Add support for loading asset directly from ImmutableBuffer (flutter/engine#32999)

engine/src/flutter/lib/ui/painting.dart

@@ -2053,6 +2053,48 @@ Future<Codec> instantiateImageCodec(
   bool allowUpscaling = true,
 }) async {
   final ImmutableBuffer buffer = await ImmutableBuffer.fromUint8List(list);
+  return instantiateImageCodecFromBuffer(
+    buffer,
+    targetWidth: targetWidth,
+    targetHeight: targetHeight,
+    allowUpscaling: allowUpscaling,
+  );
+}
+
+/// Instantiates an image [Codec].
+///
+/// This method is a convenience wrapper around the [ImageDescriptor] API, and
+/// using [ImageDescriptor] directly is preferred since it allows the caller to
+/// make better determinations about how and whether to use the `targetWidth`
+/// and `targetHeight` parameters.
+///
+/// The [buffer] parameter is the binary image data (e.g a PNG or GIF binary data).
+/// The data can be for either static or animated images. The following image
+/// formats are supported: {@macro dart.ui.imageFormats}
+///
+/// The [targetWidth] and [targetHeight] arguments specify the size of the
+/// output image, in image pixels. If they are not equal to the intrinsic
+/// dimensions of the image, then the image will be scaled after being decoded.
+/// If the `allowUpscaling` parameter is not set to true, both dimensions will
+/// be capped at the intrinsic dimensions of the image, even if only one of
+/// them would have exceeded those intrinsic dimensions. If exactly one of these
+/// two arguments is specified, then the aspect ratio will be maintained while
+/// forcing the image to match the other given dimension. If neither is
+/// specified, then the image maintains its intrinsic size.
+///
+/// Scaling the image to larger than its intrinsic size should usually be
+/// avoided, since it causes the image to use more memory than necessary.
+/// Instead, prefer scaling the [Canvas] transform. If the image must be scaled
+/// up, the `allowUpscaling` parameter must be set to true.
+///
+/// The returned future can complete with an error if the image decoding has
+/// failed.
+Future<Codec> instantiateImageCodecFromBuffer(
+  ImmutableBuffer buffer, {
+  int? targetWidth,
+  int? targetHeight,
+  bool allowUpscaling = true,
+}) async {
   final ImageDescriptor descriptor = await ImageDescriptor.encoded(buffer);
   if (!allowUpscaling) {
     if (targetWidth != null && targetWidth > descriptor.width) {
@@ -5511,7 +5553,7 @@ class Shadow {
 /// The creator of this object is responsible for calling [dispose] when it is
 /// no longer needed.
 class ImmutableBuffer extends NativeFieldWrapperClass1 {
-  ImmutableBuffer._(this.length);
+  ImmutableBuffer._(this._length);
 
   /// Creates a copy of the data from a [Uint8List] suitable for internal use
   /// in the engine.
@@ -5521,10 +5563,24 @@ class ImmutableBuffer extends NativeFieldWrapperClass1 {
       instance._init(list, callback);
     }).then((_) => instance);
   }
+
+  /// Create a buffer from the asset with key [assetKey].
+  ///
+  /// Throws an [Exception] if the asset does not exist.
+  static Future<ImmutableBuffer> fromAsset(String assetKey) {
+    final ImmutableBuffer instance = ImmutableBuffer._(0);
+    return _futurize((_Callback<int> callback) {
+      return instance._initFromAsset(assetKey, callback);
+    }).then((int length) => instance.._length = length);
+  }
+
   void _init(Uint8List list, _Callback<void> callback) native 'ImmutableBuffer_init';
 
