Add support for path composition in path builder.

Author: chinmaygarde

impeller/display_list/display_list_impeller.cc

@@ -231,20 +231,22 @@ static PathBuilder::RoundingRadii ToRoundingRadii(const SkRRect& rrect) {
   return radii;
 }
 
+static Path ToPath(const SkPath& path) {
+  UNIMPLEMENTED;
+  return Path{};
+}
+
+static Path ToPath(const SkRRect& rrect) {
+  return PathBuilder{}
+      .AddRoundedRect(ToRect(rrect.getBounds()), ToRoundingRadii(rrect))
+      .TakePath();
+}
+
 // |flutter::Dispatcher|
 void DisplayListImpeller::clipRRect(const SkRRect& rrect,
                                     SkClipOp clip_op,
                                     bool is_aa) {
-  auto path =
-      PathBuilder{}
-          .AddRoundedRect(ToRect(rrect.getBounds()), ToRoundingRadii(rrect))
-          .TakePath();
-  canvas_.ClipPath(std::move(path));
-}
-
-static Path ToPath(const SkPath& path) {
-  UNIMPLEMENTED;
-  return Path{};
+  canvas_.ClipPath(ToPath(rrect));
 }
 
 // |flutter::Dispatcher|
@@ -290,17 +292,16 @@ void DisplayListImpeller::drawCircle(const SkPoint& center, SkScalar radius) {
 
 // |flutter::Dispatcher|
 void DisplayListImpeller::drawRRect(const SkRRect& rrect) {
-  auto path =
-      PathBuilder{}
-          .AddRoundedRect(ToRect(rrect.getBounds()), ToRoundingRadii(rrect))
-          .TakePath();
-  canvas_.DrawPath(std::move(path), paint_);
+  canvas_.DrawPath(ToPath(rrect), paint_);
 }
 
 // |flutter::Dispatcher|
 void DisplayListImpeller::drawDRRect(const SkRRect& outer,
                                      const SkRRect& inner) {
-  UNIMPLEMENTED;
+  PathBuilder builder;
+  builder.AddPath(ToPath(outer));
+  builder.AddPath(ToPath(inner));
+  canvas_.DrawPath(builder.TakePath(FillType::kOdd), paint_);
 }
 
 // |flutter::Dispatcher|

impeller/geometry/path.cc

@@ -155,26 +155,23 @@ bool Path::UpdateCubicComponentAtIndex(size_t index,
   return true;
 }
 
-static void AddPoints(std::vector<Point>& dest, const std::vector<Point>& src) {
-  dest.reserve(dest.size() + src.size());
-  dest.insert(dest.end(), src.begin(), src.end());
-}
-
 std::vector<Point> Path::CreatePolyline(
     const SmoothingApproximation& approximation) const {
   std::vector<Point> points;
+  auto collect_points = [&points](const std::vector<Point>& collection) {
+    points.reserve(points.size() + collection.size());
+    points.insert(points.end(), collection.begin(), collection.end());
+  };
   for (const auto& component : components_) {
     switch (component.type) {
       case ComponentType::kLinear:
-        AddPoints(points, linears_[component.index].CreatePolyline());
+        collect_points(linears_[component.index].CreatePolyline());
         break;
       case ComponentType::kQuadratic:
-        AddPoints(points,
-                  quads_[component.index].CreatePolyline(approximation));
+        collect_points(quads_[component.index].CreatePolyline(approximation));
         break;
       case ComponentType::kCubic:
-        AddPoints(points,
-                  cubics_[component.index].CreatePolyline(approximation));
+        collect_points(cubics_[component.index].CreatePolyline(approximation));
         break;
     }
   }

impeller/geometry/path_builder.cc

@@ -320,4 +320,18 @@ const Path& PathBuilder::GetCurrentPath() const {
   return prototype_;
 }
 
+PathBuilder& PathBuilder::AddPath(const Path& path) {
+  auto linear = [&](size_t index, const LinearPathComponent& l) {
+    prototype_.AddLinearComponent(l.p1, l.p2);
+  };
+  auto quadratic = [&](size_t index, const QuadraticPathComponent& q) {
+    prototype_.AddQuadraticComponent(q.p1, q.cp, q.p2);
+  };
+  auto cubic = [&](size_t index, const CubicPathComponent& c) {
+    prototype_.AddCubicComponent(c.p1, c.cp1, c.cp2, c.p2);
+  };
+  path.EnumerateComponents(linear, quadratic, cubic);
+  return *this;
+}
+
 }  // namespace impeller

impeller/geometry/path_builder.h

@@ -85,6 +85,8 @@ class PathBuilder {
 
   PathBuilder& AddRoundedRect(Rect rect, Scalar radius);
 
+  PathBuilder& AddPath(const Path& path);
+
  private:
   Point subpath_start_;
   Point current_;