fix: enable export of scenes with KTX2 compressed textures

packages/model-viewer/src/features/scene-graph.ts

@@ -16,6 +16,7 @@
 import {property} from 'lit/decorators.js';
 import {CanvasTexture, Object3D, RepeatWrapping, SRGBColorSpace, Texture, VideoTexture} from 'three';
 import {GLTFExporter, GLTFExporterOptions} from 'three/examples/jsm/exporters/GLTFExporter.js';
+import {decompress} from 'three/examples/jsm/utils/WebGLTextureUtils.js';
 
 import ModelViewerElementBase, {$needsRender, $onModelLoad, $progressTracker, $renderer, $scene} from '../model-viewer-base.js';
 import {GLTF} from '../three-components/gltf-instance/gltf-defaulted.js';
@@ -289,6 +290,13 @@ export const SceneGraphMixin = <T extends Constructor<ModelViewerElementBase>>(
                 .register(
                     (writer: any) =>
                         new GLTFExporterMaterialsVariantsExtension(writer));
+
+        exporter.setTextureUtils({
+          decompress: (texture: Texture, maxTextureSize?: number) => {
+            return decompress(texture, maxTextureSize ?? Infinity, undefined);
+          }
+        });
+
         let exportTarget: Object3D;
         if (scene.models.length > 1) {
           exportTarget = new Object3D();

packages/model-viewer/src/test/features/scene-graph/texture-spec.ts

@@ -75,6 +75,37 @@ suite('scene-graph/texture', () => {
           .to.be.equal('image/png');
     });
 
+    test(
+        'exports and re-imports a model with KTX2 compressed texture',
+        async () => {
+          const ktx2Texture = await element.createTexture(KTX2_TEXTURE_PATH);
+          element.model!.materials[0]
+              .pbrMetallicRoughness.baseColorTexture!.setTexture(ktx2Texture);
+
+          const materialCount = element.model!.materials.length;
+          const dim = element.getDimensions();
+
+          const exported = await element.exportScene({binary: true});
+          expect(exported).to.be.not.undefined;
+          expect(exported.size).to.be.greaterThan(500);
+
+          // Verify scene is still intact after export (no renderer
+          // corruption).
+          expect(element.model).to.not.be.null;
+          expect(element.model!.materials.length).to.equal(materialCount);
+          const dimAfter = element.getDimensions();
+          expect(dimAfter.x).to.be.closeTo(dim.x, 0.001);
+          expect(dimAfter.y).to.be.closeTo(dim.y, 0.001);
+          expect(dimAfter.z).to.be.closeTo(dim.z, 0.001);
+
+          const url = URL.createObjectURL(exported);
+          element.src = url;
+          await waitForEvent(element, 'load');
+
+          expect(element.model).to.not.be.null;
+          expect(element.model!.materials.length).to.be.greaterThan(0);
+        });
+
     test('Verify legacy correlatedObjects are updated.', async () => {
       const newUUID: string|undefined = texture?.source[$threeTexture]?.uuid;