Don't add duplicate points when clipping

cc/base/math_util_unittest.cc

 // Copyright 2012 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/base/math_util.h"
 
 #include <stdint.h>
 
 #include <cmath>
 
 #include "cc/test/geometry_test_utils.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
+#include "ui/gfx/geometry/quad_f.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/rect_f.h"
 #include "ui/gfx/transform.h"
 
 namespace cc {
 namespace {
 
 TEST(MathUtilTest, ProjectionOfPerpendicularPlane) {
   // In this case, the m33() element of the transform becomes zero, which could
   // cause a divide-by-zero when projecting points/quads.
@@ skipping 424 matching lines @@
   }
 }
 
 TEST(MathUtilTest, RoundDownUnderflow) {
   // Rounding down -123 by 50 is -150, which underflows int8_t, but fits in
   // int16_t.
   EXPECT_FALSE(MathUtil::VerifyRoundDown<int8_t>(-123, 50));
   EXPECT_TRUE(MathUtil::VerifyRoundDown<int16_t>(-123, 50));
 }
 
+TEST(MathUtilTest, MapClippedQuadDuplicate) {
+  gfx::Transform transform;
+  transform.MakeIdentity();
+  transform.ApplyPerspectiveDepth(50.0);
+  transform.RotateAboutYAxis(89.0);
+
+  gfx::QuadF src_quad(gfx::PointF(0.0f, 100.0f), gfx::PointF(0.0f, -100.0f),

[flackr, 2016/12/08 20:24:01]

It might be worth explicitly pointing out the two vertices which clip to the
same point in a comment. It's the last two right?

[Peter Mayo, 2016/12/08 20:29:09]

Actually a comment about the whole scenario may be even better.

+                      gfx::PointF(-99.0f, -300.0f),
+                      gfx::PointF(-99.0f, -100.0f));
+
+  gfx::PointF clipped_quad[8];
+  int num_vertices_in_clipped_quad;
+
+  MathUtil::MapClippedQuad(transform, src_quad, clipped_quad,
+                           &num_vertices_in_clipped_quad);
+
+  printf("transformed quad is [");
+  for (int i = 0; i < num_vertices_in_clipped_quad; i++) {
+    if (i > 0)
+      printf(", ");
+    printf("(%.5f, %.5f)", clipped_quad[i].x(), clipped_quad[i].y());
+  }
+  printf("]\n");

[flackr, 2016/12/08 20:24:01]

debugging code?

[Peter Mayo, 2016/12/08 20:29:09]

Yup, hence 'First ...

Definitely more to come, and needed to discuss the other point.

+
+  EXPECT_EQ(num_vertices_in_clipped_quad, 3);
+}
+
 }  // namespace
 }  // namespace cc