fix: apply URDF material to child meshes when loadMeshCb returns a Group

javascript/src/URDFLoader.js

@@ -586,11 +586,15 @@ class URDFLoader {
 
                                 } else if (obj) {
 
-                                    if (obj instanceof THREE.Mesh) {
+                                    obj.traverse(child => {
 
-                                        obj.material = material;
+                                        if (child instanceof THREE.Mesh) {
 
-                                    }
+                                            child.material = material;
+
+                                        }
+
+                                    });
 
                                     // We don't expect non identity rotations or positions. In the case of
                                     // COLLADA files the model might come in with a custom scale for unit

javascript/test/URDFLoader.test.js

@@ -1,5 +1,5 @@
 import { JSDOM } from 'jsdom';
-import { Mesh, Color } from 'three';
+import { Mesh, Group, Color } from 'three';
 import fetch from 'node-fetch';
 import URDFLoader from '../src/URDFLoader.js';
 
@@ -432,6 +432,50 @@ describe('Material Tags', () => {
 
     });
 
+    it('should apply URDF material to child meshes when loadMeshCb returns a Group.', () => {
+
+        const loader = new URDFLoader();
+        loader.loadMeshCb = (path, manager, done) => {
+
+            const group = new Group();
+            group.add(new Mesh());
+            group.add(new Mesh());
+            done(group);
+
+        };
+
+        const res = loader.parse(`
+            <robot name="TEST">
+                <material name="Cyan">
+                    <color rgba="0 1.0 1.0 1.0"/>
+                </material>
+                <link name="LINK">
+                    <visual>
+                        <geometry>
+                            <mesh filename="package://meshes/link.obj" />
+                        </geometry>
+                        <material name="Cyan"/>
+                    </visual>
+                </link>
+            </robot>
+        `);
+
+        const visual = res.children[0].children[0];
+        const group = visual.children[0];
+
+        group.traverse(child => {
+
+            if (child instanceof Mesh) {
+
+                expect(child.material.name).toEqual('Cyan');
+                expect(child.material.color).toEqual(new Color(0, 1, 1).convertSRGBToLinear());
+
+            }
+
+        });
+
+    });
+
     it('should parse transparent materials correctly.', () => {
 
         const loader = new URDFLoader();