Removed linear gradient heap allocation for color conversions between dart and display list (#57108)

issue: flutter/flutter#154650

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Author: gaaclarke

display_list/effects/color_sources/dl_gradient_color_source_base.h

@@ -42,6 +42,10 @@ class DlGradientColorSourceBase : public DlMatrixColorSourceBase {
                          const DlColor* color_data,
                          const float* stop_data);
 
+  void store_color_stops(void* pod,
+                         const DlScalar* color_data_argb,
+                         const float* stop_data);
+
  private:
   DlTileMode mode_;
   uint32_t stop_count_;

display_list/effects/color_sources/dl_linear_gradient_color_source.cc

@@ -20,6 +20,20 @@ DlLinearGradientColorSource::DlLinearGradientColorSource(
   store_color_stops(this + 1, colors, stops);
 }
 
+DlLinearGradientColorSource::DlLinearGradientColorSource(
+    const DlPoint start_point,
+    const DlPoint end_point,
+    uint32_t stop_count,
+    const DlScalar* colors,
+    const float* stops,
+    DlTileMode tile_mode,
+    const DlMatrix* matrix)
+    : DlGradientColorSourceBase(stop_count, tile_mode, matrix),
+      start_point_(start_point),
+      end_point_(end_point) {
+  store_color_stops(this + 1, colors, stops);
+}
+
 DlLinearGradientColorSource::DlLinearGradientColorSource(
     const DlLinearGradientColorSource* source)
     : DlGradientColorSourceBase(source->stop_count(),

display_list/effects/color_sources/dl_linear_gradient_color_source.h

@@ -41,6 +41,14 @@ class DlLinearGradientColorSource final : public DlGradientColorSourceBase {
                               DlTileMode tile_mode,
                               const DlMatrix* matrix = nullptr);
 
+  DlLinearGradientColorSource(const DlPoint start_point,
+                              const DlPoint end_point,
+                              uint32_t stop_count,
+                              const DlScalar* colors,
+                              const float* stops,
+                              DlTileMode tile_mode,
+                              const DlMatrix* matrix = nullptr);
+
   explicit DlLinearGradientColorSource(
       const DlLinearGradientColorSource* source);
 

display_list/effects/dl_color_source.cc

@@ -30,6 +30,13 @@ std::shared_ptr<DlColorSource> DlColorSource::MakeImage(
       image, horizontal_tile_mode, vertical_tile_mode, sampling, matrix);
 }
 
+namespace {
+size_t CalculateLinearGradientSize(uint32_t stop_count) {
+  return sizeof(DlLinearGradientColorSource) +
+         (stop_count * (sizeof(DlColor) + sizeof(float)));
+}
+}  // namespace
+
 std::shared_ptr<DlColorSource> DlColorSource::MakeLinear(
     const DlPoint start_point,
     const DlPoint end_point,
@@ -38,9 +45,7 @@ std::shared_ptr<DlColorSource> DlColorSource::MakeLinear(
     const float* stops,
     DlTileMode tile_mode,
     const DlMatrix* matrix) {
-  size_t needed = sizeof(DlLinearGradientColorSource) +
-                  (stop_count * (sizeof(DlColor) + sizeof(float)));
-
+  size_t needed = CalculateLinearGradientSize(stop_count);
   void* storage = ::operator new(needed);
 
   std::shared_ptr<DlLinearGradientColorSource> ret;
@@ -51,6 +56,25 @@ std::shared_ptr<DlColorSource> DlColorSource::MakeLinear(
   return ret;
 }
 
+std::shared_ptr<DlColorSource> DlColorSource::MakeLinear(
+    const DlPoint start_point,
+    const DlPoint end_point,
+    uint32_t stop_count,
+    const DlScalar* colors_argb,
+    const float* stops,
+    DlTileMode tile_mode,
+    const DlMatrix* matrix) {
+  size_t needed = CalculateLinearGradientSize(stop_count);
+  void* storage = ::operator new(needed);
+
+  std::shared_ptr<DlLinearGradientColorSource> ret;
+  ret.reset(new (storage) DlLinearGradientColorSource(start_point, end_point,
+                                                      stop_count, colors_argb,
+                                                      stops, tile_mode, matrix),
+            DlGradientDeleter);
+  return ret;
+}
+
 std::shared_ptr<DlColorSource> DlColorSource::MakeRadial(
     DlPoint center,
     DlScalar radius,
@@ -157,23 +181,72 @@ bool DlGradientColorSourceBase::base_equals_(
                  stop_count_ * sizeof(stops()[0])) == 0);
 }
 
