chromium/third_party/blink/renderer/core/layout/hit_test_cache.h

// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_HIT_TEST_CACHE_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_HIT_TEST_CACHE_H_

#include "third_party/blink/renderer/core/core_export.h"
#include "third_party/blink/renderer/core/layout/hit_test_location.h"
#include "third_party/blink/renderer/core/layout/hit_test_result.h"
#include "third_party/blink/renderer/platform/heap/collection_support/heap_vector.h"
#include "third_party/blink/renderer/platform/heap/garbage_collected.h"
#include "third_party/blink/renderer/platform/wtf/vector.h"

namespace blink {

// This object implements a cache for storing successful hit tests to DOM nodes
// in the visible viewport. The cache is cleared on dom modifications,
// scrolling, CSS style modifications.
//
// Multiple hit tests can occur when processing events. Typically the DOM
// doesn't change when each event is processed so in order to decrease the time
// spent processing the events a hit cache is useful. For example a GestureTap
// event will generate a series of simulated mouse events (move, down, up,
// click) with the same co-ordinates and ideally we'd like to do the hit test
// once and use the result for the targetting of each event.
//
// Some of the related design, motivation can be found in:
// https://docs.google.com/document/d/1b0NYAD4S9BJIpHGa4JD2HLmW28f2rUh1jlqrgpU3zVU/
//

// A cache size of 2 is used because it is relatively cheap to store;
// and the ping-pong behaviour of some of the HitTestRequest flags during
// Mouse/Touch/Pointer events can generate increased cache misses with
// size of 1.
#define HIT_TEST_CACHE_SIZE …

struct HitTestCacheEntry { … };

class CORE_EXPORT HitTestCache final : public GarbageCollected<HitTestCache> { … };

}  // namespace blink

WTF_ALLOW_CLEAR_UNUSED_SLOTS_WITH_MEM_FUNCTIONS(…)

#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_LAYOUT_HIT_TEST_CACHE_H_