Add support for linear gradients, implemented as skia shaders.

I had to complicate the IDL bindings generation to allow passing an array of
colors. Without these changes, we'd try to convert the dart object to
Vector<SkColor>, which C++ thinks is Vector<unsigned>, and we'd use the wrong
converter. So I added some template grease to force it to use a
Vector<CanvasColor> converter.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1152963009

engine/bindings/scripts/dart_types.py

@@ -366,13 +366,12 @@ DART_TO_CPP_VALUE = {
     # Pass-by-value types.
     'Color': pass_by_value_format('CanvasColor'),
     'Float32List': pass_by_value_format('Float32List'),
-    'Point': pass_by_value_format('{implemented_as}'),
-    'Rect': pass_by_value_format('{implemented_as}'),
+    'Point': pass_by_value_format('Point'),
+    'Rect': pass_by_value_format('Rect'),
     'TransferMode': pass_by_value_format('TransferMode'),
     'PaintingStyle': pass_by_value_format('PaintingStyle'),
 }
 
-
 def dart_value_to_cpp_value(idl_type, extended_attributes, variable_name,
                             null_check, has_type_checking_interface,
                             index, auto_scope=True):
@@ -428,12 +427,19 @@ def dart_value_to_cpp_value(idl_type, extended_attributes, variable_name,
                                         auto_scope=DartUtilities.bool_to_cpp(auto_scope))
 
 
+# Special mappings for arrays of types.
+INNER_TYPE_FOR_ARRAY = {
+    'SkColor': 'CanvasColor'
+}
+
 def dart_value_to_cpp_value_array_or_sequence(native_array_element_type, variable_name, index):
     # Index is None for setters, index (starting at 0) for method arguments,
     # and is used to provide a human-readable exception message
     if index is None:
         index = 0  # special case, meaning "setter"
     this_cpp_type = native_array_element_type.cpp_type
+    if this_cpp_type in INNER_TYPE_FOR_ARRAY:
+      this_cpp_type = INNER_TYPE_FOR_ARRAY[this_cpp_type]
     expression_format = '{variable_name} = DartConverter<Vector<{cpp_type}>>::FromArguments(args, {index}, exception)'
     expression = expression_format.format(native_array_element_type=native_array_element_type.name,
                                           cpp_type=this_cpp_type, index=index,

engine/core/core.gni

@@ -852,6 +852,8 @@ sky_core_files = [
   "painting/DrawLooperAddLayerCallback.h",
   "painting/DrawLooperLayerInfo.cpp",
   "painting/DrawLooperLayerInfo.h",
+  "painting/CanvasGradient.cpp",
+  "painting/CanvasGradient.h",
   "painting/LayerDrawLooperBuilder.cpp",
   "painting/LayerDrawLooperBuilder.h",
   "painting/LayoutRoot.cpp",
@@ -878,6 +880,8 @@ sky_core_files = [
   "painting/Rect.h",
   "painting/RRect.cpp",
   "painting/RRect.h",
+  "painting/Shader.cpp",
+  "painting/Shader.h",
   "painting/TransferMode.cpp",
   "painting/TransferMode.h",
   "rendering/BidiRun.h",
@@ -1145,6 +1149,7 @@ core_idl_files = get_path_info([
                                  "painting/DrawLooper.idl",
                                  "painting/DrawLooperAddLayerCallback.idl",
                                  "painting/DrawLooperLayerInfo.idl",
+                                 "painting/Gradient.idl",
                                  "painting/Image.idl",
                                  "painting/LayerDrawLooperBuilder.idl",
                                  "painting/LayoutRoot.idl",
@@ -1156,6 +1161,7 @@ core_idl_files = get_path_info([
                                  "painting/Picture.idl",
                                  "painting/PictureRecorder.idl",
                                  "painting/RRect.idl",
+                                 "painting/Shader.idl",
                                  "view/BeginFrameCallback.idl",
                                  "view/EventCallback.idl",
                                  "view/View.idl",

engine/core/painting/CanvasColor.cpp

@@ -12,16 +12,7 @@
 
 namespace blink {
 
-// Convert dart_color => SkColor.
-SkColor DartConverter<CanvasColor>::FromArgumentsWithNullCheck(
-    Dart_NativeArguments args,
-    int index,
-    Dart_Handle& exception) {
-  SkColor result;
-
-  Dart_Handle dart_color = Dart_GetNativeArgument(args, index);
-  DCHECK(!LogIfError(dart_color));
-
+SkColor DartConverter<CanvasColor>::FromDart(Dart_Handle dart_color) {
   Dart_Handle value =
       Dart_GetField(dart_color, DOMDartState::Current()->value_handle());
 
