WIP BSP Tree for 3D Layer Sorting

Still adding test scenarios as I come up with them.

Review URL: https://codereview.chromium.org/384083002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286499 0039d316-1c4b-4281-b951-d872f2087c98

7 files changed, 646 insertions, 1 deletions

diff --git a/cc/cc.gyp b/cc/cc.gyp
index 67a50326..83d408e 100644
--- a/cc/cc.gyp
+++ b/cc/cc.gyp
@@ -244,7 +244,10 @@
         'layers/video_layer_impl.h',
         'output/begin_frame_args.cc',
         'output/begin_frame_args.h',
-        'output/bsp_compare_result.h',
+        'output/bsp_tree.cc',
+        'output/bsp_tree.h',
+        'output/bsp_walk_action.cc',
+        'output/bsp_walk_action.h',
         'output/compositor_frame.cc',
         'output/compositor_frame.h',
         'output/compositor_frame_ack.cc',
diff --git a/cc/cc_tests.gyp b/cc/cc_tests.gyp
index d29413d..18d38f9 100644
--- a/cc/cc_tests.gyp
+++ b/cc/cc_tests.gyp
@@ -58,6 +58,7 @@
       'layers/ui_resource_layer_unittest.cc',
       'layers/video_layer_impl_unittest.cc',
       'output/begin_frame_args_unittest.cc',
+      'output/bsp_tree_unittest.cc',
       'output/delegating_renderer_unittest.cc',
       'output/filter_operations_unittest.cc',
       'output/gl_renderer_unittest.cc',
diff --git a/cc/output/bsp_tree.cc b/cc/output/bsp_tree.cc
new file mode 100644
index 0000000..2755c0b
--- /dev/null
+++ b/cc/output/bsp_tree.cc
@@ -0,0 +1,121 @@
+// 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/output/bsp_tree.h"
+
+#include <list>
+#include <vector>
+
+#include "base/memory/scoped_ptr.h"
+#include "cc/base/scoped_ptr_deque.h"
+#include "cc/base/scoped_ptr_vector.h"
+#include "cc/output/bsp_compare_result.h"
+#include "cc/quads/draw_polygon.h"
+
+namespace cc {
+
+BspNode::BspNode(scoped_ptr<DrawPolygon> data) : node_data(data.Pass()) {
+}
+
+BspNode::~BspNode() {
+}
+
+BspTree::BspTree(ScopedPtrDeque<DrawPolygon>* list) {
+  if (list->size() == 0)
+    return;
+
+  root_ = scoped_ptr<BspNode>(new BspNode(list->take_front()));
+  BuildTree(root_.get(), list);
+}
+
+// The idea behind using a deque for BuildTree's input is that we want to be
+// able to place polygons that we've decided aren't splitting plane candidates
+// at the back of the queue while moving the candidate splitting planes to the
+// front when the heuristic decides that they're a better choice. This way we
+// can always simply just take from the front of the deque for our node's
+// data.
+void BspTree::BuildTree(BspNode* node,
+                        ScopedPtrDeque<DrawPolygon>* polygon_list) {
+  ScopedPtrDeque<DrawPolygon> front_list;
+  ScopedPtrDeque<DrawPolygon> back_list;
+
+  // We take in a list of polygons at this level of the tree, and have to
+  // find a splitting plane, then classify polygons as either in front of
+  // or behind that splitting plane.
+  while (polygon_list->size() > 0) {
+    // Is this particular polygon in front of or behind our splitting polygon.
+    BspCompareResult comparer_result =
+        GetNodePositionRelative(*polygon_list->front(), *(node->node_data));
+
+    // If it's clearly behind or in front of the splitting plane, we use the
+    // heuristic to decide whether or not we should put it at the back
+    // or front of the list.
