/threejs-shadow-systems

name: threejs-shadow-systems
description: Implement stable, scalable directional-shadow systems for Three.js. Use for large procedural worlds, city scenes, terrain, moving cameras, WebGPU/TSL shadow nodes, cascades, cached clipmaps, texel stabilization, update budgets, and targeted invalidation.

Shadow Systems

Use a single shadow map only when its receiver region is genuinely bounded. For large moving views, make shadow coverage an explicit spatial hierarchy.

Cached clipmap workflow

1. Define concentric light-space square levels. 2. Snap each level center to its own texel grid. 3. Cross-fade adjacent levels in shader space. 4. Refresh near levels continuously. 5. Cache coarse levels and update them under a frame budget. 6. Invalidate intersecting levels when important casters or streamed terrain change. 7. Scale normal bias by world-space texel width.

Read [references/cached-clipmap-shadows.md](references/cached-clipmap-shadows.md) before implementing a large-world directional light.

Read the [cached shadow clipmaps](../threejs-procedural-architecture/examples/procedural-financial-tower/shadow-clipmaps.js) for three light-space square levels, per-level texel snapping, containment cross-fades, cached coarse updates, scaled bias, and unshadowed outside weight.

Failure conditions

• projection centers move by fractions of a texel;
• shader containment does not match the map's committed center;
• all cascades refresh every frame without evidence;
• coarse levels freeze moving casters indefinitely;
• depth texture samples occur in divergent fragment control flow;
• the same normal bias is used across radically different texel sizes;
• level boundaries become visible under camera motion.

Routing boundary

Use this skill for light-space directional shadow maps. Use `$threejs-screen-space-ambient-occlusion` for view-dependent ambient visibility; AO is not a replacement for cast shadows.