grazing directional light;
• orbit view;
• close approach;
• biome-mask and normal-only views;
• at least three seeds without losing the chosen planetary identity.

Routing boundary

Use $threejs-procedural-fields for a reusable field bundle without a complete

body, and $threejs-atmosphere-aerial-perspective for scattering independent

of planet generation. This skill owns the coupled planetary surface.