Merge pull request #12706 from CesiumGS/gsplat-modelmatrix-update

Update with modelMatrix and correctly handle rotation

Author: jjspace

CHANGES.md

@@ -9,6 +9,8 @@
 - Updates use of deprecated options on createImageBitmap. [#12664](https://github.com/CesiumGS/cesium/pull/12664)
 - Fixed raymarching step size for cylindrical voxels. [#12681](https://github.com/CesiumGS/cesium/pull/12681)
 
+- Fixes handling of tileset modelMatrix changes for translations and rotations in GaussianSplatPrimitive. [#12706](https://github.com/CesiumGS/cesium/pull/12706)
+
 #### Additions :tada:
 
 - Added `HeightReference` to `Cesium3DTileset.ConstructorOptions` to allow clamping point features in 3D Tile vector data to terrain or 3D Tiles [#11710](https://github.com/CesiumGS/cesium/pull/11710)

packages/engine/Source/Scene/GaussianSplat3DTileContent.js

@@ -5,6 +5,8 @@ import RuntimeError from "../Core/RuntimeError.js";
 import Axis from "./Axis.js";
 import GaussianSplatPrimitive from "./GaussianSplatPrimitive.js";
 import destroyObject from "../Core/destroyObject.js";
+import ModelUtility from "./Model/ModelUtility.js";
+import VertexAttributeSemantic from "./VertexAttributeSemantic.js";
 
 /**
  * Represents the contents of a glTF or glb using the {@link https://github.com/CesiumGS/glTF/tree/draft-spz-splat-compression/extensions/2.0/Khronos/KHR_spz_gaussian_splats_compression|KHR_spz_gaussian_splats_compression} extension.
@@ -28,6 +30,17 @@ 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.
+   * @type {undefined|Float32Array}
+   * @private
+   */
+  this._originalPositions = undefined;
+  this._originalRotations = undefined;
+  this._originalScales = undefined;
+
   /**
    * glTF primitive data that contains the Gaussian splat data needed for rendering.
    * @type {undefined|Primitive}
@@ -350,19 +363,15 @@ GaussianSplat3DTileContent.fromGltf = async function (
 
 /**
  * Updates the content of the tile and prepares it for rendering.
- * @param {Cesium3DTileset}
+ * @param {Cesium3DTileset}Data attribution
  * @param {FrameState} frameState - The current frame state.
  * @private
  */
 GaussianSplat3DTileContent.prototype.update = function (primitive, frameState) {
   const loader = this._loader;
 
   if (this._ready) {
-    if (
-      !this._transformed &&
-      this._tile !== primitive.root &&
-      primitive.root.content.ready
-    ) {
+    if (!this._transformed && primitive.root.content.ready) {
       GaussianSplatPrimitive.transformTile(this._tile);
       this._transformed = true;
     }
@@ -382,6 +391,27 @@ GaussianSplat3DTileContent.prototype.update = function (primitive, frameState) {
     this.worldTransform = loader.components.scene.nodes[0].matrix;
     this._ready = true;
 
+    this._originalPositions = new Float32Array(
+      ModelUtility.getAttributeBySemantic(
+        this.splatPrimitive,
+        VertexAttributeSemantic.POSITION,
+      ).typedArray,
+    );
+
+    this._originalRotations = new Float32Array(
+      ModelUtility.getAttributeBySemantic(
+        this.splatPrimitive,
+        VertexAttributeSemantic.ROTATION,
+      ).typedArray,
+    );
+
+    this._originalScales = new Float32Array(
+      ModelUtility.getAttributeBySemantic(
+        this.splatPrimitive,
+        VertexAttributeSemantic.SCALE,
+      ).typedArray,
+    );
+
     return;
   }
 

packages/engine/Source/Scene/GaussianSplatPrimitive.js

@@ -29,7 +29,6 @@ import AttributeType from "./AttributeType.js";
 import ModelComponents from "./ModelComponents.js";
 import Axis from "./Axis.js";
 import Cartesian3 from "../Core/Cartesian3.js";
-import Transforms from "../Core/Transforms.js";
 import Quaternion from "../Core/Quaternion.js";
 import SplitDirection from "./SplitDirection.js";
 import destroyObject from "../Core/destroyObject.js";
@@ -438,27 +437,31 @@ GaussianSplatPrimitive.transformTile = function (tile) {
     computedModelMatrix,
   );
 