+    switch (comparer_result) {
+      case BSP_FRONT:
+        front_list.push_back(polygon_list->take_front().Pass());
+        break;
+      case BSP_BACK:
+        back_list.push_back(polygon_list->take_front().Pass());
+        break;
+      case BSP_SPLIT:
+      {
+        scoped_ptr<DrawPolygon> polygon;
+        scoped_ptr<DrawPolygon> new_front;
+        scoped_ptr<DrawPolygon> new_back;
+        bool split_result = false;
+        // Time to split this geometry, *it needs to be split by node_data.
+        polygon = polygon_list->take_front();
+        split_result =
+            polygon->Split(*(node->node_data), &new_front, &new_back);
+        DCHECK(split_result);
+        if (!split_result) {
+          break;
+        }
+        front_list.push_back(new_front.Pass());
+        back_list.push_back(new_back.Pass());
+        break;
+      }
+      case BSP_COPLANAR_FRONT:
+        node->coplanars_front.push_back(polygon_list->take_front());
+        break;
+      case BSP_COPLANAR_BACK:
+        node->coplanars_back.push_back(polygon_list->take_front());
+        break;
+      default:
+        NOTREACHED();
+        break;
+    }
+  }
+
+  // Build the back subtree using the front of the back_list as our splitter.
+  if (back_list.size() > 0) {
+    node->back_child = scoped_ptr<BspNode>(new BspNode(back_list.take_front()));
+    BuildTree(node->back_child.get(), &back_list);
+  }
+
+  // Build the front subtree using the front of the front_list as our splitter.
+  if (front_list.size() > 0) {
+    node->front_child =
+        scoped_ptr<BspNode>(new BspNode(front_list.take_front()));
+    BuildTree(node->front_child.get(), &front_list);
+  }
+}
+
+BspCompareResult BspTree::GetNodePositionRelative(const DrawPolygon& node_a,
+                                                  const DrawPolygon& node_b) {
+  return DrawPolygon::SideCompare(node_a, node_b);
+}
+
+// The base comparer with 0,0,0 as camera position facing forward
+BspCompareResult BspTree::GetCameraPositionRelative(const DrawPolygon& node) {
+  if (node.normal().z() > 0.0f) {
+    return BSP_FRONT;
+  }
+  return BSP_BACK;
+}
+
+BspTree::~BspTree() {
+}
+
+}  // namespace cc
diff --git a/cc/output/bsp_tree.h b/cc/output/bsp_tree.h
new file mode 100644
index 0000000..6e7f66b
--- /dev/null
+++ b/cc/output/bsp_tree.h
@@ -0,0 +1,115 @@
+// 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.
+
+#ifndef CC_OUTPUT_BSP_TREE_H_
+#define CC_OUTPUT_BSP_TREE_H_
+
+#include <list>
+#include <vector>
+
+#include "base/memory/scoped_ptr.h"
+#include "cc/base/scoped_ptr_deque.h"
+#include "cc/base/scoped_ptr_vector.h"
+#include "cc/output/bsp_compare_result.h"
+#include "cc/quads/draw_polygon.h"
+
+namespace cc {
+
+struct BspNode {
+  // This represents the splitting plane.
+  scoped_ptr<DrawPolygon> node_data;
+  // This represents any coplanar geometry we found while building the BSP.
