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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.
#ifndef UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_BUFFER_H_
#define UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_BUFFER_H_
#include "base/memory/scoped_ptr.h"
#include "base/memory/scoped_vector.h"
#include "base/time/time.h"
#include "ui/events/gesture_detection/gesture_detection_export.h"
namespace ui {
class MotionEvent;
// Allows event forwarding and flush requests from a |MotionEventBuffer|.
class MotionEventBufferClient {
public:
virtual ~MotionEventBufferClient() {}
virtual void ForwardMotionEvent(const MotionEvent& event) = 0;
virtual void SetNeedsFlush() = 0;
};
// Utility class for buffering streamed MotionEventVector until a given flush.
// Events that can be combined will remain buffered, and depending on the flush
// time and buffered events, a resampled event with history will be synthesized.
// The primary purpose of this class is to ensure a smooth output motion signal
// by resampling a discrete input signal that may run on a different frequency
// or lack alignment with the output display signal.
// Note that this class is largely based on code from Android's existing touch
// pipeline (in particular, logic from ImageTransport, http://goo.gl/Ixsb0D).
// See the design doc at http://goo.gl/MdmpCf for more details.
class GESTURE_DETECTION_EXPORT MotionEventBuffer {
public:
// The provided |client| must not be null, and |enable_resampling| determines
// resampling behavior (see |resample_|).
MotionEventBuffer(MotionEventBufferClient* client, bool enable_resampling);
~MotionEventBuffer();
// Should be called upon receipt of an event from the platform, prior to event
// dispatch to UI or content components. Events that can be coalesced will
// remain buffered until the next |Flush()|, while other events will be
// forwarded immediately (incidentally flushing currently buffered events).
void OnMotionEvent(const MotionEvent& event);
// Forward any buffered events, resampling if necessary (see |resample_|)
// according to the provided |frame_time|. This should be called in response
// to |SetNeedsFlush()| calls on the client. If the buffer is empty, no
// events will be forwarded, and if another flush is necessary it will be
// requested.
void Flush(base::TimeTicks frame_time);
private:
typedef ScopedVector<MotionEvent> MotionEventVector;
void FlushWithoutResampling(MotionEventVector events);
MotionEventBufferClient* const client_;
MotionEventVector buffered_events_;
// Time of the most recently extrapolated event. This will be 0 if the
// last sent event was not extrapolated. Used internally to guard against
// conflicts between events received from the platfrom that may have an
// earlier timestamp than that synthesized at the latest resample.
base::TimeTicks last_extrapolated_event_time_;
// Whether buffered events should be resampled upon |Flush()|. If true, short
// horizon interpolation/extrapolation will be used to synthesize the
// forwarded event. Otherwise the most recently buffered event will be
// forwarded, with preceding events as historical entries. Defaults to true.
bool resample_;
DISALLOW_COPY_AND_ASSIGN(MotionEventBuffer);
};
} // namespace ui
#endif // UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_BUFFER_H_
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