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// 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 "ui/accessibility/tree_generator.h"
#include "ui/accessibility/ax_serializable_tree.h"
#include "ui/accessibility/ax_tree.h"
namespace ui {
static int UniqueTreeCountForNodeCount(int node_count,
bool permutations) {
int unique_tree_count = 1;
// (n-1)! for the possible trees.
for (int i = 2; i < node_count; ++i)
unique_tree_count *= i;
// n! for the permutations of ids.
if (permutations)
unique_tree_count = unique_tree_count * unique_tree_count * node_count;
return unique_tree_count;
}
TreeGenerator::TreeGenerator(int max_node_count, bool permutations)
: max_node_count_(max_node_count),
permutations_(permutations),
total_unique_tree_count_(0) {
unique_tree_count_by_size_.push_back(0);
for (int i = 1; i <= max_node_count; ++i) {
int unique_tree_count = UniqueTreeCountForNodeCount(i, permutations);
unique_tree_count_by_size_.push_back(unique_tree_count);
total_unique_tree_count_ += unique_tree_count;
}
}
TreeGenerator::~TreeGenerator() {
}
int TreeGenerator::UniqueTreeCount() const {
return total_unique_tree_count_;
}
void TreeGenerator::BuildUniqueTree(int tree_index, AXTree* out_tree) const {
CHECK_LT(tree_index, total_unique_tree_count_);
int unique_tree_count_so_far = 0;
for (int node_count = 1; node_count <= max_node_count_; ++node_count) {
int unique_tree_count = unique_tree_count_by_size_[node_count];
if (tree_index - unique_tree_count_so_far < unique_tree_count) {
BuildUniqueTreeWithSize(node_count,
tree_index - unique_tree_count_so_far,
out_tree);
return;
}
unique_tree_count_so_far += unique_tree_count;
}
}
void TreeGenerator::BuildUniqueTreeWithSize(
int node_count, int tree_index, AXTree* out_tree) const {
std::vector<int> indices;
std::vector<int> permuted;
int unique_tree_count = unique_tree_count_by_size_[node_count];
CHECK_LT(tree_index, unique_tree_count);
if (permutations_) {
// Use the first few bits of |tree_index| to permute the indices.
for (int i = 0; i < node_count; ++i)
indices.push_back(i + 1);
for (int i = 0; i < node_count; ++i) {
int p = (node_count - i);
int index = tree_index % p;
tree_index /= p;
permuted.push_back(indices[index]);
indices.erase(indices.begin() + index);
}
} else {
for (int i = 0; i < node_count; ++i)
permuted.push_back(i + 1);
}
// Build an AXTreeUpdate. The first two nodes of the tree always
// go in the same place.
AXTreeUpdate update;
update.root_id = permuted[0];
update.nodes.resize(node_count);
update.nodes[0].id = permuted[0];
if (node_count > 1) {
update.nodes[0].child_ids.push_back(permuted[1]);
update.nodes[1].id = permuted[1];
}
// The remaining nodes are assigned based on their parent
// selected from the next bits from |tree_index|.
for (int i = 2; i < node_count; ++i) {
update.nodes[i].id = permuted[i];
int parent_index = (tree_index % i);
tree_index /= i;
update.nodes[parent_index].child_ids.push_back(permuted[i]);
}
// Unserialize the tree update into the destination tree.
CHECK(out_tree->Unserialize(update)) << out_tree->error();
};
} // namespace ui
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