+  ScopedPtrVector<DrawPolygon> coplanars_front;
+  ScopedPtrVector<DrawPolygon> coplanars_back;
+
+  scoped_ptr<BspNode> back_child;
+  scoped_ptr<BspNode> front_child;
+
+  explicit BspNode(scoped_ptr<DrawPolygon> data);
+  ~BspNode();
+};
+
+class CC_EXPORT BspTree {
+ public:
+  explicit BspTree(ScopedPtrDeque<DrawPolygon>* list);
+  scoped_ptr<BspNode>& root() { return root_; }
+
+  template <typename ActionHandlerType>
+  void TraverseWithActionHandler(ActionHandlerType* action_handler) const {
+    if (root_) {
+      WalkInOrderRecursion<ActionHandlerType>(action_handler, root_.get());
+    }
+  }
+
+  ~BspTree();
+
+ private:
+  scoped_ptr<BspNode> root_;
+
+  void FromList(ScopedPtrVector<DrawPolygon>* list);
+  void BuildTree(BspNode* node, ScopedPtrDeque<DrawPolygon>* data);
+
+  template <typename ActionHandlerType>
+  void WalkInOrderAction(ActionHandlerType* action_handler,
+                         DrawPolygon* item) const {
+    (*action_handler)(item);
+  }
+
+  template <typename ActionHandlerType>
+  void WalkInOrderVisitNodes(
+      ActionHandlerType* action_handler,
+      const BspNode* node,
+      const BspNode* first_child,
+      const BspNode* second_child,
+      const ScopedPtrVector<DrawPolygon>& first_coplanars,
+      const ScopedPtrVector<DrawPolygon>& second_coplanars) const {
+    if (first_child) {
+      WalkInOrderRecursion(action_handler, first_child);
+    }
+    for (size_t i = 0; i < first_coplanars.size(); i++) {
+      WalkInOrderAction(action_handler, first_coplanars[i]);
+    }
+    WalkInOrderAction(action_handler, node->node_data.get());
+    for (size_t i = 0; i < second_coplanars.size(); i++) {
+      WalkInOrderAction(action_handler, second_coplanars[i]);
+    }
+    if (second_child) {
+      WalkInOrderRecursion(action_handler, second_child);
+    }
+  }
+
+  template <typename ActionHandlerType>
+  void WalkInOrderRecursion(ActionHandlerType* action_handler,
+                            const BspNode* node) const {
+    // If our view is in front of the the polygon
+    // in this node then walk back then front.
+    if (GetCameraPositionRelative(*(node->node_data)) == BSP_FRONT) {
+      WalkInOrderVisitNodes<ActionHandlerType>(action_handler,
+                                               node,
+                                               node->back_child.get(),
+                                               node->front_child.get(),
+                                               node->coplanars_front,
+                                               node->coplanars_back);
+    } else {
+      WalkInOrderVisitNodes<ActionHandlerType>(action_handler,
+                                               node,
+                                               node->front_child.get(),
+                                               node->back_child.get(),
+                                               node->coplanars_back,
+                                               node->coplanars_front);
+    }
+  }
+
+  // Returns whether or not nodeA is on one or the other side of nodeB,
+  // coplanar, or whether it crosses nodeB's plane and needs to be split
+  static BspCompareResult GetNodePositionRelative(const DrawPolygon& node_a,
+                                                  const DrawPolygon& node_b);
+  // Returns whether or not our viewer is in front of or behind the plane
+  // defined by this polygon/node
+  static BspCompareResult GetCameraPositionRelative(const DrawPolygon& node);
+};
+
+}  // namespace cc
+
+#endif  // CC_OUTPUT_BSP_TREE_H_
diff --git a/cc/output/bsp_tree_unittest.cc b/cc/output/bsp_tree_unittest.cc
new file mode 100644
index 0000000..100bc91
--- /dev/null
+++ b/cc/output/bsp_tree_unittest.cc
@@ -0,0 +1,348 @@
+// 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 "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "cc/base/scoped_ptr_deque.h"
+#include "cc/base/scoped_ptr_vector.h"
+#include "cc/output/bsp_tree.h"
+#include "cc/output/bsp_walk_action.h"
+#include "cc/quads/draw_polygon.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace cc {
+namespace {
+
+#define EXPECT_SORTED_LISTS_EQ(polygon_list, compare_list)        \
+  do {                                                            \
+    EXPECT_EQ(polygon_list.size(), compare_list.size());          \
+    for (unsigned int i = 0; i < polygon_list.size(); i++) {      \
+      EXPECT_EQ(polygon_list[i]->order_index(), compare_list[i]); \
+    }                                                             \
+  } while (false);
+
+#define INT_VECTOR_FROM_ARRAY(array) \
+  std::vector<int>(array, array + arraysize(array))
+
+#define CREATE_DRAW_POLYGON(vertex_vector, normal, polygon_id) \
+  new DrawPolygon(NULL, vertex_vector, normal, polygon_id)
+
+class BspTreeTest {
+ public:
+  static void RunTest(ScopedPtrDeque<DrawPolygon>* test_polygons,
+                      const std::vector<int>& compare_list) {
+    BspTree bsp_tree(test_polygons);
+
+    std::vector<DrawPolygon*> sorted_list;
+    BspWalkActionToVector action_handler(&sorted_list);
+    bsp_tree.TraverseWithActionHandler(&action_handler);
+
+    EXPECT_SORTED_LISTS_EQ(sorted_list, compare_list);
+    EXPECT_TRUE(VerifySidedness(bsp_tree.root()));
+  }
+
+  static bool VerifySidedness(const scoped_ptr<BspNode>& node) {
+    // We check if both the front and back child nodes have geometry that is
+    // completely on the expected side of the current node.
