Fix source blend (flutter#34066)

Author: bdero

impeller/entity/contents/content_context.cc

@@ -41,7 +41,7 @@ void ContentContextOptions::ApplyToPipelineDescriptor(
     case Entity::BlendMode::kSource:
       color0.dst_alpha_blend_factor = BlendFactor::kZero;
       color0.dst_color_blend_factor = BlendFactor::kZero;
-      color0.src_alpha_blend_factor = BlendFactor::kSourceAlpha;
+      color0.src_alpha_blend_factor = BlendFactor::kOne;
       color0.src_color_blend_factor = BlendFactor::kOne;
       break;
     case Entity::BlendMode::kDestination:

impeller/entity/entity_unittests.cc

@@ -10,6 +10,7 @@
 #include "impeller/entity/contents/filters/inputs/filter_input.h"
 #include "impeller/entity/contents/solid_color_contents.h"
 #include "impeller/entity/contents/solid_stroke_contents.h"
+#include "impeller/entity/contents/texture_contents.h"
 #include "impeller/entity/contents/vertices_contents.h"
 #include "impeller/entity/entity.h"
 #include "impeller/entity/entity_pass.h"
@@ -772,38 +773,47 @@ TEST_P(EntityTest, Filters) {
 }
 
 TEST_P(EntityTest, GaussianBlurFilter) {
-  auto bridge = CreateTextureForFixture("bay_bridge.jpg");
   auto boston = CreateTextureForFixture("boston.jpg");
-  auto kalimba = CreateTextureForFixture("kalimba.jpg");
-  ASSERT_TRUE(bridge && boston && kalimba);
+  ASSERT_TRUE(boston);
 
   bool first_frame = true;
   auto callback = [&](ContentContext& context, RenderPass& pass) -> bool {
     if (first_frame) {
       first_frame = false;
-      ImGui::SetNextWindowSize({500, 250});
-      ImGui::SetNextWindowPos({300, 500});
+      ImGui::SetNextWindowSize({500, 290});
+      ImGui::SetNextWindowPos({300, 480});
     }
 
+    const char* input_type_names[] = {"Texture", "Solid Color"};
     const char* blur_type_names[] = {"Image blur", "Mask blur"};
     const char* blur_style_names[] = {"Normal", "Solid", "Outer", "Inner"};
     const FilterContents::BlurStyle blur_styles[] = {
         FilterContents::BlurStyle::kNormal, FilterContents::BlurStyle::kSolid,
         FilterContents::BlurStyle::kOuter, FilterContents::BlurStyle::kInner};
 
     // UI state.
+    static int selected_input_type = 0;
+    static Color input_color = Color::Black();
     static int selected_blur_type = 0;
     static float blur_amount[2] = {20, 20};
     static int selected_blur_style = 0;
     static Color cover_color(1, 0, 0, 0.2);
     static Color bounds_color(0, 1, 0, 0.1);
     static float offset[2] = {500, 400};
     static float rotation = 0;
-    static float scale[2] = {0.5, 0.5};
+    static float scale[2] = {0.75, 0.75};
     static float skew[2] = {0, 0};
 
     ImGui::Begin("Controls");
     {
+      ImGui::Combo("Input type", &selected_input_type, input_type_names,
+                   sizeof(input_type_names) / sizeof(char*));
+      if (selected_input_type == 0) {
+        ImGui::SliderFloat("Input opacity", &input_color.alpha, 0, 1);
+      } else {
+        ImGui::ColorEdit4("Input color",
+                          reinterpret_cast<float*>(&input_color));
+      }
       ImGui::Combo("Blur type", &selected_blur_type, blur_type_names,
                    sizeof(blur_type_names) / sizeof(char*));
       ImGui::SliderFloat2("Blur", &blur_amount[0], 0, 200);
@@ -820,21 +830,39 @@ TEST_P(EntityTest, GaussianBlurFilter) {
     }
     ImGui::End();
 
-    auto blend =
-        FilterContents::MakeBlend(Entity::BlendMode::kScreen,
-                                  FilterInput::Make({boston, bridge, kalimba}));
+    std::shared_ptr<Contents> input;
+    Size input_size;
+
+    if (selected_input_type == 0) {
+      auto texture = std::make_shared<TextureContents>();
+      auto input_rect = Rect::MakeSize(Size(boston->GetSize()));
+      texture->SetSourceRect(input_rect);
+      texture->SetPath(PathBuilder{}.AddRect(input_rect).TakePath());
+      texture->SetTexture(boston);
+      texture->SetOpacity(input_color.alpha);
+
+      input = texture;
+      input_size = input_rect.size;
+    } else {
+      auto fill = std::make_shared<SolidColorContents>();
+      auto input_rect = Rect::MakeSize(Size(boston->GetSize()));
+      fill->SetColor(input_color);
+      fill->SetPath(PathBuilder{}.AddRect(input_rect).TakePath());
+
+      input = fill;
+      input_size = input_rect.size;
+    }
 
     auto blur = FilterContents::MakeGaussianBlur(
-        FilterInput::Make(blend), FilterContents::Sigma{blur_amount[0]},
+        FilterInput::Make(input), FilterContents::Sigma{blur_amount[0]},
         FilterContents::Sigma{blur_amount[1]},
         blur_styles[selected_blur_style]);
 
     auto mask_blur = FilterContents::MakeBorderMaskBlur(
-        FilterInput::Make(bridge), FilterContents::Sigma{blur_amount[0]},
+        FilterInput::Make(input), FilterContents::Sigma{blur_amount[0]},
         FilterContents::Sigma{blur_amount[1]},
         blur_styles[selected_blur_style]);
 
-    auto input_size = bridge->GetSize();
     auto ctm = Matrix::MakeScale(GetContentScale()) *
                Matrix::MakeTranslation(Vector3(offset[0], offset[1])) *
                Matrix::MakeRotationZ(Radians(rotation)) *