Support EXT_mesh_primitive_restart glTF extension

CHANGES.md

@@ -8,6 +8,10 @@
 
 - Removed the argument fallback in `ITwinData.*` functions. Please switch to the new options argument signature [#12778](https://github.com/CesiumGS/cesium/issues/12778)
 
+#### Additions :tada:
+
+- Added support for the [EXT_mesh_primitive_restart](https://github.com/KhronosGroup/glTF/pull/2478) glTF extension. [#12764](https://github.com/CesiumGS/cesium/issues/12764)
+
 ## 1.132 - 2025-08-01
 
 ### @cesium/engine

CONTRIBUTORS.md

@@ -101,6 +101,7 @@ See [CONTRIBUTING.md](CONTRIBUTING.md) for details on how to contribute to Cesiu
 - [Bentley Systems, Inc.](https://www.bentley.com)
   - [Paul Connelly](https://github.com/pmconne)
   - [Jason Crow](https://github.com/jason-crow)
+  - [Erin Ingram](https://github.com/eringram)
 - [Flightradar24 AB](https://www.flightradar24.com)
   - [Aleksei Kalmykov](https://github.com/kalmykov)
 - [BIT Systems](http://www.caci.com/bit-systems)

Specs/Data/Models/glTF-2.0/MeshPrimitiveRestart/glTF/MeshPrimitiveRestart.gltf

@@ -0,0 +1,315 @@
+{
+  "asset": {
+    "generator": "glTF-Transform v4.2.0",
+    "version": "2.0"
+  },
+  "accessors": [
+    {
+      "name": "Positions Accessor 0",
+      "type": "VEC3",
+      "componentType": 5126,
+      "count": 4,
+      "max": [
+        0.5,
+        0.5,
+        0
+      ],
+      "min": [
+        -0.5,
+        -0.5,
+        0
+      ],
+      "bufferView": 0,
+      "byteOffset": 0
+    },
+    {
+      "name": "Indices Accessor 0",
+      "type": "SCALAR",
+      "componentType": 5123,
+      "count": 3,
+      "bufferView": 1,
+      "byteOffset": 0
+    },
+    {
+      "name": "Indices Accessor 1",
+      "type": "SCALAR",
+      "componentType": 5123,
+      "count": 3,
+      "bufferView": 1,
+      "byteOffset": 8
+    },
+    {
+      "name": "Indices Accessor 2",
+      "type": "SCALAR",
+      "componentType": 5123,
+      "count": 3,
+      "bufferView": 1,
+      "byteOffset": 16
+    },
+    {
+      "name": "Indices Accessor 3",
+      "type": "SCALAR",
+      "componentType": 5123,
+      "count": 3,
+      "bufferView": 1,
+      "byteOffset": 24
+    },
+    {
+      "name": "Indices Accessor 4",
+      "type": "SCALAR",
+      "componentType": 5123,
+      "count": 2,
+      "bufferView": 1,
+      "byteOffset": 32
+    },
+    {
+      "name": "Indices Accessor 5",
+      "type": "SCALAR",
+      "componentType": 5123,
+      "count": 2,
+      "bufferView": 1,
+      "byteOffset": 36
+    },
+    {
+      "name": "Indices Accessor 6",
+      "type": "SCALAR",
+      "componentType": 5123,
+      "count": 2,
+      "bufferView": 1,
+      "byteOffset": 40
+    },
+    {
+      "name": "Indices Accessor 7",
+      "type": "SCALAR",
+      "componentType": 5123,
+      "count": 2,
+      "bufferView": 1,
+      "byteOffset": 44
+    },
+    {
+      "name": "All indices 0",
+      "type": "SCALAR",
+      "componentType": 5123,
+      "count": 7,
+      "bufferView": 2,
+      "byteOffset": 0
+    },
+    {
+      "name": "All indices 1",
+      "type": "SCALAR",
+      "componentType": 5123,
+      "count": 7,
+      "bufferView": 2,
+      "byteOffset": 16
+    },
+    {
+      "name": "All indices 2",
+      "type": "SCALAR",
+      "componentType": 5123,
+      "count": 5,
+      "bufferView": 2,
+      "byteOffset": 32
+    },
+    {
+      "name": "All indices 3",
+      "type": "SCALAR",
+      "componentType": 5123,
+      "count": 5,
+      "bufferView": 2,
+      "byteOffset": 44
+    },
+    {
+      "name": "Positions Accessor 1",
+      "type": "VEC3",
+      "componentType": 5126,
+      "count": 4,
+      "max": [
+        1.5,
+        1.5,
+        0
+      ],
+      "min": [
+        0.5,
+        0.5,
+        0
+      ],
+      "bufferView": 3,
+      "byteOffset": 0
+    }
+  ],
+  "bufferViews": [
+    {
+      "buffer": 0,
+      "byteOffset": 0,
+      "byteLength": 48,
+      "byteStride": 12,
+      "target": 34962
+    },
+    {
+      "buffer": 0,
+      "byteOffset": 48,
+      "byteLength": 48,
+      "target": 34963
+    },
+    {
+      "buffer": 0,
+      "byteOffset": 96,
+      "byteLength": 56
+    },
+    {
+      "buffer": 0,
+      "byteOffset": 152,
+      "byteLength": 48,
+      "byteStride": 12,
+      "target": 34962
+    }
+  ],
+  "buffers": [
+    {
+      "uri": "MeshPrimitiveRestart.bin",
+      "byteLength": 200
+    }
+  ],
+  "materials": [
+    {
+      "pbrMetallicRoughness": {
+        "baseColorFactor": [
+          0,
+          1,
+          0,
+          1
+        ]
+      }
+    },
+    {
+      "pbrMetallicRoughness": {
+        "baseColorFactor": [
+          0,
+          0,
+          1,
+          1
+        ]
+      }
+    }
+  ],
+  "meshes": [
+    {
+      "primitives": [
+        {
+          "attributes": {
+            "POSITION": 0
+          },
+          "mode": 5,
+          "material": 0,
+          "indices": 1
+        },
+        {
+          "attributes": {
+            "POSITION": 0
+          },
+          "mode": 5,
+          "material": 0,
+          "indices": 2
+        },
+        {
+          "attributes": {
+            "POSITION": 13
+          },
+          "mode": 6,
+          "material": 1,
+          "indices": 3
+        },
+        {
+          "attributes": {
+            "POSITION": 13
+          },
+          "mode": 6,
+          "material": 1,
+          "indices": 4
+        },
+        {
+          "attributes": {
+            "POSITION": 13
+          },
+          "mode": 3,
+          "material": 0,
+          "indices": 5
+        },
+        {
+          "attributes": {
+            "POSITION": 13
+          },
+          "mode": 3,
+          "material": 0,
+          "indices": 6
+        },
+        {
+          "attributes": {
+            "POSITION": 0
+          },
+          "mode": 2,
+          "material": 1,
+          "indices": 7
+        },
+        {
+          "attributes": {
+            "POSITION": 0
+          },
+          "mode": 2,
+          "material": 1,
+          "indices": 8
+        }
+      ],
+      "extensions": {
+        "EXT_mesh_primitive_restart": {
+          "primitiveGroups": [
+            {
+              "primitives": [
+                0,
+                1
+              ],
+              "indices": 9
+            },
+            {
+              "primitives": [
+                2,
+                3
+              ],
+              "indices": 10
+            },
+            {
+              "primitives": [
+                4,
+                5
+              ],
+              "indices": 11
+            },
+            {
+              "primitives": [
+                6,
+                7
+              ],
+              "indices": 12
+            }
+          ]
+        }
+      }
+    }
+  ],
+  "nodes": [
+    {
+      "mesh": 0
+    }
+  ],
+  "scenes": [
+    {
+      "nodes": [
+        0
+      ]
+    }
+  ],
+  "scene": 0,
+  "extensionsUsed": [
+    "EXT_mesh_primitive_restart"
+  ]
+}

