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Lighting & Shadows

PolyCSS shades each polygon with a Lambert model that matches three.js’s MeshLambertMaterial. A scene takes one directional light, one ambient light, and any number of point lights, set on <poly-scene> / PolyScene / createPolyScene(). Shading happens either once on the CPU (baked) or live in CSS calc() (dynamic) — see Lighting modes.

The light types are documented in the Core Types reference; this guide is the conceptual tour.

The light sources

Section titled “The light sources”

Directional light

Section titled “Directional light”

One infinitely-distant light with a single direction, color, and intensity — like the sun. Every surface gets color · intensity · max(0, n · L̂).

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Drag light ° / light ↑ to move the sun and watch the lit side — and the cast shadow on the ground — follow; intensity and ambient control brightness and fill.

import { createPolyScene, createPolyCamera } from "@layoutit/polycss";


const scene = createPolyScene(host, {
  camera: createPolyCamera({ rotX: 60, rotY: 30 }),
  directionalLight: { direction: [0.5, -0.6, 0.6], color: "#ffffff", intensity: 1 },
  ambientLight: { intensity: 0.3 },
});

Ambient light

Section titled “Ambient light”

A uniform fill with color and intensity (default 0.4) added to every surface regardless of orientation. Use it to lift shadowed faces out of pure black — exactly what a shadowed region fades toward.

Point lights

Section titled “Point lights”

Positional lights given as an array. Each has a world-space position, color, intensity, and optional castShadow. Point lights are direction-only — there is no distance falloff (they emulate three.js’s PointLight(distance: 0, decay: 0)); a surface is lit by color · intensity · max(0, n · L̂) where L̂ points from the surface to the light. Shading is flat per face — an accepted approximation of three.js’s per-fragment gradient, exact for small faces or distant lights.

Point lights are baked-mode only. Dynamic mode’s zero-JS light updates can’t express a per-face direction that varies with position, so dynamic scenes ignore pointLights entirely (shading and shadows). See Lighting modes.

const scene = createPolyScene(host, {
  camera: createPolyCamera({ rotX: 35, rotY: 20 }),
  // textureLighting defaults to "baked" — required for point lights.
  pointLights: [
    { position: [-4, 4, 5], color: "#ff7755", intensity: 1, castShadow: true },
    { position: [5, -3, 4], color: "#5599ff", intensity: 1, castShadow: true },
  ],
  ambientLight: { intensity: 0.3 },
});

Lighting modes

Section titled “Lighting modes”

textureLighting (scene-level, with a per-mesh override) chooses how the Lambert result is applied:

"baked" (default)"dynamic"
HowComputed once on the CPU, written into each leaf’s color / atlas pixelsResolved live in CSS calc() from scene-root variables + per-leaf normals
Point lights✅ Supported❌ Ignored (direction-only CSS can’t vary per position)
Moving the directional lightRe-bake needed for the lit surface (shadows update for free)Zero JS — just updates a CSS variable
Best forStatic scenes, point lights, exact colorLive / animated directional light, interactive light dragging

Rule of thumb: dynamic when the directional light moves every frame; baked when you want point lights or the lights are mostly static.

Cast shadows

Section titled “Cast shadows”

Shadows are CPU-projected SVG surfaces (not a render-strategy leaf). Mark casters with castShadow and receivers with receiveShadow:

scene.add(parsedFloor, { receiveShadow: true });
scene.add(parsedModel, { castShadow: true });
scene.setOptions({ shadow: { color: "#000000", opacity: 0.3, lift: 0.02 } });

What to expect:

  • Directional shadows work in both lighting modes and only appear for a directional light with intensity > 0 (intensity 0, or no directional light, casts nothing — matching three.js).
  • Point-light shadows are baked-mode only and radial (each vertex projects along its own ray from the light). Set castShadow: true on the point light and castShadow/receiveShadow on the meshes.
  • Colored multi-light shadows. Each light’s shadow is filled with the receiver lit by every other light, so a spot blocked from one colored light still shows the others’ color. Where two shadows overlap, the region composites to the both-blocked color (ambient only) — not a doubled-up black smear.
  • shadow.lift floats the shadow a hair above the receiver to avoid z-fighting; the default is fine, just don’t set it to exactly 0 on a coplanar floor.

Live & animated lights

Section titled “Live & animated lights”
  • Animating the directional light: use dynamic mode — moving the light is a single CSS-variable write per frame, no JS in the paint loop, and shadows re-project automatically.
  • Baked mode + a light change: cast shadows re-emit automatically (cheap SVG), but the baked lit surface stays frozen until you re-bake — call mesh.rebakeAtlas() (debounce it to the end of a drag; the atlas raster is the one costly step). The React/Vue components re-bake automatically on prop change, so this only applies to the imperative createPolyScene() API.
  • Animating point lights: baked-mode only, so re-bake per change (or per debounced step). For continuously moving lights, prefer a single directional light in dynamic mode.