Correct polygon splitting in an almost-coplanar case.

cc/quads/draw_polygon.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/quads/draw_polygon.h"
 
 #include <stddef.h>
 
 #include <vector>
 
@@ skipping 270 matching lines @@
       polygon->points_[pre_back_begin], polygon->points_[back_begin],
       -vertex_distance[pre_back_begin] /
           gfx::DotProduct(normal_, polygon->points_[back_begin] -
                                        polygon->points_[pre_back_begin]),
       &pre_neg_intersection);
 
   // Build the front and back polygons.
   std::vector<gfx::Point3F> out_points;
 
   out_points.push_back(pre_pos_intersection);
-  do {
-    out_points.push_back(polygon->points_[front_begin]);
-    front_begin = next(front_begin);
-  } while (vertex_distance[front_begin] > 0.0);
-  out_points.push_back(pre_neg_intersection);
+  for (size_t index = front_begin; index != back_begin; index = next(index)) {
+    out_points.push_back(polygon->points_[index]);
+  }
+  if (out_points.back() != pre_neg_intersection) {
+    out_points.push_back(pre_neg_intersection);
+  }
   *front =
       base::MakeUnique<DrawPolygon>(polygon->original_ref_, out_points,
                                     polygon->normal_, polygon->order_index_);
 
   out_points.clear();
 
   out_points.push_back(pre_neg_intersection);
-  do {
-    out_points.push_back(polygon->points_[back_begin]);
-    back_begin = next(back_begin);
-  } while (vertex_distance[back_begin] < 0.0);
-  out_points.push_back(pre_pos_intersection);
+  for (size_t index = back_begin; index != front_begin; index = next(index)) {
+    out_points.push_back(polygon->points_[index]);
+  }
+  if (out_points.back() != pre_pos_intersection) {
+    out_points.push_back(pre_pos_intersection);
+  }
   *back =
       base::MakeUnique<DrawPolygon>(polygon->original_ref_, out_points,
                                     polygon->normal_, polygon->order_index_);
 
   DCHECK_GE((*front)->points().size(), 3u);
   DCHECK_GE((*back)->points().size(), 3u);
 }
 
 // This algorithm takes the first vertex in the polygon and uses that as a
 // pivot point to fan out and create quads from the rest of the vertices.
@@ skipping 22 matching lines @@
     quads->push_back(
         gfx::QuadF(first,
                    gfx::PointF(points_[offset].x(), points_[offset].y()),
                    gfx::PointF(points_[op1].x(), points_[op1].y()),
                    gfx::PointF(points_[op2].x(), points_[op2].y())));
     offset = op2;
   }
 }
 
 }  // namespace cc