First commit

app/three/utils/build-default-lights.ts

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+import { AmbientLight, DirectionalLight, Scene } from "three";
+
+const DEG2RAD = Math.PI / 180;
+export function buildDefaultLights(scene: Scene) {
+  // ambient light
+  scene.add(new AmbientLight(0x999999));
+
+  // directional lights
+  const opt = {
+    azimuth: 220,
+    altitude: 45,
+  };
+
+  const lambda = (90 - opt.azimuth) * DEG2RAD;
+  const phi = opt.altitude * DEG2RAD;
+
+  const x = Math.cos(phi) * Math.cos(lambda);
+  const y = Math.cos(phi) * Math.sin(lambda);
+  const z = Math.sin(phi);
+
+  const light1 = new DirectionalLight(0xffffff, 0.5);
+  light1.position.set(x, y, z);
+  scene.add(light1);
+
+  // thin light from the opposite direction
+  const light2 = new DirectionalLight(0xffffff, 0.1);
+  light2.position.set(-x, -y, -z);
+  scene.add(light2);
+}