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 stochastic seas driven by directional spectra and GPU FFTs, use $threejs-spectral-ocean instead.

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 for the authored displacement/normal contract, optical hierarchy, side-aware refraction, absorption fallback, and diagnostic channels.

Read the interactive pool volume implementation 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.

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 stochastic directional spectra, FFT cascades, Jacobian breaking, persistent ocean foam, and any interface the camera crosses — this skill's heuristic screen-refraction offset assumes a bounded volume seen from air, and an open interface needs that skill's forward projection instead. 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.