From 0b707db40bb6b545d2a4c57be46f060fcac3a904 Mon Sep 17 00:00:00 2001
From: Brandon DeRosier <bdero@google.com>
Date: Fri, 25 Feb 2022 13:24:14 -0800
Subject: [PATCH] Remove duplicate points between connected components when
 generating polylines (flutter/engine#34)

---
 .../impeller/geometry/geometry_unittests.cc   | 19 +++++++++++++++++++
 engine/src/flutter/impeller/geometry/path.cc  | 16 +++++++++++++---
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/engine/src/flutter/impeller/geometry/geometry_unittests.cc b/engine/src/flutter/impeller/geometry/geometry_unittests.cc
index 4c0f2e33404..2d551d32ee9 100644
--- a/engine/src/flutter/impeller/geometry/geometry_unittests.cc
+++ b/engine/src/flutter/impeller/geometry/geometry_unittests.cc
@@ -636,5 +636,24 @@ TEST(GeometryTest, CubicPathComponentPolylineDoesNotIncludePointOne) {
   ASSERT_EQ(polyline.back().y, 40);
 }
 
+TEST(GeometryTest, PathCreatePolyLineDoesNotDuplicatePoints) {
+  Path path;
+  path.AddMoveComponent({10, 10});
+  path.AddLinearComponent({10, 10}, {20, 20});
+  path.AddLinearComponent({20, 20}, {30, 30});
+  path.AddMoveComponent({40, 40});
+  path.AddLinearComponent({40, 40}, {50, 50});
+
+  auto polyline = path.CreatePolyline();
+
+  ASSERT_EQ(polyline.breaks.size(), 2u);
+  ASSERT_EQ(polyline.points.size(), 5u);
+  ASSERT_EQ(polyline.points[0].x, 10);
+  ASSERT_EQ(polyline.points[1].x, 20);
+  ASSERT_EQ(polyline.points[2].x, 30);
+  ASSERT_EQ(polyline.points[3].x, 40);
+  ASSERT_EQ(polyline.points[4].x, 50);
+}
+
 }  // namespace testing
 }  // namespace impeller
diff --git a/engine/src/flutter/impeller/geometry/path.cc b/engine/src/flutter/impeller/geometry/path.cc
index a5c0268bfc1..4bacb04ea9b 100644
--- a/engine/src/flutter/impeller/geometry/path.cc
+++ b/engine/src/flutter/impeller/geometry/path.cc
@@ -197,9 +197,18 @@ bool Path::UpdateMoveComponentAtIndex(size_t index,
 Path::Polyline Path::CreatePolyline(
     const SmoothingApproximation& approximation) const {
   Polyline polyline;
-  auto collect_points = [&polyline](const std::vector<Point>& collection) {
-    polyline.points.reserve(polyline.points.size() + collection.size());
-    polyline.points.insert(polyline.points.end(), collection.begin(),
+  // TODO(99177): Refactor this to have component polyline creation always
+  //              exclude the first point, and append the destination point for
+  //              move components. See issue for details.
+  bool new_contour = true;
+  auto collect_points = [&polyline,
+                         &new_contour](const std::vector<Point>& collection) {
+    size_t offset = new_contour ? 0 : 1;
+    new_contour = false;
+
+    polyline.points.reserve(polyline.points.size() + collection.size() -
+                            offset);
+    polyline.points.insert(polyline.points.end(), collection.begin() + offset,
                            collection.end());
   };
   for (const auto& component : components_) {
@@ -215,6 +224,7 @@ Path::Polyline Path::CreatePolyline(
         break;
       case ComponentType::kMove:
         polyline.breaks.insert(polyline.points.size());
+        new_contour = true;
         break;
     }
   }