Started filtering out close line segments in rrect polylines. (flutter/engine#55929)

fixes https://github.com/flutter/flutter/issues/156422

tests: AiksTest.GradientOvalStrokeMaskBlurSigmaZero

This filtering needs to happen somewheres.  I opted for putting it inside of the AddLinearComponent instead of where it was affected me in the test: 45237cc63f/impeller/geometry/path_builder.cc (L180)

This seems preferable.  A tiny line segment should never matter.  The rub is that its only happening here.  We might want to do this in other places as well.  It's equally unimportant to have a tiny curve.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

engine/src/flutter/impeller/display_list/aiks_dl_basic_unittests.cc

@@ -1534,5 +1534,50 @@ TEST_P(AiksTest, MassiveScalingMatrixImageFilter) {
   ASSERT_TRUE(OpenPlaygroundHere(builder.Build()));
 }
 
+TEST_P(AiksTest, NoDimplesInRRectPath) {
+  Scalar width = 200.f;
+  Scalar height = 60.f;
+  Scalar corner = 1.f;
+  auto callback = [&]() -> sk_sp<DisplayList> {
+    if (AiksTest::ImGuiBegin("Controls", nullptr,
+                             ImGuiWindowFlags_AlwaysAutoResize)) {
+      ImGui::SliderFloat("width", &width, 0, 200);
+      ImGui::SliderFloat("height", &height, 0, 200);
+      ImGui::SliderFloat("corner", &corner, 0, 1);
+      ImGui::End();
+    }
+
+    DisplayListBuilder builder;
+    builder.Scale(GetContentScale().x, GetContentScale().y);
+
+    DlPaint background_paint;
+    background_paint.setColor(DlColor(1, 0.1, 0.1, 0.1, DlColorSpace::kSRGB));
+    builder.DrawPaint(background_paint);
+
+    std::vector<DlColor> colors = {DlColor::kRed(), DlColor::kBlue()};
+    std::vector<Scalar> stops = {0.0, 1.0};
+
+    DlPaint paint;
+    auto gradient = DlColorSource::MakeLinear(
+        {0, 0}, {200, 200}, 2, colors.data(), stops.data(), DlTileMode::kClamp);
+    paint.setColorSource(gradient);
+    paint.setColor(DlColor::kWhite());
+    paint.setDrawStyle(DlDrawStyle::kStroke);
+    paint.setStrokeWidth(20);
+
+    builder.Save();
+    builder.Translate(100, 100);
+
+    Scalar corner_x = ((1 - corner) * 50) + 50;
+    Scalar corner_y = corner * 50 + 50;
+    SkRRect rrect = SkRRect::MakeRectXY(SkRect::MakeXYWH(0, 0, width, height),
+                                        corner_x, corner_y);
+    builder.DrawRRect(rrect, paint);
+    builder.Restore();
+    return builder.Build();
+  };
+  ASSERT_TRUE(OpenPlaygroundHere(callback));
+}
+
 }  // namespace testing
 }  // namespace impeller

engine/src/flutter/impeller/geometry/path_builder.cc

@@ -165,7 +165,7 @@ PathBuilder& PathBuilder::AddRoundedRect(Rect rect, RoundingRadii radii) {
   //----------------------------------------------------------------------------
   // Top line.
   //
-  AddLinearComponent(
+  AddLinearComponentIfNeeded(
       {rect_origin.x + radii.top_left.x, rect_origin.y},
       {rect_origin.x + rect_size.width - radii.top_right.x, rect_origin.y});
 
@@ -177,7 +177,7 @@ PathBuilder& PathBuilder::AddRoundedRect(Rect rect, RoundingRadii radii) {
   //----------------------------------------------------------------------------
   // Right line.
   //
-  AddLinearComponent(
+  AddLinearComponentIfNeeded(
       {rect_origin.x + rect_size.width, rect_origin.y + radii.top_right.y},
       {rect_origin.x + rect_size.width,
        rect_origin.y + rect_size.height - radii.bottom_right.y});
@@ -190,7 +190,7 @@ PathBuilder& PathBuilder::AddRoundedRect(Rect rect, RoundingRadii radii) {
   //----------------------------------------------------------------------------
   // Bottom line.
   //
-  AddLinearComponent(
+  AddLinearComponentIfNeeded(
       {rect_origin.x + rect_size.width - radii.bottom_right.x,
        rect_origin.y + rect_size.height},
       {rect_origin.x + radii.bottom_left.x, rect_origin.y + rect_size.height});
@@ -203,7 +203,7 @@ PathBuilder& PathBuilder::AddRoundedRect(Rect rect, RoundingRadii radii) {
   //----------------------------------------------------------------------------
   // Left line.
   //
-  AddLinearComponent(
+  AddLinearComponentIfNeeded(
       {rect_origin.x, rect_origin.y + rect_size.height - radii.bottom_left.y},
       {rect_origin.x, rect_origin.y + radii.top_left.y});
 
@@ -283,6 +283,14 @@ void PathBuilder::AddContourComponent(const Point& destination,
   prototype_.bounds.reset();
 }
 
+void PathBuilder::AddLinearComponentIfNeeded(const Point& p1, const Point& p2) {
+  if (ScalarNearlyEqual(p1.x, p2.x, 1e-4f) &&
+      ScalarNearlyEqual(p1.y, p2.y, 1e-4f)) {
+    return;
+  }
+  AddLinearComponent(p1, p2);
+}
+
 void PathBuilder::AddLinearComponent(const Point& p1, const Point& p2) {
   auto& points = prototype_.points;
   points.push_back(p1);

engine/src/flutter/impeller/geometry/path_builder.h

@@ -173,6 +173,8 @@ class PathBuilder {
 
   void AddLinearComponent(const Point& p1, const Point& p2);
 
+  void AddLinearComponentIfNeeded(const Point& p1, const Point& p2);
+
   void AddQuadraticComponent(const Point& p1, const Point& cp, const Point& p2);
 
   void AddCubicComponent(const Point& p1,

engine/src/flutter/testing/impeller_golden_tests_output.txt

@@ -819,6 +819,9 @@ impeller_Play_AiksTest_MatrixSaveLayerFilter_Vulkan.png
 impeller_Play_AiksTest_MipmapGenerationWorksCorrectly_Metal.png
 impeller_Play_AiksTest_MipmapGenerationWorksCorrectly_OpenGLES.png
 impeller_Play_AiksTest_MipmapGenerationWorksCorrectly_Vulkan.png
+impeller_Play_AiksTest_NoDimplesInRRectPath_Metal.png
+impeller_Play_AiksTest_NoDimplesInRRectPath_OpenGLES.png
+impeller_Play_AiksTest_NoDimplesInRRectPath_Vulkan.png
 impeller_Play_AiksTest_PaintBlendModeIsRespected_Metal.png
 impeller_Play_AiksTest_PaintBlendModeIsRespected_OpenGLES.png
 impeller_Play_AiksTest_PaintBlendModeIsRespected_Vulkan.png