motion_event_buffer.cc revision 5f1c94371a64b3196d4be9466099bb892df9b88e 
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#include "ui/events/gesture_detection/motion_event_buffer.h"
6
7#include "base/debug/trace_event.h"
8#include "ui/events/gesture_detection/motion_event.h"
9#include "ui/events/gesture_detection/motion_event_generic.h"
10
11namespace ui {
12namespace {
13
14// Latency added during resampling. A few milliseconds doesn't hurt much but
15// reduces the impact of mispredicted touch positions.
16const int kResampleLatencyMs = 5;
17
18// Minimum time difference between consecutive samples before attempting to
19// resample.
20const int kResampleMinDeltaMs = 2;
21
22// Maximum time to predict forward from the last known state, to avoid
23// predicting too far into the future.  This time is further bounded by 50% of
24// the last time delta.
25const int kResampleMaxPredictionMs = 8;
26
27typedef ScopedVector<MotionEvent> MotionEventVector;
28
29float Lerp(float a, float b, float alpha) {
30  return a + alpha * (b - a);
31}
32
33bool CanAddSample(const MotionEvent& event0, const MotionEvent& event1) {
34  DCHECK_EQ(event0.GetAction(), MotionEvent::ACTION_MOVE);
35  if (event1.GetAction() != MotionEvent::ACTION_MOVE)
36    return false;
37
38  const size_t pointer_count = event0.GetPointerCount();
39  if (pointer_count != event1.GetPointerCount())
40    return false;
41
42  for (size_t event0_i = 0; event0_i < pointer_count; ++event0_i) {
43    const int id = event0.GetPointerId(event0_i);
44    const int event1_i = event1.FindPointerIndexOfId(id);
45    if (event1_i == -1)
46      return false;
47    if (event0.GetToolType(event0_i) != event1.GetToolType(event1_i))
48      return false;
49  }
50
51  return true;
52}
53
54bool ShouldResampleTool(MotionEvent::ToolType tool) {
55  return tool == MotionEvent::TOOL_TYPE_UNKNOWN ||
56         tool == MotionEvent::TOOL_TYPE_FINGER;
57}
58
59size_t CountSamplesNoLaterThan(const MotionEventVector& batch,
60                               base::TimeTicks time) {
61  size_t count = 0;
62  while (count < batch.size() && batch[count]->GetEventTime() <= time)
63    ++count;
64  return count;
65}
66
67MotionEventVector ConsumeSamplesNoLaterThan(MotionEventVector* batch,
68                                            base::TimeTicks time) {
69  DCHECK(batch);
70  size_t count = CountSamplesNoLaterThan(*batch, time);
71  DCHECK_GE(batch->size(), count);
72  if (count == 0)
73    return MotionEventVector();
74
75  if (count == batch->size())
76    return batch->Pass();
77
78  // TODO(jdduke): Use a ScopedDeque to work around this mess.
79  MotionEventVector unconsumed_batch;
80  unconsumed_batch.insert(
81      unconsumed_batch.begin(), batch->begin() + count, batch->end());
82  batch->weak_erase(batch->begin() + count, batch->end());
83
84  unconsumed_batch.swap(*batch);
85  DCHECK_GE(unconsumed_batch.size(), 1U);
86  return unconsumed_batch.Pass();
87}
88
89PointerProperties PointerFromMotionEvent(const MotionEvent& event,
90                                         size_t pointer_index) {
91  PointerProperties result;
92  result.id = event.GetPointerId(pointer_index);
93  result.tool_type = event.GetToolType(pointer_index);
94  result.x = event.GetX(pointer_index);
95  result.y = event.GetY(pointer_index);
96  result.raw_x = event.GetRawX(pointer_index);
97  result.raw_y = event.GetRawY(pointer_index);
98  result.pressure = event.GetPressure(pointer_index);
99  result.touch_major = event.GetTouchMajor(pointer_index);
100  return result;
101}
102
103PointerProperties ResamplePointer(const MotionEvent& event0,
104                                  const MotionEvent& event1,
105                                  size_t event0_pointer_index,
106                                  size_t event1_pointer_index,
107                                  float alpha) {
108  DCHECK_EQ(event0.GetPointerId(event0_pointer_index),
109            event1.GetPointerId(event1_pointer_index));
110  // If the tool should not be resampled, use the latest event in the valid
111  // horizon (i.e., the event no later than the time interpolated by alpha).
112  if (!ShouldResampleTool(event0.GetToolType(event0_pointer_index))) {
113    if (alpha > 1)
114      return PointerFromMotionEvent(event1, event1_pointer_index);
115    else
116      return PointerFromMotionEvent(event0, event0_pointer_index);
117  }
118
119  PointerProperties p(PointerFromMotionEvent(event0, event0_pointer_index));
120  p.x = Lerp(p.x, event1.GetX(event1_pointer_index), alpha);
121  p.y = Lerp(p.y, event1.GetY(event1_pointer_index), alpha);
122  p.raw_x = Lerp(p.raw_x, event1.GetRawX(event1_pointer_index), alpha);
123  p.raw_y = Lerp(p.raw_y, event1.GetRawY(event1_pointer_index), alpha);
124  return p;
125}
126
127scoped_ptr<MotionEvent> ResampleMotionEvent(const MotionEvent& event0,
128                                            const MotionEvent& event1,
129                                            base::TimeTicks resample_time) {
130  DCHECK_EQ(MotionEvent::ACTION_MOVE, event0.GetAction());
131  DCHECK_EQ(event0.GetPointerCount(), event1.GetPointerCount());
132
133  const base::TimeTicks time0 = event0.GetEventTime();
134  const base::TimeTicks time1 = event1.GetEventTime();
135  DCHECK(time0 < time1);
136  DCHECK(time0 <= resample_time);
137
138  const float alpha = (resample_time - time0).InMillisecondsF() /
139                      (time1 - time0).InMillisecondsF();
140
141  scoped_ptr<MotionEventGeneric> event;
142  const size_t pointer_count = event0.GetPointerCount();
143  DCHECK_EQ(pointer_count, event1.GetPointerCount());
144  for (size_t event0_i = 0; event0_i < pointer_count; ++event0_i) {
145    int event1_i = event1.FindPointerIndexOfId(event0.GetPointerId(event0_i));
146    DCHECK_NE(event1_i, -1);
147    PointerProperties pointer = ResamplePointer(
148        event0, event1, event0_i, static_cast<size_t>(event1_i), alpha);
149
150    if (event0_i == 0) {
151      event.reset(new MotionEventGeneric(
152          MotionEvent::ACTION_MOVE, resample_time, pointer));
153    } else {
154      event->PushPointer(pointer);
155    }
156  }
157
158  DCHECK(event);
159  event->set_id(event0.GetId());
160  event->set_action_index(event0.GetActionIndex());
161  event->set_button_state(event0.GetButtonState());
162
163  return event.PassAs<MotionEvent>();
164}
165
166// MotionEvent implementation for storing multiple events, with the most
167// recent event used as the base event, and prior events used as the history.