+  String? _initFromAsset(String assetKey, _Callback<int> callback) native 'ImmutableBuffer_initFromAsset';
+
   /// The length, in bytes, of the underlying data.
-  final int length;
+  int get length => _length;
+  int _length;
 
   bool _debugDisposed = false;
 

engine/src/flutter/lib/ui/painting/immutable_buffer.cc

@@ -7,6 +7,7 @@
 #include <cstring>
 
 #include "flutter/lib/ui/ui_dart_state.h"
+#include "flutter/lib/ui/window/platform_configuration.h"
 #include "third_party/tonic/converter/dart_converter.h"
 #include "third_party/tonic/dart_args.h"
 #include "third_party/tonic/dart_binding_macros.h"
@@ -30,6 +31,9 @@ ImmutableBuffer::~ImmutableBuffer() {}
 void ImmutableBuffer::RegisterNatives(tonic::DartLibraryNatives* natives) {
   natives->Register({{"ImmutableBuffer_init", ImmutableBuffer::init, 3, true},
                      FOR_EACH_BINDING(DART_REGISTER_NATIVE)});
+  natives->Register({{"ImmutableBuffer_initFromAsset",
+                      ImmutableBuffer::initFromAsset, 3, true},
+                     FOR_EACH_BINDING(DART_REGISTER_NATIVE)});
 }
 
 void ImmutableBuffer::init(Dart_NativeArguments args) {
@@ -49,6 +53,45 @@ void ImmutableBuffer::init(Dart_NativeArguments args) {
   tonic::DartInvoke(callback_handle, {Dart_TypeVoid()});
 }
 
+void ImmutableBuffer::initFromAsset(Dart_NativeArguments args) {
+  UIDartState::ThrowIfUIOperationsProhibited();
+  Dart_Handle callback_handle = Dart_GetNativeArgument(args, 2);
+  if (!Dart_IsClosure(callback_handle)) {
+    Dart_SetReturnValue(args, tonic::ToDart("Callback must be a function"));
+    return;
+  }
+  Dart_Handle asset_name_handle = Dart_GetNativeArgument(args, 1);
+  uint8_t* chars = nullptr;
+  intptr_t asset_length = 0;
+  Dart_Handle result =
+      Dart_StringToUTF8(asset_name_handle, &chars, &asset_length);
+  if (Dart_IsError(result)) {
+    Dart_SetReturnValue(args, tonic::ToDart("Asset must be valid UTF8"));
+    return;
+  }
+  Dart_Handle immutable_buffer = Dart_GetNativeArgument(args, 0);
+
+  std::string asset_name = std::string{reinterpret_cast<const char*>(chars),
+                                       static_cast<size_t>(asset_length)};
+
+  std::shared_ptr<AssetManager> asset_manager = UIDartState::Current()
+                                                    ->platform_configuration()
+                                                    ->client()
+                                                    ->GetAssetManager();
+  std::unique_ptr<fml::Mapping> data = asset_manager->GetAsMapping(asset_name);
+  if (data == nullptr) {
+    Dart_SetReturnValue(args, tonic::ToDart("Asset not found"));
+    return;
+  }
+
+  auto size = data->GetSize();
+  const void* bytes = static_cast<const void*>(data->GetMapping());
+  auto sk_data = MakeSkDataWithCopy(bytes, size);
+  auto buffer = fml::MakeRefCounted<ImmutableBuffer>(sk_data);
+  buffer->AssociateWithDartWrapper(immutable_buffer);
+  tonic::DartInvoke(callback_handle, {tonic::ToDart(size)});
+}
+
 size_t ImmutableBuffer::GetAllocationSize() const {
   return sizeof(ImmutableBuffer) + data_->size();
 }

engine/src/flutter/lib/ui/painting/immutable_buffer.h

@@ -39,6 +39,19 @@ class ImmutableBuffer : public RefCountedDartWrappable<ImmutableBuffer> {
   /// when the copy has completed.
   static void init(Dart_NativeArguments args);
 
