Initial commit

src/SplatGeometry.ts

@@ -0,0 +1,44 @@
+import * as THREE from "three";
+
+// SplatGeometry is an internal class used by ForgeRenderer to render a collection
+// of Gsplats in a single draw call by extending THREE.InstancedBufferGeometry.
+// Each Gsplat is drawn as two triangles, with the order of the Gsplats determined
+// by the instance attribute "ordering".
+
+export class SplatGeometry extends THREE.InstancedBufferGeometry {
+  ordering: Uint32Array;
+  attribute: THREE.InstancedBufferAttribute;
+
+  constructor(ordering: Uint32Array, activeSplats: number) {
+    super();
+
+    this.ordering = ordering;
+
+    this.setAttribute("position", new THREE.BufferAttribute(QUAD_VERTICES, 3));
+    this.setIndex(new THREE.BufferAttribute(QUAD_INDICES, 1));
+
+    // Hack to work around Three.js
+    // @ts-ignore
+    this._maxInstanceCount = ordering.length;
+    this.instanceCount = activeSplats;
+
+    this.attribute = new THREE.InstancedBufferAttribute(ordering, 1, false, 1);
+    this.attribute.setUsage(THREE.DynamicDrawUsage);
+    this.setAttribute("splatIndex", this.attribute);
+  }
+
+  update(ordering: Uint32Array, activeSplats: number) {
+    this.ordering = ordering;
+    this.attribute.array = ordering;
+    this.instanceCount = activeSplats;
+    this.attribute.addUpdateRange(0, activeSplats);
+    this.attribute.needsUpdate = true;
+  }
+}
+
+// Each instance draws to triangles covering a quad over coords (-1,-1,0)..(1,1,0)
+const QUAD_VERTICES = new Float32Array([
+  -1, -1, 0, 1, -1, 0, 1, 1, 0, -1, 1, 0,
+]);
+
+const QUAD_INDICES = new Uint16Array([0, 1, 2, 0, 2, 3]);