glb2: Add Glb2Importer

Mostly copy/paste from Glb1Importer but it returns a different schema
version and uses the standard ".glb" file extension.

Change-Id: Id000b01593e8277a7e9cc5b4209aa7ebf8d7bd99

UnitySDK/Assets/TiltBrush/Scripts/Editor/Glb2Importer.cs

@@ -0,0 +1,72 @@
+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+
+using Object = UnityEngine.Object;
+#if UNITY_2017_1_OR_NEWER
+using System;
+using System.IO;
+
+using UnityEngine;
+using UnityEditor;
+using UnityEditor.Experimental.AssetImporters;
+
+namespace TiltBrushToolkit {
+
+[ScriptedImporter(kVersion, "glb", kImportQueueOffset)]
+public class Glb2Importer : ScriptedImporter {
+  const int kVersion = 2;
+  // ImportGltf needs to reference meshes and textures, so the glb import
+  // must come after them. We're assuming that Unity built-in asset types
+  // import at queue offset = 0.
+  const int kImportQueueOffset = 1;
+
+  private static readonly PolyImportOptions kOptions = new PolyImportOptions {
+      rescalingMode = PolyImportOptions.RescalingMode.CONVERT,
+      scaleFactor = 1,
+      recenter = false,
+  };
+
+  public override void OnImportAsset(AssetImportContext ctx) {
+    StringReader gltfStream = new StringReader(GlbParser.GetJsonChunkAsString(ctx.assetPath));
+    IUriLoader loader = new BufferedStreamLoader(
+        ctx.assetPath, Path.GetDirectoryName(ctx.assetPath));
+
+    ImportGltf.GltfImportResult result = ImportGltf.Import(
+        GltfSchemaVersion.GLTF2, gltfStream, loader, kOptions);
+
+    // The "identifier" param passed here is supposed to be:
+    // - Unique to this asset
+    // - Deterministic (if possible)
+    foreach (var obj in result.textures) {
+      if (! AssetDatabase.Contains(obj)) {
+        ctx.AddObjectToAsset("Texture/" + obj.name, obj);
+      }
+    }
+    foreach (var obj in result.materials) {
+      ctx.AddObjectToAsset("Material/" + obj.name, obj);
+    }
+    foreach (var obj in result.meshes) {
+      ctx.AddObjectToAsset("Mesh/" + obj.name, obj);
+    }
+    string objectName = Path.GetFileNameWithoutExtension(ctx.assetPath);
+    result.root.name = objectName;
+    ctx.AddObjectToAsset("ROOT", result.root);
+    ctx.SetMainObject(result.root);
+  }
+}
+
+}  // namespace TiltBrushToolkit
+
+#endif