-  const center = tile.tileset.boundingSphere.center;
-  const toGlobal = Transforms.eastNorthUpToFixedFrame(center);
-  const toLocal = Matrix4.inverse(toGlobal, scratchMatrix4B);
-
+  const toGlobal = Matrix4.multiply(
+    tile.tileset.modelMatrix,
+    Matrix4.fromArray(tile.tileset.root.transform),
+    scratchMatrix4B,
+  );
+  const toLocal = Matrix4.inverse(toGlobal, scratchMatrix4C);
   const transform = Matrix4.multiplyTransformation(
     toLocal,
     computedModelMatrix,
     scratchMatrix4A,
   );
-
-  const positions = ModelUtility.getAttributeBySemantic(
+  const positions = tile.content._originalPositions;
+  const rotations = tile.content._originalRotations;
+  const scales = tile.content._originalScales;
+  const attributePositions = ModelUtility.getAttributeBySemantic(
     splatPrimitive,
     VertexAttributeSemantic.POSITION,
   ).typedArray;
 
-  const rotations = ModelUtility.getAttributeBySemantic(
+  const attributeRotations = ModelUtility.getAttributeBySemantic(
     splatPrimitive,
     VertexAttributeSemantic.ROTATION,
   ).typedArray;
 
-  const scales = ModelUtility.getAttributeBySemantic(
+  const attributeScales = ModelUtility.getAttributeBySemantic(
     splatPrimitive,
     VertexAttributeSemantic.SCALE,
   ).typedArray;
@@ -493,18 +496,18 @@ GaussianSplatPrimitive.transformTile = function (tile) {
     Matrix4.getRotation(scratchMatrix4C, rotation);
     Matrix4.getScale(scratchMatrix4C, scale);
 
-    positions[i * 3] = position.x;
-    positions[i * 3 + 1] = position.y;
-    positions[i * 3 + 2] = position.z;
+    attributePositions[i * 3] = position.x;
+    attributePositions[i * 3 + 1] = position.y;
+    attributePositions[i * 3 + 2] = position.z;
 
-    rotations[i * 4] = rotation.x;
-    rotations[i * 4 + 1] = rotation.y;
-    rotations[i * 4 + 2] = rotation.z;
-    rotations[i * 4 + 3] = rotation.w;
+    attributeRotations[i * 4] = rotation.x;
+    attributeRotations[i * 4 + 1] = rotation.y;
+    attributeRotations[i * 4 + 2] = rotation.z;
+    attributeRotations[i * 4 + 3] = rotation.w;
 
-    scales[i * 3] = scale.x;
-    scales[i * 3 + 1] = scale.y;
-    scales[i * 3 + 2] = scale.z;
+    attributeScales[i * 3] = scale.x;
+    attributeScales[i * 3 + 1] = scale.y;
+    attributeScales[i * 3 + 2] = scale.z;
   }
 };
 
@@ -706,8 +709,11 @@ GaussianSplatPrimitive.buildGSplatDrawCommand = function (
 
   primitive._vertexArrayLen = primitive._indexes.length;
 
-  const center = tileset.boundingSphere.center;
-  const modelMatrix = Transforms.eastNorthUpToFixedFrame(center);
+  const modelMatrix = Matrix4.multiply(
+    tileset.modelMatrix,
+    Matrix4.fromArray(tileset.root.transform),
+    scratchMatrix4B,
+  );
 
   const command = new DrawCommand({
     boundingVolume: tileset.boundingSphere,
@@ -751,6 +757,11 @@ GaussianSplatPrimitive.prototype.update = function (frameState) {
     frameState.commandList.push(this._drawCommand);
   }
 
+  if (tileset._modelMatrixChanged) {
+    this._dirty = true;
+    return;
+  }
+
   if (frameState.passes.pick === true) {
     return;
   }