cc/base/rtree.cc

// Copyright (c) 2015 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/rtree.h"

#include <stddef.h>
#include <stdint.h>

#include <algorithm>
#include <cmath>

#include "base/logging.h"
#include "base/numerics/saturated_arithmetic.h"

namespace cc {

RTree::RTree() : num_data_elements_(0u) {}

RTree::~RTree() {}

RTree::Node* RTree::AllocateNodeAtLevel(int level) {
  // We don't allow reallocations, since that would invalidate references to
  // existing nodes, so verify that capacity > size.
  DCHECK_GT(nodes_.capacity(), nodes_.size());
  nodes_.emplace_back();
  Node& node = nodes_.back();
  node.num_children = 0;
  node.level = level;
  return &node;
}

RTree::Branch RTree::BuildRecursive(std::vector<Branch>* branches, int level) {
  // Only one branch.  It will be the root.
  if (branches->size() == 1)
    return (*branches)[0];

  // TODO(vmpstr): Investigate if branches should be sorted in y.
  // The comment from Skia reads:
  // We might sort our branches here, but we expect Blink gives us a reasonable
  // x,y order. Skipping a call to sort (in Y) here resulted in a 17% win for
  // recording with negligible difference in playback speed.
  int num_branches = static_cast<int>(branches->size() / kMaxChildren);
  int remainder = static_cast<int>(branches->size() % kMaxChildren);

  if (remainder > 0) {
    ++num_branches;
    // If the remainder isn't enough to fill a node, we'll add fewer nodes to
    // other branches.
    if (remainder >= kMinChildren)
      remainder = 0;
    else
      remainder = kMinChildren - remainder;
  }

  int num_strips = static_cast<int>(std::ceil(std::sqrt(num_branches)));
  int num_tiles = static_cast<int>(
      std::ceil(num_branches / static_cast<float>(num_strips)));
  size_t current_branch = 0;

  size_t new_branch_index = 0;
  for (int i = 0; i < num_strips; ++i) {
    // Might be worth sorting by X here too.
    for (int j = 0; j < num_tiles && current_branch < branches->size(); ++j) {
      int increment_by = kMaxChildren;
      if (remainder != 0) {
        // if need be, omit some nodes to make up for remainder
        if (remainder <= kMaxChildren - kMinChildren) {
          increment_by -= remainder;
          remainder = 0;
        } else {
          increment_by = kMinChildren;
          remainder -= kMaxChildren - kMinChildren;
        }
      }
      Node* node = AllocateNodeAtLevel(level);
      node->num_children = 1;
      node->children[0] = (*branches)[current_branch];

      Branch branch;
      branch.bounds = (*branches)[current_branch].bounds;
      branch.subtree = node;
      ++current_branch;
      int x = branch.bounds.x();
      int y = branch.bounds.y();
      int right = branch.bounds.right();
      int bottom = branch.bounds.bottom();
      for (int k = 1; k < increment_by && current_branch < branches->size();
           ++k) {
        // We use a custom union instead of gfx::Rect::Union here, since this
        // bypasses some empty checks and extra setters, which improves
        // performance.
        auto& bounds = (*branches)[current_branch].bounds;
        x = std::min(x, bounds.x());
        y = std::min(y, bounds.y());
        right = std::max(right, bounds.right());
        bottom = std::max(bottom, bounds.bottom());

        node->children[k] = (*branches)[current_branch];
        ++node->num_children;
        ++current_branch;
      }
      branch.bounds.SetRect(x, y, base::SaturatedSubtraction(right, x),
                            base::SaturatedSubtraction(bottom, y));

      DCHECK_LT(new_branch_index, current_branch);
      (*branches)[new_branch_index] = branch;
      ++new_branch_index;
    }
  }
  branches->resize(new_branch_index);
  return BuildRecursive(branches, level + 1);
}

void RTree::Search(const gfx::Rect& query, std::vector<size_t>* results) const {
  if (num_data_elements_ > 0 && query.Intersects(root_.bounds))
    SearchRecursive(root_.subtree, query, results);
}

void RTree::SearchRecursive(Node* node,
                            const gfx::Rect& query,
                            std::vector<size_t>* results) const {
  for (uint16_t i = 0; i < node->num_children; ++i) {
    if (query.Intersects(node->children[i].bounds)) {
      if (node->level == 0)
        results->push_back(node->children[i].index);
      else
        SearchRecursive(node->children[i].subtree, query, results);
    }
  }
}

gfx::Rect RTree::GetBounds() const {
  return root_.bounds;
}

}  // namespace cc