Add new async method to ModelViewer.

If you now try loading Bistro, the skybox shows up fairly quickly.
This works by moving AssetManager uncompression off the UI thread.

RELEASE_NOTES.md

@@ -6,8 +6,9 @@ A new header is inserted each time a *tag* is created.
 ## Next release
 
 - gltfio now supports simple instancing of entire assets.
-- For improved performance, gltfio now threads more tasks and assumes assets are well-formed.
+- gltfio has improved performance and assumes assets are well-formed.
 - gltfio now supports name and prefix lookup for entities.
+- ModelViewer now allows resources to be fetched off the UI thread.
 - Add missing JavaScript API for `View::setVisibleLayers()`.
 - Add support for DOF with Metal backend.
 - SSAO now has an optional high(er) quality upsampler.

android/filament-utils-android/src/main/java/com/google/android/filament/utils/ModelViewer.kt

@@ -16,6 +16,7 @@
 
 package com.google.android.filament.utils
 
+import android.os.AsyncTask
 import android.view.MotionEvent
 import android.view.Surface
 import android.view.SurfaceView
@@ -162,6 +163,8 @@ class ModelViewer(val engine: Engine) : android.view.View.OnTouchListener {
 
     /**
      * Loads a JSON-style glTF file and populates the Filament scene.
+     *
+     * The given callback is triggered for each requested resource.
      */
     fun loadModelGltf(buffer: Buffer, callback: (String) -> Buffer) {
         destroyModel()
@@ -176,6 +179,17 @@ class ModelViewer(val engine: Engine) : android.view.View.OnTouchListener {
         }
     }
 
+    /**
+     * Loads a JSON-style glTF file and populates the Filament scene.
+     *
+     * The given callback is triggered from a worker thread for each requested resource.
+     */
+    fun loadModelGltfAsync(buffer: Buffer, callback: (String) -> Buffer): ResourceTask {
+        destroyModel()
+        asset = assetLoader.createAssetFromJson(buffer)
+        return ReadAssetsTask(this, callback).execute()
+    }
+
     /**
      * Sets up a root transform on the current model to make it fit into a unit cube.
      *
@@ -281,6 +295,28 @@ class ModelViewer(val engine: Engine) : android.view.View.OnTouchListener {
         return true
     }
 
+    class ReadAssetsTask(val viewer: ModelViewer, val callback: (String) -> Buffer) : ResourceTask() {
+        override fun doInBackground(vararg params: Unit?): Map<String, Buffer> {
+            val items = HashMap<String, Buffer>()
+            val resourceUris = viewer.asset!!.resourceUris
+            for (resourceUri in resourceUris) {
+                items[resourceUri] = callback(resourceUri)
+            }
+            return items
+        }
+
+        override fun onPostExecute(result: Map<String, Buffer>) {
+            for ((uri, buffer) in result) {
+                viewer.resourceLoader.addResourceData(uri, buffer)
+            }
+            viewer.asset?.let { asset ->
+                viewer.resourceLoader.asyncBeginLoad(asset)
+                viewer.animator = asset.animator
+                asset.releaseSourceData()
+            }
+        }
+    }
+
     inner class SurfaceCallback : UiHelper.RendererCallback {
         override fun onNativeWindowChanged(surface: Surface) {
             swapChain?.let { engine.destroySwapChain(it) }
@@ -310,3 +346,5 @@ class ModelViewer(val engine: Engine) : android.view.View.OnTouchListener {
         private val kDefaultObjectPosition = Float3(0.0f, 0.0f, -4.0f)
     }
 }
+
+typealias ResourceTask = AsyncTask<Unit, Unit, Map<String, Buffer>>

android/samples/sample-gltf-viewer/src/main/java/com/google/android/filament/gltf/MainActivity.kt

@@ -80,9 +80,8 @@ class MainActivity : Activity() {
             input.read(bytes)
             ByteBuffer.wrap(bytes)
         }
-        modelViewer.loadModelGltf(buffer) { uri ->
-            readCompressedAsset("models/$uri")
-        }
+
+        modelViewer.loadModelGltfAsync(buffer, { uri -> readCompressedAsset("models/$uri") })
         modelViewer.transformToUnitCube()
     }