Enable Image encoding by leveraging existing Skia functionality

lib/ui/BUILD.gn

@@ -24,6 +24,8 @@ source_set("ui") {
     "painting/gradient.h",
     "painting/image.cc",
     "painting/image.h",
+    "painting/image_encoding.cc",
+    "painting/image_encoding.h",
     "painting/image_filter.cc",
     "painting/image_filter.h",
     "painting/image_shader.cc",

lib/ui/painting.dart

@@ -1196,6 +1196,80 @@ class Paint {
   }
 }
 
+/// An encoding format to use with the [Image.toByteData].
+class EncodingFormat {
+  final int _format;
+  final int _quality;
+
+  // Be conservative with the formats we expose. It is easy to add new formats
+  // in future but difficult to remove.
+  // These values must be kept in sync with the logic in ToSkEncodedImageFormat.
+  static const int _jpegFormat = 0;
+  static const int _pngFormat = 1;
+  static const int _webpFormat = 2;
+
+  /// PNG format.
+  ///
+  /// A loss-less compression format for images. This format is well suited for
+  /// images with hard edges, such as screenshots or sprites, and images with
+  /// text. Transparency is supported. The PNG format supports images up to
+  /// 2,147,483,647 pixels in either dimension, though in practice available
+  /// memory provides a more immediate limitation on maximum image size.
+  ///
+  /// PNG images normally use the `.png` file extension and the `image/png` MIME
+  /// type.
+  ///
+  /// See also:
+  ///
+  ///  * <https://en.wikipedia.org/wiki/Portable_Network_Graphics>, the Wikipedia page on PNG.
+  ///  * <https://tools.ietf.org/rfc/rfc2083.txt>, the PNG standard.
+  const EncodingFormat.png()
+      : _format = _pngFormat,
+        _quality = 0;
+
+  /// JPEG format.
+  ///
+  /// This format, strictly speaking called JFIF, is a lossy compression
+  /// graphics format that can handle images up to 65,535 pixels in either
+  /// dimension. The [quality] metric is a value in the range 0 to 100 that
+  /// controls the compression ratio. Values in the range of about 50 to 90 are
+  /// somewhat reasonable; values above 95 increase the file size with little
+  /// noticeable improvement to the quality, values below 50 drop the quality
+  /// substantially.
+  ///
+  /// This format is well suited for photographs. It is very poorly suited for
+  /// images with hard edges or text. It does not support transparency.
+  ///
+  /// JPEG images normally use the `.jpeg` file extension and the `image/jpeg`
+  /// MIME type.
+  ///
+  /// See also:
+  ///
+  ///  * <https://en.wikipedia.org/wiki/JPEG>, the Wikipedia page on JPEG.
+  const EncodingFormat.jpeg({int quality = 80})
+      : _format = _jpegFormat,
+        _quality = quality;
+
+  /// WebP format.
+  ///
+  /// The WebP format supports both lossy and lossless compression; however, the
+  /// [Image.toByteData] method always uses lossy compression when [webp] is
+  /// specified. The [quality] metric is a value in the range 0 to 100 that
+  /// controls the compression ratio; higher values result in better quality but
+  /// larger file sizes, and vice versa. WebP images are limited to 16,383
+  /// pixels in each direction (width and height).
+  ///
+  /// WebP images normally use the `.webp` file extension and the `image/webp`
+  /// MIME type.
+  ///
+  /// See also:
+  ///
+  ///  * <https://en.wikipedia.org/wiki/WebP>, the Wikipedia page on WebP.
+  const EncodingFormat.webp({int quality = 80})
+      : _format = _webpFormat,
+        _quality = quality;
+}
+
 /// Opaque handle to raw decoded image data (pixels).
 ///
 /// To obtain an [Image] object, use [instantiateImageCodec].
@@ -1215,6 +1289,21 @@ class Image extends NativeFieldWrapperClass2 {
   /// The number of image pixels along the image's vertical axis.
   int get height native 'Image_height';
 
+  /// Converts the [Image] object into a byte array.
+  ///
+  /// The [format] is encoding format to be used.
+  ///
+  /// Returns a future which complete with the binary image data (e.g a PNG or JPEG binary data) or
+  /// an error if encoding fails.
+  Future<Uint8List> toByteData({EncodingFormat format: const EncodingFormat.jpeg()}) {
+    return _futurize(
+          (_Callback<Uint8List> callback) => _toByteData(format._format, format._quality, callback)
+    );
+  }
+
+  /// Returns an error message on failure, null on success.
+  String _toByteData(int format, int quality, _Callback<Uint8List> callback) native 'Image_toByteData';
+
   /// Release the resources used by this object. The object is no longer usable
   /// after this method is called.
   void dispose() native 'Image_dispose';

lib/ui/painting/image.cc

@@ -5,6 +5,7 @@
 #include "flutter/lib/ui/painting/image.h"
 
