/threejs-water-optics

name: threejs-water-optics
description: Build production analytic and bounded water in Three.js. Use for photoreal shallow water with gravity-capillary FFT waves, dispersive caustics and diffraction glare, shared multi-wave displacement and normals, bounded RGBA heightfield pool simulation, local drops, object-driven ripples, differential-area caustics, ray-traced pool/water/sphere volume optics, derivative-filtered normal bands, analytic sky reflection, side-aware Fresnel, heuristic screen refraction, Beer-Lambert absorption, and crest foam.

Water Optics

Treat water as geometry motion, surface orientation, and a participating optical layer. A blue transparent material is not a water system.

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.

For large seas with spectral cascades, coastal breakers or camera-medium crossings, use `$threejs-spectral-ocean`. This skill also owns the air-side `photoreal-water` shallow-water compositor.

Analytic surface build order

1. Define wave bands and evaluate displacement. 2. Derive the normal analytically from the same waves. 3. Choose displaced geometry or explicitly normal-only water. 4. Establish scene-color ownership for heuristic refraction. 5. Declare whether absorption uses true depth or a fallback path-length estimate. 6. Blend analytic reflection/refraction through side-aware Fresnel. 7. Derive foam and glints from the shared wave response. 8. Filter unresolved normal bands from derivatives.

Read [references/water-surface-system.md](references/water-surface-system.md) for the authored displacement/normal contract, optical hierarchy, side-aware refraction, absorption fallback, and diagnostic channels.

Read the [interactive pool volume implementation](examples/interactive-pool-volume/water-volume-system.js) for bounded RGBA height/velocity/normal simulation, local drops, moving-sphere displacement suitable for draggable objects, differential-area caustics, and in-shader pool/water/sphere ray tracing against the pool bounds and sphere.

Read the [photoreal water implementation](examples/photoreal-water/photoreal-water.js) for gravity-capillary FFT waves, touch ripples, RGB caustics, refracted pebble-bed radiance and aperture diffraction glare. Read [references/photoreal-water.md](references/photoreal-water.md) for its pass, coordinate, filtering, integration and diagnostic contracts.

Failure conditions

• normal texture motion does not agree with displaced crests;
• heuristic refraction can sample foreground objects but the limitation is undisclosed;
• fallback path length is presented as reconstructed scene thickness;
• bounded pool caustics are a decorative projection detached from simulated

height normals;

• micro-waves alias into sparkling noise;
• foam is a scrolling texture unrelated to the shared crest metric;
• Fresnel is replaced by constant opacity;
• reflection, refraction, and transparency are all added without energy control.

Routing boundary

Use `$threejs-spectral-ocean` for large spectral cascades, Jacobian breaking, persistent ocean foam and camera-medium crossings. The `photoreal-water` example uses an FFT patch for shallow-water optics viewed from air; it does not implement underwater viewing. The analytic screen-refraction recipe also assumes an air-side camera above a bounded volume. Use `$threejs-precipitation-surfaces` for rain-driven puddle wetness, ripple masks, and weather-coupled splashes on ground surfaces. This skill owns authored analytic waves, bounded heightfield simulation, ray-traced pool-volume optics, and bounded-water optics.