-void DlGradientColorSourceBase::store_color_stops(void* pod,
-                                                  const DlColor* color_data,
-                                                  const float* stop_data) {
+namespace {
+template <typename DlColorIt>
+void do_store_color_stops(void* pod,
+                          DlColorIt color_data_argb_begin,
+                          DlColorIt color_data_argb_end,
+                          const float* stop_data) {
   DlColor* color_storage = reinterpret_cast<DlColor*>(pod);
-  memcpy(color_storage, color_data, stop_count_ * sizeof(*color_data));
-  float* stop_storage = reinterpret_cast<float*>(color_storage + stop_count_);
+  uint32_t stop_count = 0;
+  while (color_data_argb_begin < color_data_argb_end) {
+    *color_storage++ = *color_data_argb_begin++;
+    stop_count += 1;
+  }
+  float* stop_storage = reinterpret_cast<float*>(color_storage);
   if (stop_data) {
-    memcpy(stop_storage, stop_data, stop_count_ * sizeof(*stop_data));
+    memcpy(stop_storage, stop_data, stop_count * sizeof(*stop_data));
   } else {
-    float div = stop_count_ - 1;
+    float div = stop_count - 1;
     if (div <= 0) {
       div = 1;
     }
-    for (uint32_t i = 0; i < stop_count_; i++) {
+    for (uint32_t i = 0; i < stop_count; i++) {
       stop_storage[i] = i / div;
     }
   }
 }
 
+class DlScalerToDlColorIterator {
+ public:
+  explicit DlScalerToDlColorIterator(const DlScalar* ptr) : ptr_(ptr) {}
+  DlScalerToDlColorIterator(DlScalerToDlColorIterator&&) = default;
+  DlScalerToDlColorIterator(const DlScalerToDlColorIterator&) = delete;
+  DlScalerToDlColorIterator& operator=(const DlScalerToDlColorIterator&) =
+      delete;
+
+  DlColor operator*() {
+    return DlColor(ptr_[0], ptr_[1], ptr_[2], ptr_[3],
+                   DlColorSpace::kExtendedSRGB);
+  }
+  DlScalerToDlColorIterator operator++(int) {
+    auto result = DlScalerToDlColorIterator(ptr_);
+    ptr_ += 4;
+    return result;
+  }
+  bool operator<(const DlScalerToDlColorIterator& that) const {
+    return ptr_ < that.ptr_;
+  }
+
+ private:
+  const DlScalar* ptr_;
+};
+
+}  // namespace
+
+void DlGradientColorSourceBase::store_color_stops(void* pod,
+                                                  const DlColor* color_data,
+                                                  const float* stop_data) {
+  do_store_color_stops(pod, color_data, color_data + stop_count_, stop_data);
+}
+
+void DlGradientColorSourceBase::store_color_stops(
+    void* pod,
+    const DlScalar* color_data_argb,
+    const float* stop_data) {
+  do_store_color_stops(
+      pod, DlScalerToDlColorIterator(color_data_argb),
+      DlScalerToDlColorIterator(color_data_argb + stop_count_ * 4), stop_data);
+}
+
 }  // namespace flutter

display_list/effects/dl_color_source.h

@@ -59,6 +59,17 @@ class DlColorSource : public DlAttribute<DlColorSource, DlColorSourceType> {
       DlTileMode tile_mode,
       const DlMatrix* matrix = nullptr);
 
+  /// @brief Make a linear gradient.
+  /// @param colors_argb Array of DlScalars that represents colors in the ARGB.
+  static std::shared_ptr<DlColorSource> MakeLinear(
+      const DlPoint start_point,
+      const DlPoint end_point,
+      uint32_t stop_count,
+      const DlScalar* colors_argb,
+      const float* stops,
+      DlTileMode tile_mode,
+      const DlMatrix* matrix = nullptr);
+
   static std::shared_ptr<DlColorSource> MakeRadial(
       DlPoint center,
       DlScalar radius,

display_list/effects/dl_color_source_unittests.cc

@@ -189,6 +189,32 @@ TEST(DisplayListColorSource, LinearGradientConstructor) {
       DlTileMode::kClamp, &kTestMatrix1);
 }
 
