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);
+}
+
+void BspTree::FromList(ScopedPtrVector<DrawPolygon>* list) {
+  if (list->size() <= 0)

[Ian Vollick, 2014/07/16 20:54:32]

Can size < 0?

[troyhildebrandt, 2014/07/18 21:48:26]

Nope, it's unsigned, changed to == 0.

+    return;
+
+  float split_weight = 0.0f;

[Ian Vollick, 2014/07/16 20:54:33]

nit: max_weight or max_split_weight conveys a bit more meaning.

[troyhildebrandt, 2014/07/18 21:48:25]

Done.

+  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 > split_weight) {
+      list_data.push_front(list->take(it));
+      split_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);
+}
+
+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 front_weight = 0.0f;

[Ian Vollick, 2014/07/16 20:54:32]

Could you choose names for these that involve "max"? As above, I find
front_weight and back_weight don't convey a whole lot of meaning.

[troyhildebrandt, 2014/07/18 21:48:26]

Done.

+  float 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.
+    if (comparer_result == BSP_FRONT) {

[Ian Vollick, 2014/07/16 20:54:32]

switch?

[troyhildebrandt, 2014/07/18 21:48:26]

Done.

+      if (poly_weight > front_weight) {
+        front_list.push_front(data->take_front());
+        front_weight = poly_weight;
+      } else {
+        front_list.push_back(data->take_front());
+      }
+
+    } else if (comparer_result == BSP_BACK) {
+      if (poly_weight > back_weight) {
+        back_list.push_front(data->take_front());
+        back_weight = poly_weight;
+      } else {
+        back_list.push_back(data->take_front());

[Ian Vollick, 2014/07/16 20:54:33]

The front and back behavior is so symmetric that it makes me think that a helper
fn taking ptrs to the appropriate stuff could be used instead of duplicating the
logic.

[troyhildebrandt, 2014/07/18 21:48:26]

Done.

+      }
+
+    } else if (comparer_result == BSP_SPLIT) {
+      // Time to split this geometry, *it needs to be split by node_data.
+      scoped_ptr<DrawPolygon> new_front;
+      scoped_ptr<DrawPolygon> new_back;
+      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.
+        float front_poly_weight = controller_->SplitWeight(*new_front);
+        float back_poly_weight = controller_->SplitWeight(*new_back);
+
+        if (front_poly_weight > front_weight) {
+          front_list.push_front(new_front.Pass());
+          front_weight = front_poly_weight;
+        } else {
+          front_list.push_back(new_front.Pass());

[Ian Vollick, 2014/07/16 20:54:32]

These two bits could use that helper, too.

[troyhildebrandt, 2014/07/18 21:48:26]

Done.

+        }
+
+        if (back_poly_weight > back_weight) {
+          back_list.push_front(new_back.Pass());
+          back_weight = back_poly_weight;
+        } else {
+          back_list.push_back(new_back.Pass());
+        }
+      }
+    } else if (comparer_result == BSP_COPLANAR_FRONT) {
+      node->coplanars_front.push_back(data->take_front());
+    } else if (comparer_result == BSP_COPLANAR_BACK) {
+      node->coplanars_back.push_back(data->take_front());
+    }

[Ian Vollick, 2014/07/16 20:54:33]

else {
  NOTREACHED(); // or equivalent for the default: case if you switch to switch.
}

[troyhildebrandt, 2014/07/18 21:48:26]

Done.

+  }
+
+  // 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