 #include "flutter/common/threads.h"
+#include "flutter/lib/ui/painting/image_encoding.h"
 #include "flutter/lib/ui/painting/utils.h"
 #include "lib/tonic/converter/dart_converter.h"
 #include "lib/tonic/dart_args.h"
@@ -20,6 +21,7 @@ IMPLEMENT_WRAPPERTYPEINFO(ui, Image);
 #define FOR_EACH_BINDING(V) \
   V(Image, width)           \
   V(Image, height)          \
+  V(Image, toByteData)      \
   V(Image, dispose)
 
 FOR_EACH_BINDING(DART_NATIVE_CALLBACK)
@@ -36,6 +38,12 @@ CanvasImage::~CanvasImage() {
   SkiaUnrefOnIOThread(&image_);
 }
 
+Dart_Handle CanvasImage::toByteData(int format,
+                                    int quality,
+                                    Dart_Handle callback) {
+  return EncodeImage(this, format, quality, callback);
+}
+
 void CanvasImage::dispose() {
   ClearDartWrapper();
 }

lib/ui/painting/image.h

@@ -27,6 +27,7 @@ class CanvasImage final : public fxl::RefCountedThreadSafe<CanvasImage>,
 
   int width() { return image_->width(); }
   int height() { return image_->height(); }
+  Dart_Handle toByteData(int format, int quality, Dart_Handle callback);
   void dispose();
 
   const sk_sp<SkImage>& image() const { return image_; }

lib/ui/painting/image_encoding.cc

@@ -0,0 +1,113 @@
+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/lib/ui/painting/image_encoding.h"
+
+#include "flutter/common/threads.h"
+#include "flutter/lib/ui/painting/image.h"
+#include "flutter/lib/ui/painting/resource_context.h"
+#include "lib/fxl/build_config.h"
+#include "lib/fxl/functional/make_copyable.h"
+#include "lib/tonic/dart_persistent_value.h"
+#include "lib/tonic/dart_state.h"
+#include "lib/tonic/logging/dart_invoke.h"
+#include "lib/tonic/typed_data/uint8_list.h"
+#include "third_party/skia/include/core/SkEncodedImageFormat.h"
+#include "third_party/skia/include/core/SkImage.h"
+
+using tonic::DartInvoke;
+using tonic::DartPersistentValue;
+using tonic::ToDart;
+
+namespace blink {
+namespace {
+
+void InvokeDataCallback(std::unique_ptr<DartPersistentValue> callback,
+                        sk_sp<SkData> buffer) {
+  tonic::DartState* dart_state = callback->dart_state().get();
+  if (!dart_state) {
+    return;
+  }
+  tonic::DartState::Scope scope(dart_state);
+  if (!buffer) {
+    DartInvoke(callback->value(), {Dart_Null()});
+  } else {
+    Dart_Handle dart_data = tonic::DartConverter<tonic::Uint8List>::ToDart(
+        buffer->bytes(), buffer->size());
+    DartInvoke(callback->value(), {dart_data});
+  }
+}
+
+sk_sp<SkData> EncodeImage(sk_sp<SkImage> image,
+                          SkEncodedImageFormat format,
+                          int quality) {
+  if (image == nullptr) {
+    return nullptr;
+  }
+  return image->encodeToData(format, quality);
+}
+
+void EncodeImageAndInvokeDataCallback(
+    std::unique_ptr<DartPersistentValue> callback,
+    sk_sp<SkImage> image,
+    SkEncodedImageFormat format,
+    int quality) {
+  sk_sp<SkData> encoded = EncodeImage(std::move(image), format, quality);
+
+  Threads::UI()->PostTask(
+      fxl::MakeCopyable([callback = std::move(callback), encoded]() mutable {
+        InvokeDataCallback(std::move(callback), std::move(encoded));
+      }));
+}
+
+SkEncodedImageFormat ToSkEncodedImageFormat(int format) {
+  // Map the formats exposed in flutter to formats supported in Skia.
+  // See:
+  // https://github.com/google/skia/blob/master/include/core/SkEncodedImageFormat.h
+  switch (format) {
+    case 0:
+      return SkEncodedImageFormat::kJPEG;
+    case 1:
+      return SkEncodedImageFormat::kPNG;
+    case 2:
+      return SkEncodedImageFormat::kWEBP;
+    default:
+      /* NOTREACHED */
+      return SkEncodedImageFormat::kWEBP;
+  }
+}
+
+}  // namespace
+
+Dart_Handle EncodeImage(CanvasImage* canvas_image,
+                        int format,
+                        int quality,
+                        Dart_Handle callback_handle) {
+  if (!canvas_image)
+    return ToDart("encode called with non-genuine Image.");
+
+  if (!Dart_IsClosure(callback_handle))
+    return ToDart("Callback must be a function.");
+
+  SkEncodedImageFormat image_format = ToSkEncodedImageFormat(format);
+
+  if (quality > 100)
+    quality = 100;
+  if (quality < 0)
+    quality = 0;
+
+  auto callback = std::make_unique<DartPersistentValue>(
+      tonic::DartState::Current(), callback_handle);
+  sk_sp<SkImage> image = canvas_image->image();
+
+  Threads::IO()->PostTask(fxl::MakeCopyable(
+      [callback = std::move(callback), image, image_format, quality]() mutable {
+        EncodeImageAndInvokeDataCallback(std::move(callback), std::move(image),
+                                         image_format, quality);
+      }));
+
+  return Dart_Null();
+}
+
+}  // namespace blink

