GaussianSplatPrimitive Multiple Instances Fix

CHANGES.md

@@ -12,7 +12,8 @@
 #### Fixes :wrench:
 
 - Removes the minimum tile threshold of four for WMTS. [#4372](https://github.com/CesiumGS/cesium/issues/4372)
-- Fixed a crash that could happen when loading PNTS (point cloud) data that contained a batch table without a binary part [#11166](https://github.com/CesiumGS/cesium/issues/11166)
+- Fixes issue where multiple instances of a Gaussian splat tileset would transform tile positions incorrectly and render out of position. [12795](https://github.com/CesiumGS/cesium/issues/12795)
+- Fixed a crash that could happen when loading PNTS (point cloud) data that contained a batch table without a binary part. [#11166](https://github.com/CesiumGS/cesium/issues/11166)
 
 #### Additions :tada:
 

packages/engine/Source/Scene/GaussianSplat3DTileContent.js

@@ -32,15 +32,14 @@ function GaussianSplat3DTileContent(loader, tileset, tile, resource) {
   }
 
   /**
-   * Original position, scale and rotation values for splats. Used to maintain
-   * consistency when multiple transforms may occur. Downstream consumers otherwise may not know
-   * the underlying data was modified.
+   * Local copies of attribute buffers with transformed values. Originals are kept in the gltf loader.
+   * These are the buffers that are used for rendering.
    * @type {undefined|Float32Array}
    * @private
    */
-  this._originalPositions = undefined;
-  this._originalRotations = undefined;
-  this._originalScales = undefined;
+  this._positions = undefined;
+  this._rotations = undefined;
+  this._scales = undefined;
 
   /**
    * glTF primitive data that contains the Gaussian splat data needed for rendering.
@@ -347,6 +346,24 @@ Object.defineProperties(GaussianSplat3DTileContent.prototype, {
       this._group = value;
     },
   },
+
+  positions: {
+    get: function () {
+      return this._positions;
+    },
+  },
+
+  rotations: {
+    get: function () {
+      return this._rotations;
+    },
+  },
+
+  scales: {
+    get: function () {
+      return this._scales;
+    },
+  },
 });
 
 /**
@@ -429,21 +446,21 @@ GaussianSplat3DTileContent.prototype.update = function (primitive, frameState) {
     this.worldTransform = loader.components.scene.nodes[0].matrix;
     this._ready = true;
 
-    this._originalPositions = new Float32Array(
+    this._positions = new Float32Array(
       ModelUtility.getAttributeBySemantic(
         this.splatPrimitive,
         VertexAttributeSemantic.POSITION,
       ).typedArray,
     );
 
-    this._originalRotations = new Float32Array(
+    this._rotations = new Float32Array(
       ModelUtility.getAttributeBySemantic(
         this.splatPrimitive,
         VertexAttributeSemantic.ROTATION,
       ).typedArray,
     );
 
-    this._originalScales = new Float32Array(
+    this._scales = new Float32Array(
       ModelUtility.getAttributeBySemantic(
         this.splatPrimitive,
         VertexAttributeSemantic.SCALE,

packages/engine/Source/Scene/GaussianSplatPrimitive.js

@@ -421,9 +421,9 @@ GaussianSplatPrimitive.transformTile = function (tile) {
     computedModelMatrix,
     scratchMatrix4A,
   );
-  const positions = tile.content._originalPositions;
-  const rotations = tile.content._originalRotations;
-  const scales = tile.content._originalScales;
+  const positions = tile.content.positions;
+  const rotations = tile.content.rotations;
+  const scales = tile.content.scales;
   const attributePositions = ModelUtility.getAttributeBySemantic(
     splatPrimitive,
     VertexAttributeSemantic.POSITION,
@@ -442,19 +442,19 @@ GaussianSplatPrimitive.transformTile = function (tile) {
   const position = new Cartesian3();
   const rotation = new Quaternion();
   const scale = new Cartesian3();
-  for (let i = 0; i < positions.length / 3; ++i) {
-    position.x = positions[i * 3];
-    position.y = positions[i * 3 + 1];
-    position.z = positions[i * 3 + 2];
+  for (let i = 0; i < attributePositions.length / 3; ++i) {
+    position.x = attributePositions[i * 3];
+    position.y = attributePositions[i * 3 + 1];
+    position.z = attributePositions[i * 3 + 2];
 
