Add existing to tracked

node_modules/@cesium/engine/Source/Scene/getMeshPrimitives.js

@@ -0,0 +1,72 @@
+import addAllToArray from "../Core/addAllToArray.js";
+import defined from "../Core/defined.js";
+import Frozen from "../Core/Frozen.js";
+import WebGLConstants from "../Core/WebGLConstants.js";
+
+/**
+ * Get an array of primitives for a given mesh. If the EXT_mesh_primitive_restart extension is present, use it to combine groups of primitives.
+ * If the extension is not present or its spec is violated, return the original mesh.primitives.
+ * @param {object} mesh A mesh from the glTF meshes array
+ * @returns {object[]} An array of mesh primitives
+ * @private
+ */
+function getMeshPrimitives(mesh) {
+  const meshExtensions = mesh.extensions ?? Frozen.EMPTY_OBJECT;
+  const primitiveRestartExtension = meshExtensions.EXT_mesh_primitive_restart;
+  const meshPrimitives = mesh.primitives;
+
+  if (!defined(primitiveRestartExtension)) {
+    return meshPrimitives;
+  }
+
+  // Note: per the spec, any violation of the extension's specification should cause us to fall back to mesh.primitives, if detecting the violation is feasible.
+
+  // Start with a copy of mesh.primitives. For each group, replace the first primitive in the group with a primitive representing the entire group,
+  // and set the rest of the primitives in the group to `undefined`.
+  // This allows us to identify which remaining primitives do not use primitive restart, and any errors involving a primitive appearing in more than one group.
+  const primitives = [];
+  addAllToArray(primitives, meshPrimitives);
+  for (const group of primitiveRestartExtension.primitiveGroups) {
+    // Spec: the group must not be empty and all indices must be valid array indices into mesh.primitives.
+    const firstPrimitiveIndex = group.primitives[0];
+    if (!defined(firstPrimitiveIndex) || !meshPrimitives[firstPrimitiveIndex]) {
+      return meshPrimitives;
+    }
+
+    const primitive = {
+      ...meshPrimitives[firstPrimitiveIndex],
+      indices: group.indices,
+    };
+
+    // Spec: primitive restart only supported for these topologies.
+    switch (primitive.mode) {
+      case WebGLConstants.TRIANGLE_FAN:
+      case WebGLConstants.TRIANGLE_STRIP:
+      case WebGLConstants.LINE_STRIP:
+      case WebGLConstants.LINE_LOOP:
+        break;
+      default:
+        return meshPrimitives;
+    }
+
+    for (const primitiveIndex of group.primitives) {
+      const thisPrimitive = primitives[primitiveIndex];
+
+      // Spec: all primitives must use indexed geometry and a given primitive may appear in at most one group.
+      // Spec: all primitives must have same topology.
+      if (
+        !defined(thisPrimitive?.indices) ||
+        thisPrimitive.mode !== primitive.mode
+      ) {
+        return meshPrimitives;
+      }
+
+      primitives[primitiveIndex] = undefined;
+    }
+
+    primitives[firstPrimitiveIndex] = primitive;
+  }
+
+  return primitives.filter(defined);
+}
+export default getMeshPrimitives;