+    bool front_ok = true;
+    bool back_ok = true;
+    if (node->back_child) {
+      // Make sure the back child lies entirely behind this node.
+      BspCompareResult result = DrawPolygon::SideCompare(
+          *(node->back_child->node_data), *(node->node_data));
+      if (result != BSP_BACK) {
+        return false;
+      }
+      back_ok = VerifySidedness(node->back_child);
+    }
+    // Make sure the front child lies entirely in front of this node.
+    if (node->front_child) {
+      BspCompareResult result = DrawPolygon::SideCompare(
+          *(node->front_child->node_data), *(node->node_data));
+      if (result != BSP_FRONT) {
+        return false;
+      }
+      front_ok = VerifySidedness(node->front_child);
+    }
+    if (!back_ok || !front_ok) {
+      return false;
+    }
+
+    // Now we need to make sure our coplanar geometry is all actually coplanar.
+    for (size_t i = 0; i < node->coplanars_front.size(); i++) {
+      BspCompareResult result = DrawPolygon::SideCompare(
+          *(node->coplanars_front[i]), *(node->node_data));
+      if (result != BSP_COPLANAR_FRONT) {
+        return false;
+      }
+    }
+    for (size_t i = 0; i < node->coplanars_back.size(); i++) {
+      BspCompareResult result = DrawPolygon::SideCompare(
+          *(node->coplanars_back[i]), *(node->node_data));
+      if (result != BSP_COPLANAR_BACK) {
+        return false;
+      }
+    }
+    return true;
+  }
+};
+
+// Simple standing quads all parallel with each other, causing no splits.
+TEST(BspTreeTest, NoSplit) {
+  std::vector<gfx::Point3F> vertices_a;
+  vertices_a.push_back(gfx::Point3F(0.0f, 10.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(0.0f, 0.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(10.0f, 0.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(10.0f, 10.0f, 0.0f));
+  std::vector<gfx::Point3F> vertices_b;
+  vertices_b.push_back(gfx::Point3F(0.0f, 10.0f, -5.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, 0.0f, -5.0f));
+  vertices_b.push_back(gfx::Point3F(10.0f, 0.0f, -5.0f));
+  vertices_b.push_back(gfx::Point3F(10.0f, 10.0f, -5.0f));
+  std::vector<gfx::Point3F> vertices_c;
+  vertices_c.push_back(gfx::Point3F(0.0f, 10.0f, 5.0f));
+  vertices_c.push_back(gfx::Point3F(0.0f, 0.0f, 5.0f));
+  vertices_c.push_back(gfx::Point3F(10.0f, 0.0f, 5.0f));
+  vertices_c.push_back(gfx::Point3F(10.0f, 10.0f, 5.0f));
+
+  scoped_ptr<DrawPolygon> polygon_a(
+      CREATE_DRAW_POLYGON(vertices_a, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 0));
+  scoped_ptr<DrawPolygon> polygon_b(
+      CREATE_DRAW_POLYGON(vertices_b, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 1));
+  scoped_ptr<DrawPolygon> polygon_c(
+      CREATE_DRAW_POLYGON(vertices_c, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 2));
+
+  ScopedPtrDeque<DrawPolygon> polygon_list;
+  polygon_list.push_back(polygon_a.Pass());
+  polygon_list.push_back(polygon_b.Pass());
+  polygon_list.push_back(polygon_c.Pass());
+
+  int compare_ids[] = {1, 0, 2};
+  std::vector<int> compare_list = INT_VECTOR_FROM_ARRAY(compare_ids);
+  BspTreeTest::RunTest(&polygon_list, compare_list);
+}
+
+// Basic two polygon split, can be viewed as a + from above.