packages/engine/Source/Scene/GltfLoader.js

@@ -33,6 +33,7 @@ import GltfGpmLoader from "./Model/Extensions/Gpm/GltfGpmLoader.js";
 import GltfMeshPrimitiveGpmLoader from "./Model/Extensions/Gpm/GltfMeshPrimitiveGpmLoader.js";
 import oneTimeWarning from "../Core/oneTimeWarning.js";
 import addAllToArray from "../Core/addAllToArray.js";
+import getMeshPrimitives from "./getMeshPrimitives.js";
 
 const {
   Attribute,
@@ -2432,7 +2433,7 @@ function loadNode(loader, gltfNode, frameState) {
   const meshId = gltfNode.mesh;
   if (defined(meshId)) {
     const mesh = loader.gltfJson.meshes[meshId];
-    const primitives = mesh.primitives;
+    const primitives = getMeshPrimitives(mesh);
     for (let i = 0; i < primitives.length; ++i) {
       node.primitives.push(
         loadPrimitive(

packages/engine/Source/Scene/Model/Model.js

@@ -72,6 +72,9 @@ import ModelImagery from "./ModelImagery.js";
  *  {@link https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Vendor/EXT_mesh_gpu_instancing|EXT_mesh_gpu_instancing}
  *  </li>
  *  <li>
+ *  {@link https://github.com/KhronosGroup/glTF/pull/2514|EXT_mesh_primitive_restart}
+ *  </li>
+ *  <li>
  *  {@link https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Vendor/EXT_meshopt_compression|EXT_meshopt_compression}
  *  </li>
  *  <li>