threejs-parallax-occlusion-mapping

name	threejs-parallax-occlusion-mapping
description	Build silhouette-aware parallax occlusion mapping in Three.js WebGPU and TSL. Use for height-field ray marching, relief UVs, clipped flat or curved silhouettes, inflated shells, self-shadowing, relief-aware shadow depth, and height-derived normals.

Parallax Occlusion Mapping

Treat relief as a coupled intersection, coverage, normal, and shadow system. Do not stop at offsetting texture coordinates.

Build order

tangent frame and height convention
  -> view-ray march and hit refinement
  -> bounded or curved silhouette coverage
  -> shared marched sampling
  -> height-derived shading normal
  -> light-ray self-shadow march
  -> relief-aware cast/received shadow positions

Read references/silhouette-relief-contract.md for the intersection contract, flat and curved silhouette modes, shell inflation, shadow integration, quality controls, and diagnostics.

Read the silhouette relief implementation for the complete TSL march, binary hit refinement, gradient-safe sampling, coverage, horizon trimming, curved sag, and self-shadow function.

Read the complete bulkhead assembly and its packed procedural height maps for a wall, deck, relief columns, and overhead pipes using height-derived normals, inflated cylinder shells, alpha-to-coverage, shadow-mask carving, marched shadow depth, and received-shadow positions.

Required controls

• world or UV relief scale;
• minimum and maximum view-march layers;
• silhouette bounds and feathering;
• curved-surface curvature or curvature callback;
• horizon trimming and edge erosion;
• self-shadow steps, bias, and strength;
• geometry, carved, and full-relief shadow modes;
• height, coverage, marched UV, normal, and shadow diagnostics.

Failure conditions

• color, normal, and roughness rebuild separate view marches unintentionally;
• a curved host uses flat silhouette clipping at its geometric horizon;
• an inflated shell changes the relief floor instead of keeping it on the base surface;
• alpha-tested beauty coverage is assumed to carve shadow maps automatically;
• derivative sampling runs behind discard on drivers where it erodes coverage;
• grazing rays divide by an unbounded view-space Z component;
• relief self-shadowing darkens fill or emission indiscriminately.

Routing boundary

Use $threejs-procedural-materials when no ray-marched height intersection or silhouette ownership is required. Use $threejs-procedural-geometry when the silhouette must be actual mesh topology rather than a view-dependent relief.