+TEST(BspTreeTest, BasicSplit) {
+  std::vector<gfx::Point3F> vertices_a;
+  vertices_a.push_back(gfx::Point3F(-5.0f, -5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(-5.0f, 5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(5.0f, 5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(5.0f, -5.0f, 0.0f));
+  std::vector<gfx::Point3F> vertices_b;
+  vertices_b.push_back(gfx::Point3F(0.0f, -5.0f, -5.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, 5.0f, -5.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, 5.0f, 5.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, -5.0f, 5.0f));
+
+  scoped_ptr<DrawPolygon> polygon_a(
+      CREATE_DRAW_POLYGON(vertices_a, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 0));
+  scoped_ptr<DrawPolygon> polygon_b(
+      CREATE_DRAW_POLYGON(vertices_b, gfx::Vector3dF(-1.0f, 0.0f, 0.0f), 1));
+
+  ScopedPtrDeque<DrawPolygon> polygon_list;
+  polygon_list.push_back(polygon_a.Pass());
+  polygon_list.push_back(polygon_b.Pass());
+
+  int compare_ids[] = {1, 0, 1};
+  std::vector<int> compare_list = INT_VECTOR_FROM_ARRAY(compare_ids);
+  BspTreeTest::RunTest(&polygon_list, compare_list);
+}
+
+// Same as above with the second quad offset so it doesn't intersect. One quad
+// should be very clearly on one side of the other, and no splitting should
+// occur.
+TEST(BspTreeTest, QuadOffset) {
+  std::vector<gfx::Point3F> vertices_a;
+  vertices_a.push_back(gfx::Point3F(-5.0f, -5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(-5.0f, 5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(5.0f, 5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(5.0f, -5.0f, 0.0f));
+  std::vector<gfx::Point3F> vertices_b;
+  vertices_b.push_back(gfx::Point3F(0.0f, 5.0f, -15.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, -5.0f, -15.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, -5.0f, -10.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, 5.0f, -10.0f));
+
+  scoped_ptr<DrawPolygon> polygon_a(
+      CREATE_DRAW_POLYGON(vertices_a, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 0));
+  scoped_ptr<DrawPolygon> polygon_b(
+      CREATE_DRAW_POLYGON(vertices_b, gfx::Vector3dF(-1.0f, 0.0f, 0.0f), 1));
+
+  ScopedPtrDeque<DrawPolygon> polygon_list;
+  polygon_list.push_back(polygon_a.Pass());
+  polygon_list.push_back(polygon_b.Pass());
+
+  int compare_ids[] = {1, 0};
+  std::vector<int> compare_list = INT_VECTOR_FROM_ARRAY(compare_ids);
+  BspTreeTest::RunTest(&polygon_list, compare_list);
+}
+
+// Same as above, but this time we change the order in which the quads are
+// inserted into the tree, causing one to actually cross the plane of the other
+// and cause a split.