@@ -30,8 +21,16 @@ SkColor DartConverter<CanvasColor>::FromArgumentsWithNullCheck(
   DCHECK(!LogIfError(rv));
   DCHECK(color <= 0xffffffff);
 
-  result = static_cast<SkColor>(color);
-  return result;
+  return static_cast<SkColor>(color);
+}
+
+SkColor DartConverter<CanvasColor>::FromArgumentsWithNullCheck(
+    Dart_NativeArguments args,
+    int index,
+    Dart_Handle& exception) {
+  Dart_Handle dart_color = Dart_GetNativeArgument(args, index);
+  DCHECK(!LogIfError(dart_color));
+  return FromDart(dart_color);
 }
 
 void DartConverter<CanvasColor>::SetReturnValue(Dart_NativeArguments args,

engine/core/painting/CanvasColor.h

@@ -15,8 +15,15 @@ namespace blink {
 
 class CanvasColor {};
 
+template <>
+struct DartConverterTypes<CanvasColor> {
+  using ConverterType = CanvasColor;
+  using ValueType = SkColor;
+};
+
 template <>
 struct DartConverter<CanvasColor> {
+  static SkColor FromDart(Dart_Handle handle);
   static SkColor FromArgumentsWithNullCheck(Dart_NativeArguments args,
                                             int index,
                                             Dart_Handle& exception);

engine/core/painting/CanvasGradient.cpp

@@ -0,0 +1,40 @@
+// Copyright 2015 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 "sky/engine/config.h"
+#include "sky/engine/core/painting/CanvasGradient.h"
+
+#include "base/logging.h"
+#include "sky/engine/core/painting/Picture.h"
+
+namespace blink {
+
+PassRefPtr<CanvasGradient> CanvasGradient::create(
+    int type,
+    const Vector<Point>& end_points,
+    const Vector<SkColor>& colors,
+    const Vector<float>& color_stops) {
+  ASSERT(type == 0);  // Only 1 supported type so far.
+  ASSERT(end_points.size() == 2);
+  ASSERT(colors.size() == color_stops.size() || color_stops.data() == nullptr);
+  SkPoint sk_end_points[2];
+  for (int i = 0; i < 2; ++i)
+    sk_end_points[i] = end_points[i].sk_point;
+
+  SkShader* shader = SkGradientShader::CreateLinear(
+      sk_end_points, colors.data(), color_stops.data(), colors.size(),
+      SkShader::kClamp_TileMode);
+  return adoptRef(new CanvasGradient(adoptRef(shader)));
+}
+
+CanvasGradient::CanvasGradient(PassRefPtr<SkShader> shader)
+    : Shader(shader)
+{
+}
+
+CanvasGradient::~CanvasGradient()
+{
+}
+
+} // namespace blink

engine/core/painting/CanvasGradient.h

@@ -0,0 +1,31 @@
+// Copyright 2015 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 SKY_ENGINE_CORE_PAINTING_CANVASGRADIENT_H_
+#define SKY_ENGINE_CORE_PAINTING_CANVASGRADIENT_H_
+
+#include "sky/engine/core/painting/CanvasColor.h"
+#include "sky/engine/core/painting/Point.h"
+#include "sky/engine/core/painting/Shader.h"
+#include "sky/engine/tonic/dart_wrappable.h"
+#include "third_party/skia/include/effects/SkGradientShader.h"
+
+namespace blink {
+
+class CanvasGradient : public Shader {
+    DEFINE_WRAPPERTYPEINFO();
+ public:
+  ~CanvasGradient() override;
+  static PassRefPtr<CanvasGradient> create(int type,
+                                           const Vector<Point>& end_points,
+                                           const Vector<SkColor>& colors,
+                                           const Vector<float>& color_stops);
+
+ private:
+  CanvasGradient(PassRefPtr<SkShader> shader);
+};
+
+} // namespace blink
+
+#endif  // SKY_ENGINE_CORE_PAINTING_CANVASGRADIENT_H_

engine/core/painting/Gradient.dart

@@ -0,0 +1,23 @@
+// Copyright 2015 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.
+
+// Extends the generated _Gradient interface via the CustomDart attribute.
+
+class Gradient extends _Gradient {
+  // TODO(mpcomplete): Support other gradient types.
+  // TODO(mpcomplete): Maybe pass a list of (color, colorStop) pairs instead?
+  Gradient.Linear(List<Point> endPoints,
+                  List<Color> colors,
+                  List<double> colorStops)
+      : super(0, endPoints, colors, _validate(colorStops, colors));
+
+  // TODO(mpcomplete): Figure out a good way to validate arguments.
+  static List<double> _validate(colorStops, colors) {
+    if (colorStops != null && colors.length != colorStops.length) {
+      throw new ArgumentError(
+          "[colors] and [colorStops] parameters must be equal length.");
+    }
+    return colorStops;
+  }
+}

