# Threejs Parallax Occlusion Mapping

> 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.

- Skill: `gabrielmoreira/threejs-parallax-occlusion-mapping` (Agent Skill, multi-file: 6 files)
- Install (CLI): `npx skillmds@latest add gabrielmoreira/threejs-parallax-occlusion-mapping`
- Raw SKILL.md: https://api.skillmd.com/api/skills/gabrielmoreira/threejs-parallax-occlusion-mapping/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: gabrielmoreira (https://skillmd.com/u/gabrielmoreira)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/gabrielmoreira/threejs-parallax-occlusion-mapping

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# Parallax Occlusion Mapping

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

This skill contains exemplary examples and assets beyond descriptive guidance,
they're worth studying, referencing, or even copying. Use them sufficiently
when relevant and do NOT blindly skip them.

## Build order

```text
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](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](examples/silhouette-relief/ParallaxOcclusion.js)
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](examples/silhouette-relief/silhouette-relief-system.js)
and its [packed procedural height maps](examples/silhouette-relief/bulkhead-height-maps.js)
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.