cc: Change RTree nodes container to be a vector (with reserve).

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), nodes_(sizeof(Node)) {}
+RTree::RTree() : num_data_elements_(0u) {}
 
 RTree::~RTree() {}
 
 RTree::Node* RTree::AllocateNodeAtLevel(int level) {
-  Node& node = nodes_.AllocateAndConstruct<Node>();
+  // 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() / MAX_CHILDREN);
-  int remainder = static_cast<int>(branches->size() % MAX_CHILDREN);
+  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 >= MIN_CHILDREN)
+    if (remainder >= kMinChildren)
       remainder = 0;
     else
-      remainder = MIN_CHILDREN - remainder;
+      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 = MAX_CHILDREN;
+      int increment_by = kMaxChildren;
       if (remainder != 0) {
         // if need be, omit some nodes to make up for remainder
-        if (remainder <= MAX_CHILDREN - MIN_CHILDREN) {
+        if (remainder <= kMaxChildren - kMinChildren) {
           increment_by -= remainder;
           remainder = 0;
         } else {
-          increment_by = MIN_CHILDREN;
-          remainder -= MAX_CHILDREN - MIN_CHILDREN;
+          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;
@@ skipping 44 matching lines @@
         SearchRecursive(node->children[i].subtree, query, results);
     }
   }
 }
 
 gfx::Rect RTree::GetBounds() const {
   return root_.bounds;
 }
 
 }  // namespace cc