+TEST(DisplayListColorSource, LinearGradientARGBConstructor) {
+  std::array<DlScalar, kTestStopCount * 4> colors;
+  for (int i = 0; i < kTestStopCount; ++i) {
+    colors[i * 4 + 0] = kTestColors[i].getAlphaF();  //
+    colors[i * 4 + 1] = kTestColors[i].getRedF();    //
+    colors[i * 4 + 2] = kTestColors[i].getGreenF();  //
+    colors[i * 4 + 3] = kTestColors[i].getBlueF();
+  }
+  std::shared_ptr<DlColorSource> source = DlColorSource::MakeLinear(
+      kTestPoints[0], kTestPoints[1], kTestStopCount, colors.data(), kTestStops,
+      DlTileMode::kClamp, &kTestMatrix1);
+  ASSERT_TRUE(source);
+  ASSERT_TRUE(source->asLinearGradient());
+  EXPECT_EQ(source->asLinearGradient()->start_point(), kTestPoints[0]);
+  EXPECT_EQ(source->asLinearGradient()->end_point(), kTestPoints[1]);
+  EXPECT_EQ(source->asLinearGradient()->stop_count(), kTestStopCount);
+  for (int i = 0; i < kTestStopCount; i++) {
+    EXPECT_EQ(source->asLinearGradient()->colors()[i],
+              kTestColors[i].withColorSpace(DlColorSpace::kExtendedSRGB));
+    EXPECT_EQ(source->asLinearGradient()->stops()[i], kTestStops[i]);
+  }
+  EXPECT_EQ(source->asLinearGradient()->tile_mode(), DlTileMode::kClamp);
+  EXPECT_EQ(source->asLinearGradient()->matrix(), kTestMatrix1);
+  EXPECT_EQ(source->is_opaque(), true);
+}
+
 TEST(DisplayListColorSource, LinearGradientShared) {
   std::shared_ptr<DlColorSource> source = DlColorSource::MakeLinear(
       kTestPoints[0], kTestPoints[1], kTestStopCount, kTestColors, kTestStops,

display_list/skia/dl_sk_conversions_unittests.cc

@@ -302,7 +302,8 @@ TEST(DisplayListSkConversions, ToSkDitheringEnabledForGradients) {
 
   // Set the paint to be a gradient.
   dl_paint.setColorSource(DlColorSource::MakeLinear(
-      DlPoint(0, 0), DlPoint(100, 100), 0, 0, 0, DlTileMode::kClamp));
+      DlPoint(0, 0), DlPoint(100, 100), 0,
+      std::array<DlColor, 1>{DlColor(0)}.data(), 0, DlTileMode::kClamp));
 
   {
     SkPaint sk_paint = ToSk(dl_paint);

lib/ui/painting/gradient.cc

@@ -44,17 +44,7 @@ void CanvasGradient::initLinear(const tonic::Float32List& end_points,
 
   DlPoint p0 = DlPoint(end_points[0], end_points[1]);
   DlPoint p1 = DlPoint(end_points[2], end_points[3]);
-  std::vector<DlColor> dl_colors;
-  dl_colors.reserve(num_colors);
-  for (int i = 0; i < colors.num_elements(); i += 4) {
-    DlScalar a = colors[i + 0];
-    DlScalar r = colors[i + 1];
-    DlScalar g = colors[i + 2];
-    DlScalar b = colors[i + 3];
-    dl_colors.emplace_back(DlColor(a, r, g, b, DlColorSpace::kExtendedSRGB));
-  }
-
-  dl_shader_ = DlColorSource::MakeLinear(p0, p1, num_colors, dl_colors.data(),
+  dl_shader_ = DlColorSource::MakeLinear(p0, p1, num_colors, colors.data(),
                                          color_stops.data(), tile_mode,
                                          has_matrix ? &dl_matrix : nullptr);
   // Just a sanity check, all gradient shaders should be thread-safe