chromium/components/input/mouse_wheel_event_queue.h

// Copyright 2016 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_INPUT_MOUSE_WHEEL_EVENT_QUEUE_H_
#define COMPONENTS_INPUT_MOUSE_WHEEL_EVENT_QUEUE_H_

#include <memory>

#include "base/containers/circular_deque.h"
#include "base/functional/callback.h"
#include "base/memory/raw_ptr.h"
#include "base/trace_event/trace_event.h"
#include "components/input/event_with_latency_info.h"
#include "base/component_export.h"
#include "third_party/blink/public/common/input/web_input_event.h"
#include "third_party/blink/public/mojom/input/input_event_result.mojom-shared.h"

namespace input {

// This class represents a single queued mouse wheel event. Its main use
// is that it is reported via trace events.
class QueuedWebMouseWheelEvent : public MouseWheelEventWithLatencyInfo { … };

// Interface with which MouseWheelEventQueue can forward mouse wheel events,
// and dispatch mouse wheel event responses.
class COMPONENT_EXPORT(INPUT) MouseWheelEventQueueClient { … };

// A queue for throttling and coalescing mouse wheel events. This class tracks
// wheel events sent to the renderer and receives their ACKs. If the ACK
// reports the event went unconsumed by the renderer, this class will generate
// a sequence of gesture scroll events.
//
// Within a sequence, wheel events are initially forwarded using a blocking
// dispatch. This means that further wheel events are queued and scroll event
// generation will wait (i.e.  block) until the in-flight wheel event is ACKed.
// Once a wheel event goes unconsumed, and scrolling begins, dispatch of
// subsequent wheel events becomes non-blocking. This means the wheel event
// will be ACKed by the browser immediately after being dispatched. This will
// cause scroll events to follow the wheel immediately and new wheel events
// will be dispatched immediately rather than queueing.
class COMPONENT_EXPORT(INPUT) MouseWheelEventQueue { … };

}  // namespace input

#endif  // COMPONENTS_INPUT_MOUSE_WHEEL_EVENT_QUEUE_H_