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// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "ui/accessibility/ax_tree_update_util.h"
#include "base/metrics/histogram_macros.h"
#include "ui/accessibility/ax_tree_update.h"
namespace ui {
// Two tree updates can be merged into one if the second one
// doesn't clear a subtree, doesn't have new tree data, and
// doesn't have a new root id - in other words the second tree
// update consists of only changes to nodes.
bool AXTreeUpdatesCanBeMerged(const AXTreeUpdate& u1, const AXTreeUpdate& u2) {
if (u2.node_id_to_clear)
return false;
if (u2.has_tree_data && u2.tree_data != u1.tree_data)
return false;
if (u2.root_id != u1.root_id)
return false;
return true;
}
bool MergeAXTreeUpdates(std::vector<AXTreeUpdate>& src,
std::vector<AXTreeUpdate>* dst) {
SCOPED_UMA_HISTOGRAM_TIMER_MICROS(
"Accessibility.Performance.MergeAXTreeUpdates");
size_t merge_count = 0;
for (size_t i = 1; i < src.size(); i++) {
if (AXTreeUpdatesCanBeMerged(src[i - 1], src[i]))
merge_count++;
}
// Doing a single merge isn't necessarily worth it because
// copying the tree updates takes time too so the total
// savings is less. But two more more merges is probably
// worth the overhead of copying.
if (merge_count < 2)
return false;
dst->resize(src.size() - merge_count);
(*dst)[0] = std::move(src[0]);
size_t dst_index = 0;
for (size_t i = 1; i < src.size(); i++) {
// Use (*dst)[dst_index] over src[i-1] for the merge because src[i-1] may
// be in an undetermined state after being merged.
if (AXTreeUpdatesCanBeMerged((*dst)[dst_index], src[i])) {
std::vector<AXNodeData>& dst_nodes = (*dst)[dst_index].nodes;
std::vector<AXNodeData>& src_nodes = src[i].nodes;
for (auto& src_node : src_nodes) {
dst_nodes.emplace_back(src_node);
}
} else {
dst_index++;
(*dst)[dst_index] = src[i];
}
}
return true;
}
} // namespace ui
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