+TEST(BspTreeTest, QuadOffsetSplit) {
+  std::vector<gfx::Point3F> vertices_a;
+  vertices_a.push_back(gfx::Point3F(-5.0f, -5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(-5.0f, 5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(5.0f, 5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(5.0f, -5.0f, 0.0f));
+  std::vector<gfx::Point3F> vertices_b;
+  vertices_b.push_back(gfx::Point3F(0.0f, -5.0f, -15.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, 5.0f, -15.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, 5.0f, -10.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, -5.0f, -10.0f));
+
+  scoped_ptr<DrawPolygon> polygon_a(
+      CREATE_DRAW_POLYGON(vertices_a, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 0));
+  scoped_ptr<DrawPolygon> polygon_b(
+      CREATE_DRAW_POLYGON(vertices_b, gfx::Vector3dF(-1.0f, 0.0f, 0.0f), 1));
+
+  ScopedPtrDeque<DrawPolygon> polygon_list;
+  polygon_list.push_back(polygon_b.Pass());
+  polygon_list.push_back(polygon_a.Pass());
+
+  int compare_ids[] = {0, 1, 0};
+  std::vector<int> compare_list = INT_VECTOR_FROM_ARRAY(compare_ids);
+  BspTreeTest::RunTest(&polygon_list, compare_list);
+}
+
+// In addition to what can be viewed as a + from above, another piece of
+// geometry is inserted to cut these pieces right in the middle, viewed as
+// a quad from overhead.
+TEST(BspTreeTest, ThreeWaySplit) {
+  std::vector<gfx::Point3F> vertices_a;
+  vertices_a.push_back(gfx::Point3F(-5.0f, -5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(-5.0f, 5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(5.0f, 5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(5.0f, -5.0f, 0.0f));
+  std::vector<gfx::Point3F> vertices_b;
+  vertices_b.push_back(gfx::Point3F(0.0f, -5.0f, -5.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, 5.0f, -5.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, 5.0f, 5.0f));
+  vertices_b.push_back(gfx::Point3F(0.0f, -5.0f, 5.0f));
+  std::vector<gfx::Point3F> vertices_c;
+  vertices_c.push_back(gfx::Point3F(-5.0f, 0.0f, -5.0f));
+  vertices_c.push_back(gfx::Point3F(-5.0f, 0.0f, 5.0f));
+  vertices_c.push_back(gfx::Point3F(5.0f, 0.0f, 5.0f));
+  vertices_c.push_back(gfx::Point3F(5.0f, 0.0f, -5.0f));
+
+  scoped_ptr<DrawPolygon> polygon_a(
+      CREATE_DRAW_POLYGON(vertices_a, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 0));
+  scoped_ptr<DrawPolygon> polygon_b(
+      CREATE_DRAW_POLYGON(vertices_b, gfx::Vector3dF(-1.0f, 0.0f, 0.0f), 1));
+  scoped_ptr<DrawPolygon> polygon_c(
+      CREATE_DRAW_POLYGON(vertices_c, gfx::Vector3dF(0.0f, 1.0f, 0.0f), 2));
+
+  ScopedPtrDeque<DrawPolygon> polygon_list;
+  polygon_list.push_back(polygon_a.Pass());
+  polygon_list.push_back(polygon_b.Pass());
+  polygon_list.push_back(polygon_c.Pass());
+
+  int compare_ids[] = {2, 1, 2, 0, 2, 1, 2};
+  std::vector<int> compare_list = INT_VECTOR_FROM_ARRAY(compare_ids);
+  BspTreeTest::RunTest(&polygon_list, compare_list);
+}
+
+// This test checks whether coplanar geometry, when inserted into the tree in
+// order, comes back in the same order as it should.