-    rotation.x = rotations[i * 4];
-    rotation.y = rotations[i * 4 + 1];
-    rotation.z = rotations[i * 4 + 2];
-    rotation.w = rotations[i * 4 + 3];
+    rotation.x = attributeRotations[i * 4];
+    rotation.y = attributeRotations[i * 4 + 1];
+    rotation.z = attributeRotations[i * 4 + 2];
+    rotation.w = attributeRotations[i * 4 + 3];
 
-    scale.x = scales[i * 3];
-    scale.y = scales[i * 3 + 1];
-    scale.z = scales[i * 3 + 2];
+    scale.x = attributeScales[i * 3];
+    scale.y = attributeScales[i * 3 + 1];
+    scale.z = attributeScales[i * 3 + 2];
 
     Matrix4.fromTranslationQuaternionRotationScale(
       position,
@@ -469,18 +469,18 @@ GaussianSplatPrimitive.transformTile = function (tile) {
     Matrix4.getRotation(scratchMatrix4C, rotation);
     Matrix4.getScale(scratchMatrix4C, scale);
 
-    attributePositions[i * 3] = position.x;
-    attributePositions[i * 3 + 1] = position.y;
-    attributePositions[i * 3 + 2] = position.z;
+    positions[i * 3] = position.x;
+    positions[i * 3 + 1] = position.y;
+    positions[i * 3 + 2] = position.z;
 
-    attributeRotations[i * 4] = rotation.x;
-    attributeRotations[i * 4 + 1] = rotation.y;
-    attributeRotations[i * 4 + 2] = rotation.z;
-    attributeRotations[i * 4 + 3] = rotation.w;
+    rotations[i * 4] = rotation.x;
+    rotations[i * 4 + 1] = rotation.y;
+    rotations[i * 4 + 2] = rotation.z;
+    rotations[i * 4 + 3] = rotation.w;
 
-    attributeScales[i * 3] = scale.x;
-    attributeScales[i * 3 + 1] = scale.y;
-    attributeScales[i * 3 + 2] = scale.z;
+    scales[i * 3] = scale.x;
+    scales[i * 3 + 1] = scale.y;
+    scales[i * 3 + 2] = scale.z;
   }
 };
 
@@ -767,57 +767,54 @@ GaussianSplatPrimitive.prototype.update = function (frameState) {
       const aggregateAttributeValues = (
         componentDatatype,
         getAttributeCallback,
+        numberOfComponents,
       ) => {
         let aggregate;
         let offset = 0;
         for (const tile of tiles) {
-          const primitive = tile.content.splatPrimitive;
-          const attribute = getAttributeCallback(primitive);
+          const content = tile.content;
+          const attribute = getAttributeCallback(content);
+          const componentsPerAttribute = defined(numberOfComponents)
+            ? numberOfComponents
+            : AttributeType.getNumberOfComponents(attribute.type);
+          const buffer = defined(attribute.typedArray)
+            ? attribute.typedArray
+            : attribute;
           if (!defined(aggregate)) {
             aggregate = ComponentDatatype.createTypedArray(
               componentDatatype,
-              totalElements *
-                AttributeType.getNumberOfComponents(attribute.type),
+              totalElements * componentsPerAttribute,
             );
           }
-          aggregate.set(attribute.typedArray, offset);
-          offset += attribute.typedArray.length;
+          aggregate.set(buffer, offset);
+          offset += buffer.length;
         }
         return aggregate;
       };
 
       this._positions = aggregateAttributeValues(
         ComponentDatatype.FLOAT,
-        (splatPrimitive) =>
-          ModelUtility.getAttributeBySemantic(
-            splatPrimitive,
-            VertexAttributeSemantic.POSITION,
-          ),
+        (content) => content.positions,
+        3,
       );
 
       this._scales = aggregateAttributeValues(
         ComponentDatatype.FLOAT,
-        (splatPrimitive) =>
-          ModelUtility.getAttributeBySemantic(
-            splatPrimitive,
-            VertexAttributeSemantic.SCALE,
-          ),
+        (content) => content.scales,
+        3,
       );
 
       this._rotations = aggregateAttributeValues(
         ComponentDatatype.FLOAT,
-        (splatPrimitive) =>
-          ModelUtility.getAttributeBySemantic(
-            splatPrimitive,
-            VertexAttributeSemantic.ROTATION,
-          ),
+        (content) => content.rotations,
+        4,
       );
 
       this._colors = aggregateAttributeValues(
         ComponentDatatype.UNSIGNED_BYTE,
-        (splatPrimitive) =>
+        (content) =>
           ModelUtility.getAttributeBySemantic(
-            splatPrimitive,
+            content.splatPrimitive,
             VertexAttributeSemantic.COLOR,
           ),
       );