lib/ui/painting/image_encoding.h

@@ -0,0 +1,21 @@
+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FLUTTER_LIB_UI_PAINTING_IMAGE_ENCODING_H_
+#define FLUTTER_LIB_UI_PAINTING_IMAGE_ENCODING_H_
+
+#include "lib/tonic/dart_library_natives.h"
+
+namespace blink {
+
+class CanvasImage;
+
+Dart_Handle EncodeImage(CanvasImage* canvas_image,
+                        int format,
+                        int quality,
+                        Dart_Handle callback_handle);
+
+}  // namespace blink
+
+#endif  // FLUTTER_LIB_UI_PAINTING_IMAGE_ENCODING_H_

testing/dart/encoding_test.dart

@@ -0,0 +1,63 @@
+// Copyright 2018 The Chromium 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:async';
+import 'dart:ui';
+import 'dart:typed_data';
+import 'dart:io';
+
+import 'package:test/test.dart';
+import 'package:path/path.dart' as path;
+
+void main() {
+  final Image testImage = createSquareTestImage();
+
+  test('Encode with default arguments', () async {
+    Uint8List data = await testImage.toByteData();
+    Uint8List expected = readFile('square-80.jpg');
+    expect(data, expected);
+  });
+
+  test('Encode JPEG', () async {
+    Uint8List data = await testImage.toByteData(
+        format: new EncodingFormat.jpeg(quality: 80));
+    Uint8List expected = readFile('square-80.jpg');
+    expect(data, expected);
+  });
+
+  test('Encode PNG', () async {
+    Uint8List data =
+        await testImage.toByteData(format: new EncodingFormat.png());
+    Uint8List expected = readFile('square.png');
+    expect(data, expected);
+  });
+
+  test('Encode WEBP', () async {
+    Uint8List data = await testImage.toByteData(
+        format: new EncodingFormat.webp(quality: 80));
+    Uint8List expected = readFile('square-80.webp');
+    expect(data, expected);
+  });
+}
+
+Image createSquareTestImage() {
+  PictureRecorder recorder = new PictureRecorder();
+  Canvas canvas = new Canvas(recorder, new Rect.fromLTWH(0.0, 0.0, 10.0, 10.0));
+
+  Paint black = new Paint()
+    ..strokeWidth = 1.0
+    ..color = const Color.fromRGBO(0, 0, 0, 1.0);
+  Paint green = new Paint()
+    ..strokeWidth = 1.0
+    ..color = const Color.fromRGBO(0, 255, 0, 1.0);
+
+  canvas.drawRect(new Rect.fromLTWH(0.0, 0.0, 10.0, 10.0), black);
+  canvas.drawRect(new Rect.fromLTWH(2.0, 2.0, 6.0, 6.0), green);
+  return recorder.endRecording().toImage(10, 10);
+}
+
+Uint8List readFile(fileName) {
+  final file = new File(path.join('flutter', 'testing', 'resources', fileName));
+  return file.readAsBytesSync();
+}

travis/licenses_golden/licenses_flutter

@@ -1642,6 +1642,8 @@ ORIGIN: ../../../flutter/assets/asset_provider.h + ../../../LICENSE
 TYPE: LicenseType.bsd
 FILE: ../../../flutter/assets/asset_provider.h
 FILE: ../../../flutter/flutter_kernel_transformers/lib/track_widget_constructor_locations.dart
+FILE: ../../../flutter/lib/ui/painting/image_encoding.cc
+FILE: ../../../flutter/lib/ui/painting/image_encoding.h
 FILE: ../../../flutter/shell/platform/android/apk_asset_provider.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/accessibility_text_entry.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/accessibility_text_entry.mm