feat: 3 scene rendering setup

apps/viewer/src/viewerUniverseLayer.ts

@@ -0,0 +1,25 @@
+import * as THREE from "three";
+
+/**
+ * Universe rendering layer — always the first layer rendered.
+ * Contains the infinite backdrop: backdrop stars and nebula clouds.
+ * Has no dedicated camera; rendered with whichever camera is active for the current POV
+ * so the backdrop always aligns with the foreground view.
+ */
+export class UniverseLayer {
+  readonly scene = new THREE.Scene();
+
+  /** Backdrop stars and nebula clouds. Follows the active camera to act as a skybox. */
+  readonly ambienceGroup = new THREE.Group();
+
+  constructor() {
+    this.scene.background = new THREE.Color(0x040912);
+    this.scene.add(this.ambienceGroup);
+  }
+
+  updateAmbience(activeCamera: THREE.Camera, delta: number) {
+    this.ambienceGroup.position.copy(activeCamera.position);
+    this.ambienceGroup.rotation.y += delta * 0.005;
+    this.ambienceGroup.rotation.x = Math.sin(performance.now() * 0.00003) * 0.015;
+  }
+}