WIP BSP Tree for 3D Layer Sorting

cc/output/bsp_tree.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/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