engine/core/painting/Gradient.idl

@@ -0,0 +1,10 @@
+// Copyright 2015 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.
+
+[
+    ImplementedAs=CanvasGradient,
+    CustomDart,
+    Constructor(unsigned long gradientType, Point[] endPoints, Color[] colors, float[] colorStops)
+] interface Gradient : Shader {
+};

engine/core/painting/Paint.cpp

@@ -8,6 +8,7 @@
 #include "sky/engine/core/painting/ColorFilter.h"
 #include "sky/engine/core/painting/DrawLooper.h"
 #include "sky/engine/core/painting/MaskFilter.h"
+#include "sky/engine/core/painting/Shader.h"
 
 namespace blink {
 
@@ -37,6 +38,12 @@ void Paint::setMaskFilter(MaskFilter* filter)
     m_paint.setMaskFilter(filter->filter());
 }
 
+void Paint::setShader(Shader* shader)
+{
+    ASSERT(shader);
+    m_paint.setShader(shader->shader());
+}
+
 void Paint::setStyle(SkPaint::Style style)
 {
     m_paint.setStyle(style);

engine/core/painting/Paint.h

@@ -18,6 +18,7 @@ namespace blink {
 class DrawLooper;
 class ColorFilter;
 class MaskFilter;
+class Shader;
 
 class Paint : public RefCounted<Paint>, public DartWrappable {
     DEFINE_WRAPPERTYPEINFO();
@@ -44,6 +45,7 @@ public:
     void setDrawLooper(DrawLooper* looper);
     void setColorFilter(ColorFilter* filter);
     void setMaskFilter(MaskFilter* filter);
+    void setShader(Shader* shader);
     void setStyle(SkPaint::Style style);
     void setTransferMode(SkXfermode::Mode transfer_mode);
 

engine/core/painting/Paint.idl

@@ -14,6 +14,7 @@
   void setDrawLooper(DrawLooper looper);
   void setColorFilter(ColorFilter filter);
   void setMaskFilter(MaskFilter filter);
+  void setShader(Shader shader);
   void setStyle(PaintingStyle style);
   void setTransferMode(TransferMode transferMode);
 };

engine/core/painting/Point.cpp

@@ -11,21 +11,17 @@
 
 namespace blink {
 
-// Convert dartPoint.x,y ==> SkPoint.
-Point DartConverter<Point>::FromArgumentsWithNullCheck(
-    Dart_NativeArguments args,
-    int index,
-    Dart_Handle& exception) {
+// Convert handle.x,y ==> SkPoint.
+Point DartConverter<Point>::FromDart(Dart_Handle handle) {
   Point result;
   result.is_null = true;
 
-  Dart_Handle dartPoint = Dart_GetNativeArgument(args, index);
-  DCHECK(!LogIfError(dartPoint));
+  DCHECK(!LogIfError(handle));
 
   Dart_Handle x_value =
-      Dart_GetField(dartPoint, DOMDartState::Current()->x_handle());
+      Dart_GetField(handle, DOMDartState::Current()->x_handle());
   Dart_Handle y_value =
-      Dart_GetField(dartPoint, DOMDartState::Current()->y_handle());
+      Dart_GetField(handle, DOMDartState::Current()->y_handle());
 
   double x = 0.0, y = 0.0;
   Dart_Handle err = Dart_DoubleValue(x_value, &x);
@@ -37,4 +33,11 @@ Point DartConverter<Point>::FromArgumentsWithNullCheck(
   return result;
 }
 
+Point DartConverter<Point>::FromArgumentsWithNullCheck(
+    Dart_NativeArguments args,
+    int index,
+    Dart_Handle& exception) {
+  return FromDart(Dart_GetNativeArgument(args, index));
+}
+
 } // namespace blink

engine/core/painting/Point.h

@@ -19,6 +19,7 @@ class Point {
 
 template <>
 struct DartConverter<Point> {
+  static Point FromDart(Dart_Handle handle);
   static Point FromArgumentsWithNullCheck(Dart_NativeArguments args,
                                           int index,
                                           Dart_Handle& exception);

engine/core/painting/Shader.cpp

@@ -0,0 +1,17 @@
+// Copyright 2015 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 "sky/engine/config.h"
+#include "sky/engine/core/painting/Shader.h"
+
+namespace blink {
+
+Shader::Shader(PassRefPtr<SkShader> shader)
+    : shader_(shader) {
+}
+
+Shader::~Shader() {
+}
+
+} // namespace blink

