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/output/bsp_controller.h"
+#include "cc/quads/draw_polygon.h"
+
+namespace cc {
+
+BspNode::BspNode(scoped_ptr<DrawPolygon> data) {
+  node_data = data.Pass();
+}
+
+BspNode::~BspNode() {
+}
+
+BspTree::BspTree(BspController* bsp_controller,
+                 ScopedPtrVector<DrawPolygon>* list)
+    : controller_(bsp_controller) {
+  FromList(list);
+}
+
+// FromList takes an input list and moves the better splitting polygons to the
+// front of the queue so when it comes time to build the tree, we already have
+// our splitting plane decided in the first element of the queue. BuildTree is
+// then called to perform the actual building of the tree using this list.
+void BspTree::FromList(ScopedPtrVector<DrawPolygon>* list) {
+  if (list->size() == 0)
+    return;
+
+  float max_weight = 0.0f;
+  ScopedPtrDeque<DrawPolygon> list_data;
+  for (ScopedPtrVector<DrawPolygon>::iterator it = list->begin();
+       it != list->end();
+       ++it) {
+    float poly_weight = controller_->SplitWeight(*list->back());
+    if (poly_weight > max_weight) {
+      list_data.push_front(list->take(it));
+      max_weight = poly_weight;
+    } else {
+      list_data.push_back(list->take(it));
+    }
+  }
+
+  root_ = scoped_ptr<BspNode>(new BspNode(list_data.take_front()));
+  BuildTree(root_, &list_data);
+}
+
+static void UpdateNodeListAndMaxWeight(float new_weight,
+                                       float* current_max_weight,
+                                       ScopedPtrDeque<DrawPolygon>* list,
+                                       scoped_ptr<DrawPolygon> node_data) {
+  if (new_weight > *current_max_weight) {
+    list->push_front(node_data.Pass());
+    *current_max_weight = new_weight;
+  } else {
+    list->push_back(node_data.Pass());
+  }
+}
+
+// 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(const scoped_ptr<BspNode>& node,
+                        ScopedPtrDeque<DrawPolygon>* data) {
+  ScopedPtrDeque<DrawPolygon> front_list;
+  ScopedPtrDeque<DrawPolygon> back_list;
+  // We keep track of the splitting weights (the "score" of a polygon that
+  // chooses whether or not it's the splitting plane of a new node) for both
+  // the front and back list independently so the better splitting plane is
+  // chosen for both sides.
+  float max_front_weight = 0.0f;
+  float max_back_weight = 0.0f;
+
+  // 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 (data->size() > 0) {
+    // Is this particular polygon in front of or behind our splitting polygon.
+    BspCompareResult comparer_result = controller_->GetNodePositionRelative(
+        *data->front(), *(node->node_data));
+    float poly_weight = controller_->SplitWeight(*data->front());
+
+    // 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.
+    scoped_ptr<DrawPolygon> new_front;
+    scoped_ptr<DrawPolygon> new_back;
+    float front_poly_weight = 0.0f;
+    float back_poly_weight = 0.0f;
+    switch (comparer_result) {
+      case BSP_FRONT:
+        UpdateNodeListAndMaxWeight(poly_weight,
+                                   &max_front_weight,
+                                   &front_list,
+                                   data->take_front().Pass());
+        break;
+      case BSP_BACK:
+        UpdateNodeListAndMaxWeight(poly_weight,
+                                   &max_back_weight,
+                                   &back_list,
+                                   data->take_front().Pass());
+        break;
+      case BSP_SPLIT:
+        // Time to split this geometry, *it needs to be split by node_data.
+        if (controller_->SplitPolygon(data->take_front(),
+                                      *(node->node_data),
+                                      &new_front,
+                                      &new_back)) {
+          // Now add new_front and new_back to their respective lists, again
+          // using the heuristic in an attempt to choose the best splitting
+          // plane, and keep track of the highest weighted polygon known so far
+          // so if we find something better we can use that instead.
+          front_poly_weight = controller_->SplitWeight(*new_front);
+          back_poly_weight = controller_->SplitWeight(*new_back);
+
+          UpdateNodeListAndMaxWeight(front_poly_weight,
+                                     &max_front_weight,
+                                     &front_list,
+                                     new_front.Pass());
+          UpdateNodeListAndMaxWeight(
+              back_poly_weight, &max_back_weight, &back_list, new_back.Pass());
+        }
+        break;
+      case BSP_COPLANAR_FRONT:
+        node->coplanars_front.push_back(data->take_front());
+        break;
+      case BSP_COPLANAR_BACK:
+        node->coplanars_back.push_back(data->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, &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, &front_list);
+  }
+}
+
+void BspTree::Clear() {
+  if (root_) {
+    root_.reset();
+  }
+}
+
+BspTree::~BspTree() {
+  Clear();
+}
+
+}  // namespace cc