1 // Copyright 2014 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_BUFFER_H_ 6 #define UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_BUFFER_H_ 7 8 #include "base/memory/scoped_ptr.h" 9 #include "base/memory/scoped_vector.h" 10 #include "base/time/time.h" 11 #include "ui/events/gesture_detection/gesture_detection_export.h" 12 13 namespace ui { 14 15 class MotionEvent; 16 17 // Allows event forwarding and flush requests from a |MotionEventBuffer|. 18 class MotionEventBufferClient { 19 public: 20 virtual ~MotionEventBufferClient() {} 21 virtual void ForwardMotionEvent(const MotionEvent& event) = 0; 22 virtual void SetNeedsFlush() = 0; 23 }; 24 25 // Utility class for buffering streamed MotionEventVector until a given flush. 26 // Events that can be combined will remain buffered, and depending on the flush 27 // time and buffered events, a resampled event with history will be synthesized. 28 // The primary purpose of this class is to ensure a smooth output motion signal 29 // by resampling a discrete input signal that may run on a different frequency 30 // or lack alignment with the output display signal. 31 // Note that this class is largely based on code from Android's existing touch 32 // pipeline (in particular, logic from ImageTransport, http://goo.gl/Ixsb0D). 33 // See the design doc at http://goo.gl/MdmpCf for more details. 34 class GESTURE_DETECTION_EXPORT MotionEventBuffer { 35 public: 36 // The provided |client| must not be null, and |enable_resampling| determines 37 // resampling behavior (see |resample_|). 38 MotionEventBuffer(MotionEventBufferClient* client, bool enable_resampling); 39 ~MotionEventBuffer(); 40 41 // Should be called upon receipt of an event from the platform, prior to event 42 // dispatch to UI or content components. Events that can be coalesced will 43 // remain buffered until the next |Flush()|, while other events will be 44 // forwarded immediately (incidentally flushing currently buffered events). 45 void OnMotionEvent(const MotionEvent& event); 46 47 // Forward any buffered events, resampling if necessary (see |resample_|) 48 // according to the provided |frame_time|. This should be called in response 49 // to |SetNeedsFlush()| calls on the client. If the buffer is empty, no 50 // events will be forwarded, and if another flush is necessary it will be 51 // requested. 52 void Flush(base::TimeTicks frame_time); 53 54 private: 55 typedef ScopedVector<MotionEvent> MotionEventVector; 56 57 void FlushWithoutResampling(MotionEventVector events); 58 59 MotionEventBufferClient* const client_; 60 MotionEventVector buffered_events_; 61 62 // Time of the most recently extrapolated event. This will be 0 if the 63 // last sent event was not extrapolated. Used internally to guard against 64 // conflicts between events received from the platfrom that may have an 65 // earlier timestamp than that synthesized at the latest resample. 66 base::TimeTicks last_extrapolated_event_time_; 67 68 // Whether buffered events should be resampled upon |Flush()|. If true, short 69 // horizon interpolation/extrapolation will be used to synthesize the 70 // forwarded event. Otherwise the most recently buffered event will be 71 // forwarded, with preceding events as historical entries. Defaults to true. 72 bool resample_; 73 74 DISALLOW_COPY_AND_ASSIGN(MotionEventBuffer); 75 }; 76 77 } // namespace ui 78 79 #endif // UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_BUFFER_H_ 80