+TEST(BspTreeTest, Coplanar) {
+  std::vector<gfx::Point3F> vertices_a;
+  vertices_a.push_back(gfx::Point3F(-5.0f, -5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(-5.0f, 5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(5.0f, 5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(5.0f, -5.0f, 0.0f));
+  std::vector<gfx::Point3F> vertices_b;
+  vertices_b.push_back(gfx::Point3F(-4.0f, -4.0f, 0.0f));
+  vertices_b.push_back(gfx::Point3F(-4.0f, 4.0f, 0.0f));
+  vertices_b.push_back(gfx::Point3F(4.0f, 4.0f, 0.0f));
+  vertices_b.push_back(gfx::Point3F(4.0f, -4.0f, 0.0f));
+  std::vector<gfx::Point3F> vertices_c;
+  vertices_c.push_back(gfx::Point3F(-3.0f, -3.0f, 0.0f));
+  vertices_c.push_back(gfx::Point3F(-3.0f, 3.0f, 0.0f));
+  vertices_c.push_back(gfx::Point3F(3.0f, 3.0f, 0.0f));
+  vertices_c.push_back(gfx::Point3F(3.0f, -3.0f, 0.0f));
+
+  scoped_ptr<DrawPolygon> polygon_a(
+      CREATE_DRAW_POLYGON(vertices_a, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 0));
+  scoped_ptr<DrawPolygon> polygon_b(
+      CREATE_DRAW_POLYGON(vertices_b, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 1));
+  scoped_ptr<DrawPolygon> polygon_c(
+      CREATE_DRAW_POLYGON(vertices_c, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 2));
+
+  scoped_ptr<DrawPolygon> polygon_d = polygon_a->CreateCopy();
+  scoped_ptr<DrawPolygon> polygon_e = polygon_b->CreateCopy();
+  scoped_ptr<DrawPolygon> polygon_f = polygon_c->CreateCopy();
+
+  {
+    ScopedPtrDeque<DrawPolygon> polygon_list;
+    polygon_list.push_back(polygon_a.Pass());
+    polygon_list.push_back(polygon_b.Pass());
+    polygon_list.push_back(polygon_c.Pass());
+
+    int compare_ids[] = {0, 1, 2};
+    std::vector<int> compare_list = INT_VECTOR_FROM_ARRAY(compare_ids);
+    BspTreeTest::RunTest(&polygon_list, compare_list);
+  }
+
+  // Now check a different order and ensure we get that back as well
+  {
+    ScopedPtrDeque<DrawPolygon> polygon_list;
+    polygon_list.push_back(polygon_f.Pass());
+    polygon_list.push_back(polygon_d.Pass());
+    polygon_list.push_back(polygon_e.Pass());
+
+    int compare_ids[] = {0, 1, 2};
+    std::vector<int> compare_list = INT_VECTOR_FROM_ARRAY(compare_ids);
+    BspTreeTest::RunTest(&polygon_list, compare_list);
+  }
+}
+
+// A bunch of coplanar geometry should end up sharing a single node, and
+// result in the final piece of geometry splitting into just two pieces on
+// either side of the shared plane.
+TEST(BspTreeTest, CoplanarSplit) {
+  std::vector<gfx::Point3F> vertices_a;
+  vertices_a.push_back(gfx::Point3F(-5.0f, -5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(-5.0f, 5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(5.0f, 5.0f, 0.0f));
+  vertices_a.push_back(gfx::Point3F(5.0f, -5.0f, 0.0f));
+  std::vector<gfx::Point3F> vertices_b;
+  vertices_b.push_back(gfx::Point3F(-4.0f, -4.0f, 0.0f));
+  vertices_b.push_back(gfx::Point3F(-4.0f, 4.0f, 0.0f));
+  vertices_b.push_back(gfx::Point3F(4.0f, 4.0f, 0.0f));
+  vertices_b.push_back(gfx::Point3F(4.0f, -4.0f, 0.0f));
+  std::vector<gfx::Point3F> vertices_c;
+  vertices_c.push_back(gfx::Point3F(-3.0f, -3.0f, 0.0f));