+  /// Initializes a new ImmutableData from an asset matching a provided
+  /// asset string.
+  ///
+  /// The zero indexed argument is the caller that will be registered as the
+  /// Dart peer of the native ImmutableBuffer object.
+  ///
+  /// The first indexed argumented is a String corresponding to the asset
+  /// to load.
+  ///
+  /// The second indexed argument is expected to be a void callback to signal
+  /// when the copy has completed.
+  static void initFromAsset(Dart_NativeArguments args);
+
   /// The length of the data in bytes.
   size_t length() const {
     FML_DCHECK(data_);

engine/src/flutter/lib/ui/window/platform_configuration.h

@@ -11,6 +11,7 @@
 #include <unordered_map>
 #include <vector>
 
+#include "flutter/assets/asset_manager.h"
 #include "flutter/fml/time/time_point.h"
 #include "flutter/lib/ui/semantics/semantics_update.h"
 #include "flutter/lib/ui/window/pointer_data_packet.h"
@@ -98,6 +99,11 @@ class PlatformConfigurationClient {
   ///             creation.
   virtual FontCollection& GetFontCollection() = 0;
 
+  //--------------------------------------------------------------------------
+  /// @brief      Returns the current collection of assets available on the
+  ///             platform.
+  virtual std::shared_ptr<AssetManager> GetAssetManager() = 0;
+
   //--------------------------------------------------------------------------
   /// @brief      Notifies this client of the name of the root isolate and its
   ///             port when that isolate is launched, restarted (in the

engine/src/flutter/lib/web_ui/lib/painting.dart

@@ -484,6 +484,20 @@ Future<Codec> instantiateImageCodec(
   }
 }
 
+Future<Codec> instantiateImageCodecFromBuffer(
+  ImmutableBuffer buffer, {
+  int? targetWidth,
+  int? targetHeight,
+  bool allowUpscaling = true,
+}) async {
+  if (engine.useCanvasKit) {
+    return engine.skiaInstantiateImageCodec(buffer._list!, targetWidth, targetHeight);
+  } else {
+    final html.Blob blob = html.Blob(<dynamic>[buffer._list!.buffer]);
+    return engine.HtmlBlobCodec(blob);
+  }
+}
+
 Future<Codec> webOnlyInstantiateImageCodecFromUrl(Uri uri,
   {engine.WebOnlyImageCodecChunkCallback? chunkCallback}) {
   if (engine.useCanvasKit) {
@@ -735,15 +749,21 @@ class ImageShader extends Shader {
 }
 
 class ImmutableBuffer {
-  ImmutableBuffer._(this.length);
+  ImmutableBuffer._(this._length);
   static Future<ImmutableBuffer> fromUint8List(Uint8List list) async {
     final ImmutableBuffer instance = ImmutableBuffer._(list.length);
     instance._list = list;
     return instance;
   }
 
+  static Future<ImmutableBuffer> fromAsset(String assetKey) async {
+    throw UnsupportedError('ImmutableBuffer.fromAsset is not supported on the web.');
+  }
+
   Uint8List? _list;
-  final int length;
+
+  int get length => _length;
+  int _length;
 
   bool get debugDisposed {
     late bool disposed;

engine/src/flutter/runtime/runtime_controller.cc

@@ -299,6 +299,11 @@ FontCollection& RuntimeController::GetFontCollection() {
   return client_.GetFontCollection();
 }
 
+// |PlatfromConfigurationClient|
+std::shared_ptr<AssetManager> RuntimeController::GetAssetManager() {
+  return client_.GetAssetManager();
+}
+
 // |PlatformConfigurationClient|
 void RuntimeController::UpdateIsolateDescription(const std::string isolate_name,
                                                  int64_t isolate_port) {

engine/src/flutter/runtime/runtime_controller.h

@@ -8,6 +8,7 @@
 #include <memory>
 #include <vector>
 
+#include "flutter/assets/asset_manager.h"
 #include "flutter/common/task_runners.h"
 #include "flutter/flow/layers/layer_tree.h"
 #include "flutter/fml/macros.h"
@@ -614,6 +615,9 @@ class RuntimeController : public PlatformConfigurationClient {
   // |PlatformConfigurationClient|
   FontCollection& GetFontCollection() override;
 
