First draft for merging structural metadata

src/gltf-extensions/gltfExtensions/EXTStructuralMetadata.ts

@@ -995,7 +995,7 @@ export class EXTStructuralMetadata extends Extension {
       structuralMetadataDef.schema = schemaDef;
     }
     const schemaUri = structuralMetadata.getSchemaUri();
-    if (schemaUri !== undefined) {
+    if (schemaUri !== null) {
       structuralMetadataDef.schemaUri = schemaUri;
     }
 

src/gltf-extensions/gltfExtensions/StructuralMetadata.ts

@@ -25,7 +25,7 @@ const NAME = "EXT_structural_metadata";
 
 interface IStructuralMetadata extends IProperty {
   schema: Schema;
-  schemaUri: string;
+  schemaUri: string | null;
   propertyTables: PropertyTable[];
   propertyTextures: PropertyTexture[];
   propertyAttributes: PropertyAttribute[];
@@ -179,6 +179,8 @@ export class StructuralMetadata extends ExtensionProperty<IStructuralMetadata> {
 
   protected override getDefaults() {
     return Object.assign(super.getDefaults(), {
+      schema: null,
+      schemaUri: null,
       propertyTables: [],
       propertyTextures: [],
       propertyAttributes: [],
@@ -192,11 +194,11 @@ export class StructuralMetadata extends ExtensionProperty<IStructuralMetadata> {
     return this.setRef("schema", schema);
   }
 
-  getSchemaUri(): string {
+  getSchemaUri(): string | null {
     return this.get("schemaUri");
   }
-  setSchemaUri(name: string) {
-    return this.set("schemaUri", name);
+  setSchemaUri(schemaUri: string | null) {
+    return this.set("schemaUri", schemaUri);
   }
 
   listPropertyTables(): PropertyTable[] {

src/tools/gltfExtensionsUtils/StructuralMetadataMergeUtilities.ts

@@ -0,0 +1,108 @@
+// NOTE: The functions in this class are "ported" from
+// https://github.com/donmccurdy/glTF-Transform/pull/1375/files
+//
+// The only exported function is "copyToDocument", which will be replaced
+// by the `copyToDocument` functionality of glTF-Transform 4.0
+
+import { Document } from "@gltf-transform/core";
+import { Graph } from "@gltf-transform/core";
+import { Property } from "@gltf-transform/core";
+import { PropertyType } from "@gltf-transform/core";
+import { PropertyResolver } from "@gltf-transform/core/dist/properties";
+
+const { TEXTURE_INFO, ROOT } = PropertyType;
+type PropertyConstructor = new (g: Graph<Property>) => Property;
+const NO_TRANSFER_TYPES = new Set<string>([TEXTURE_INFO, ROOT]);
+
+export function copyToDocument(
+  target: Document,
+  source: Document,
+  sourceProperties: Property[],
+  resolve?: PropertyResolver<Property>
+): Map<Property, Property> {
+  const sourcePropertyDependencies = new Set<Property>();
+  for (const property of sourceProperties) {
+    if (NO_TRANSFER_TYPES.has(property.propertyType)) {
+      throw new Error(`Type "${property.propertyType}" cannot be transferred.`);
+    }
+    listPropertyDependencies(property, sourcePropertyDependencies);
+  }
+  return _copyToDocument(
+    target,
+    source,
+    Array.from(sourcePropertyDependencies),
+    resolve
+  );
+}
+
+function _copyToDocument(
+  target: Document,
+  source: Document,
+  sourceProperties: Property[],
+  resolve?: PropertyResolver<Property>
+): Map<Property, Property> {
+  resolve ||= createDefaultPropertyResolver(target, source);
+
+  // Create stub classes for every Property in other Document.
+  const propertyMap = new Map<Property, Property>();
+  for (const sourceProp of sourceProperties) {
+    // TextureInfo copy handled by Material or ExtensionProperty.
+    if (
+      !propertyMap.has(sourceProp) &&
+      sourceProp.propertyType !== TEXTURE_INFO
+    ) {
+      propertyMap.set(sourceProp, resolve(sourceProp));
+    }
+  }
+
+  // Assemble relationships between Properties.
+  for (const [sourceProp, targetProp] of propertyMap.entries()) {
+    targetProp.copy(sourceProp, resolve);
+  }
+
+  return propertyMap;
+}
+
+function createDefaultPropertyResolver(
+  target: Document,
+  source: Document
+): PropertyResolver<Property> {
+  const propertyMap = new Map<Property, Property>([
+    [source.getRoot(), target.getRoot()],
+  ]);
+
+  return (sourceProp: Property): Property => {
+    // TextureInfo lifecycle is bound to a Material or ExtensionProperty.
+    if (sourceProp.propertyType === TEXTURE_INFO) return sourceProp;
+
+    let targetProp = propertyMap.get(sourceProp);
+    if (!targetProp) {
+      // Create stub class, defer copying properties.
+      const PropertyClass = sourceProp.constructor as PropertyConstructor;
+      targetProp = new PropertyClass(target.getGraph());
+      propertyMap.set(sourceProp, targetProp);
+    }
+
+    return targetProp;
+  };
+}
+
+function listPropertyDependencies(
+  parent: Property,
+  visited: Set<Property>
+): Set<Property> {
+  const graph = parent.getGraph();
+  const queue: Property[] = [parent];
+
+  let next: Property | undefined = undefined;
+  while ((next = queue.pop())) {
+    visited.add(next);
+    for (const child of graph.listChildren(next)) {
+      if (!visited.has(child)) {
+        queue.push(child);
+      }
+    }
+  }
+
+  return visited;
+}