+  vertices_c.push_back(gfx::Point3F(-3.0f, 3.0f, 0.0f));
+  vertices_c.push_back(gfx::Point3F(3.0f, 3.0f, 0.0f));
+  vertices_c.push_back(gfx::Point3F(3.0f, -3.0f, 0.0f));
+  std::vector<gfx::Point3F> vertices_d;
+  vertices_d.push_back(gfx::Point3F(0.0f, -15.0f, -15.0f));
+  vertices_d.push_back(gfx::Point3F(0.0f, 15.0f, -15.0f));
+  vertices_d.push_back(gfx::Point3F(0.0f, 15.0f, 15.0f));
+  vertices_d.push_back(gfx::Point3F(0.0f, -15.0f, 15.0f));
+
+  scoped_ptr<DrawPolygon> polygon_a(
+      CREATE_DRAW_POLYGON(vertices_a, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 0));
+  scoped_ptr<DrawPolygon> polygon_b(
+      CREATE_DRAW_POLYGON(vertices_b, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 1));
+  scoped_ptr<DrawPolygon> polygon_c(
+      CREATE_DRAW_POLYGON(vertices_c, gfx::Vector3dF(0.0f, 0.0f, 1.0f), 2));
+  scoped_ptr<DrawPolygon> polygon_d(
+      CREATE_DRAW_POLYGON(vertices_d, gfx::Vector3dF(-1.0f, 0.0f, 0.0f), 3));
+
+  ScopedPtrDeque<DrawPolygon> polygon_list;
+  polygon_list.push_back(polygon_a.Pass());
+  polygon_list.push_back(polygon_b.Pass());
+  polygon_list.push_back(polygon_c.Pass());
+  polygon_list.push_back(polygon_d.Pass());
+
+  int compare_ids[] = {3, 0, 1, 2, 3};
+  std::vector<int> compare_list = INT_VECTOR_FROM_ARRAY(compare_ids);
+  BspTreeTest::RunTest(&polygon_list, compare_list);
+}
+
+}  // namespace
+}  // namespace cc
diff --git a/cc/output/bsp_walk_action.cc b/cc/output/bsp_walk_action.cc
new file mode 100644
index 0000000..da5ada5
--- /dev/null
+++ b/cc/output/bsp_walk_action.cc
@@ -0,0 +1,23 @@
+// 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/output/bsp_walk_action.h"
+
+#include <vector>
+
+#include "base/memory/scoped_ptr.h"
+#include "cc/output/direct_renderer.h"
+#include "cc/quads/draw_polygon.h"
+
+namespace cc {
+
+void BspWalkActionToVector::operator()(DrawPolygon* item) {
+  list_->push_back(item);
+}
+
+BspWalkActionToVector::BspWalkActionToVector(std::vector<DrawPolygon*>* in_list)
+    : list_(in_list) {
+}
+
+}  // namespace cc
diff --git a/cc/output/bsp_walk_action.h b/cc/output/bsp_walk_action.h
new file mode 100644
index 0000000..bb31865
--- /dev/null
+++ b/cc/output/bsp_walk_action.h
@@ -0,0 +1,34 @@
+// 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.
+
+#ifndef CC_OUTPUT_BSP_WALK_ACTION_H_
+#define CC_OUTPUT_BSP_WALK_ACTION_H_
+
+#include <vector>
+
+#include "base/memory/scoped_ptr.h"
+#include "cc/output/direct_renderer.h"
+#include "cc/quads/draw_polygon.h"
+
+namespace cc {
+
+class CC_EXPORT BspWalkAction {
+ public:
+  virtual void operator()(DrawPolygon* item) = 0;
+};
+
+// The BspTree class takes ownership of all the DrawPolygons returned in list_
+// so the BspTree must be preserved while elements in that vector are in use.
+class CC_EXPORT BspWalkActionToVector : public BspWalkAction {
+ public:
+  explicit BspWalkActionToVector(std::vector<DrawPolygon*>* in_list);
+  virtual void operator()(DrawPolygon* item) OVERRIDE;
+
+ private:
+  std::vector<DrawPolygon*>* list_;
+};
+
+}  // namespace cc
+
+#endif  // CC_OUTPUT_BSP_WALK_ACTION_H_