+  // |PlatformConfigurationClient|
+  std::shared_ptr<AssetManager> GetAssetManager() override;
+
   // |PlatformConfigurationClient|
   void UpdateIsolateDescription(const std::string isolate_name,
                                 int64_t isolate_port) override;

engine/src/flutter/runtime/runtime_delegate.h

@@ -8,6 +8,7 @@
 #include <memory>
 #include <vector>
 
+#include "flutter/assets/asset_manager.h"
 #include "flutter/flow/layers/layer_tree.h"
 #include "flutter/lib/ui/semantics/custom_accessibility_action.h"
 #include "flutter/lib/ui/semantics/semantics_node.h"
@@ -33,6 +34,8 @@ class RuntimeDelegate {
 
   virtual FontCollection& GetFontCollection() = 0;
 
+  virtual std::shared_ptr<AssetManager> GetAssetManager() = 0;
+
   virtual void OnRootIsolateCreated() = 0;
 
   virtual void UpdateIsolateDescription(const std::string isolate_name,

engine/src/flutter/shell/common/engine.h

@@ -755,8 +755,8 @@ class Engine final : public RuntimeDelegate, PointerDataDispatcher::Delegate {
   // |RuntimeDelegate|
   FontCollection& GetFontCollection() override;
 
-  // Return the asset manager associated with the current engine, or nullptr.
-  std::shared_ptr<AssetManager> GetAssetManager();
+  // |RuntimeDelegate|
+  std::shared_ptr<AssetManager> GetAssetManager() override;
 
   // Return the weak_ptr of ImageDecoder.
   fml::WeakPtr<ImageDecoder> GetImageDecoderWeakPtr();

engine/src/flutter/shell/common/engine_unittests.cc

@@ -53,6 +53,7 @@ class MockRuntimeDelegate : public RuntimeDelegate {
                void(SemanticsNodeUpdates, CustomAccessibilityActionUpdates));
   MOCK_METHOD1(HandlePlatformMessage, void(std::unique_ptr<PlatformMessage>));
   MOCK_METHOD0(GetFontCollection, FontCollection&());
+  MOCK_METHOD0(GetAssetManager, std::shared_ptr<AssetManager>());
   MOCK_METHOD0(OnRootIsolateCreated, void());
   MOCK_METHOD2(UpdateIsolateDescription, void(const std::string, int64_t));
   MOCK_METHOD1(SetNeedsReportTimings, void(bool));

engine/src/flutter/testing/dart/BUILD.gn

@@ -5,6 +5,7 @@
 import("//flutter/testing/dart/compile_test.gni")
 
 tests = [
+  "assets_test.dart",
   "canvas_test.dart",
   "channel_buffers_test.dart",
   "codec_test.dart",

engine/src/flutter/testing/dart/assets_test.dart

@@ -0,0 +1,32 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:ui' as ui;
+
+import 'package:litetest/litetest.dart';
+
+void main() {
+  test('Loading an asset that does not exist returns null', () async {
+    Object? error;
+    try {
+      await ui.ImmutableBuffer.fromAsset('ThisDoesNotExist');
+    } catch (err) {
+      error = err;
+    }
+    expect(error, isNotNull);
+    expect(error is Exception, true);
+  });
+
+  test('returns the bytes of a bundled asset', () async {
+    final ui.ImmutableBuffer buffer = await ui.ImmutableBuffer.fromAsset('assets/DashInNooglerHat.jpg');
+
+    expect(buffer.length == 354679, true);
+  });
+
+  test('can dispose immutable buffer', () async {
+    final ui.ImmutableBuffer buffer = await ui.ImmutableBuffer.fromAsset('assets/DashInNooglerHat.jpg');
+
+    buffer.dispose();
+  });
+}

engine/src/flutter/testing/run_tests.py

@@ -286,6 +286,7 @@ def RunDartTest(build_dir, test_packages, dart_file, verbose_dart_snapshot, mult
   command_args += [
     '--use-test-fonts',
     '--icu-data-file-path=%s' % os.path.join(build_dir, 'icudtl.dat'),
+    '--flutter-assets-dir=%s' % os.path.join(build_dir, 'gen', 'flutter', 'lib', 'ui'),
     kernel_file_output,
   ]