engine/core/painting/Shader.h

@@ -0,0 +1,31 @@
+// Copyright 2015 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 SKY_ENGINE_CORE_PAINTING_SHADER_H_
+#define SKY_ENGINE_CORE_PAINTING_SHADER_H_
+
+#include "sky/engine/tonic/dart_wrappable.h"
+#include "sky/engine/wtf/PassRefPtr.h"
+#include "sky/engine/wtf/RefCounted.h"
+#include "third_party/skia/include/core/SkShader.h"
+
+namespace blink {
+
+class Shader : public RefCounted<Shader>, public DartWrappable {
+  DEFINE_WRAPPERTYPEINFO();
+ public:
+  ~Shader() override;
+
+  SkShader* shader() { return shader_.get(); }
+
+ protected:
+  Shader(PassRefPtr<SkShader> shader);
+
+ private:
+  RefPtr<SkShader> shader_;
+};
+
+} // namespace blink
+
+#endif  // SKY_ENGINE_CORE_PAINTING_SHADER_H_

engine/core/painting/Shader.idl

@@ -0,0 +1,6 @@
+// Copyright 2015 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.
+
+interface Shader {
+};

engine/tonic/dart_converter.h

@@ -18,7 +18,24 @@ namespace blink {
 // DartConvert converts types back and forth from Sky to Dart. The template
 // parameter |T| determines what kind of type conversion to perform.
 template <typename T, typename Enable = void>
-struct DartConverter {};
+struct DartConverter {
+};
+
+// This is to work around the fact that typedefs do not create new types. If you
+// have a typedef, and want it to use a different converter, specialize this
+// template and override the types here.
+// Ex:
+//   typedef int ColorType;  // Want to use a different converter.
+//   class ColorConverterType {};  // Dummy type.
+//   template<> struct DartConvertType<ColorConverterType> {
+//     using ConverterType = ColorConverterType;
+//     using ValueType = ColorType;
+//   };
+template <typename T>
+struct DartConverterTypes {
+  using ConverterType = T;
+  using ValueType = T;
+};
 
 ////////////////////////////////////////////////////////////////////////////////
 // Boolean
@@ -227,21 +244,25 @@ struct DartConverter<AtomicString> {
 
 template <typename T>
 struct DartConverter<Vector<T>> {
-  static Dart_Handle ToDart(const Vector<T>& val) {
+  using ValueType = typename DartConverterTypes<T>::ValueType;
+  using ConverterType = typename DartConverterTypes<T>::ConverterType;
+
+  static Dart_Handle ToDart(const Vector<ValueType>& val) {
     Dart_Handle list = Dart_NewList(val.size());
     if (Dart_IsError(list))
       return list;
     for (size_t i = 0; i < val.size(); i++) {
       Dart_Handle result =
-          Dart_ListSetAt(list, i, DartConverter<T>::ToDart(val[i]));
+          Dart_ListSetAt(list, i,
+                         DartConverter<ConverterType>::ToDart(val[i]));
       if (Dart_IsError(result))
         return result;
     }
     return list;
   }
 
-  static Vector<T> FromDart(Dart_Handle handle) {
-    Vector<T> result;
+  static Vector<ValueType> FromDart(Dart_Handle handle) {
+    Vector<ValueType> result;
     if (!Dart_IsList(handle))
       return result;
     intptr_t length = 0;
@@ -251,15 +272,15 @@ struct DartConverter<Vector<T>> {
       Dart_Handle item = Dart_ListGetAt(handle, i);
       DCHECK(!Dart_IsError(item));
       DCHECK(item);
-      result.append(DartConverter<T>::FromDart(item));
+      result.append(DartConverter<ConverterType>::FromDart(item));
     }
     return result;
   }
 
-  static Vector<T> FromArguments(Dart_NativeArguments args,
-                                 int index,
-                                 Dart_Handle& exception,
-                                 bool auto_scope = true) {
+  static Vector<ValueType> FromArguments(Dart_NativeArguments args,
+                                          int index,
+                                          Dart_Handle& exception,
+                                          bool auto_scope = true) {
     // TODO(abarth): What should we do with auto_scope?
     return FromDart(Dart_GetNativeArgument(args, index));
   }

examples/raw/painting.sky

@@ -26,8 +26,12 @@ void main() {
     paint.color = const Color.fromARGB(128, 255, 0, 255);
     context.rotateDegrees(45.0);
 
+    Gradient yellowBlue = new Gradient.Linear(
+        [new Point(-radius, -radius), new Point(0.0, 0.0)],
+        [const Color(0xFFFFFF00), const Color(0xFF0000FF)],
+        null);
     context.drawRect(new Rect.fromLTRB(-radius, -radius, radius, radius),
-                     paint);
+                     new Paint()..setShader(yellowBlue));
 
     // Scale x and y by 0.5.
     var scaleMatrix = new Float32List.fromList([