168class CompoundMotionEvent : public ui::MotionEvent {
169 public:
170  explicit CompoundMotionEvent(MotionEventVector events)
171      : events_(events.Pass()) {
172    DCHECK_GE(events_.size(), 1U);
173  }
174  virtual ~CompoundMotionEvent() {}
175
176  virtual int GetId() const OVERRIDE { return latest().GetId(); }
177  virtual Action GetAction() const OVERRIDE { return latest().GetAction(); }
178  virtual int GetActionIndex() const OVERRIDE {
179    return latest().GetActionIndex();
180  }
181  virtual size_t GetPointerCount() const OVERRIDE {
182    return latest().GetPointerCount();
183  }
184  virtual int GetPointerId(size_t pointer_index) const OVERRIDE {
185    return latest().GetPointerId(pointer_index);
186  }
187  virtual float GetX(size_t pointer_index) const OVERRIDE {
188    return latest().GetX(pointer_index);
189  }
190  virtual float GetY(size_t pointer_index) const OVERRIDE {
191    return latest().GetY(pointer_index);
192  }
193  virtual float GetRawX(size_t pointer_index) const OVERRIDE {
194    return latest().GetRawX(pointer_index);
195  }
196  virtual float GetRawY(size_t pointer_index) const OVERRIDE {
197    return latest().GetRawY(pointer_index);
198  }
199  virtual float GetTouchMajor(size_t pointer_index) const OVERRIDE {
200    return latest().GetTouchMajor(pointer_index);
201  }
202  virtual float GetPressure(size_t pointer_index) const OVERRIDE {
203    return latest().GetPressure(pointer_index);
204  }
205  virtual ToolType GetToolType(size_t pointer_index) const OVERRIDE {
206    return latest().GetToolType(pointer_index);
207  }
208  virtual int GetButtonState() const OVERRIDE {
209    return latest().GetButtonState();
210  }
211  virtual base::TimeTicks GetEventTime() const OVERRIDE {
212    return latest().GetEventTime();
213  }
214  virtual size_t GetHistorySize() const OVERRIDE { return events_.size() - 1; }
215  virtual base::TimeTicks GetHistoricalEventTime(
216      size_t historical_index) const OVERRIDE {
217    DCHECK_LT(historical_index, GetHistorySize());
218    return events_[historical_index]->GetEventTime();
219  }
220  virtual float GetHistoricalTouchMajor(
221      size_t pointer_index,
222      size_t historical_index) const OVERRIDE {
223    DCHECK_LT(historical_index, GetHistorySize());
224    return events_[historical_index]->GetTouchMajor();
225  }
226  virtual float GetHistoricalX(size_t pointer_index,
227                               size_t historical_index) const OVERRIDE {
228    DCHECK_LT(historical_index, GetHistorySize());
229    return events_[historical_index]->GetX(pointer_index);
230  }
231  virtual float GetHistoricalY(size_t pointer_index,
232                               size_t historical_index) const OVERRIDE {
233    DCHECK_LT(historical_index, GetHistorySize());
234    return events_[historical_index]->GetY(pointer_index);
235  }
236  virtual scoped_ptr<MotionEvent> Clone() const OVERRIDE {
237    MotionEventVector cloned_events;
238    cloned_events.reserve(events_.size());
239    for (size_t i = 0; i < events_.size(); ++i)
240      cloned_events.push_back(events_[i]->Clone().release());
241    return scoped_ptr<MotionEvent>(
242        new CompoundMotionEvent(cloned_events.Pass()));
243  }
244  virtual scoped_ptr<MotionEvent> Cancel() const OVERRIDE {
245    return latest().Cancel();
246  }
247
248  // Returns the new, resampled event, or NULL if none was created.
249  // TODO(jdduke): Revisit resampling to handle cases where alternating frames
250  // are resampled or resampling is otherwise inconsistent, e.g., a 90hz input
251  // and 60hz frame signal could phase-align such that even frames yield an
252  // extrapolated event and odd frames are not resampled, crbug.com/399381.
253  const MotionEvent* TryResample(base::TimeTicks resample_time,
254                                 const ui::MotionEvent* next) {
255    DCHECK_EQ(GetAction(), ACTION_MOVE);
256    const ui::MotionEvent* event0 = NULL;
257    const ui::MotionEvent* event1 = NULL;
258    if (next) {
259      DCHECK(resample_time < next->GetEventTime());
260      // Interpolate between current sample and future sample.
261      event0 = events_.back();
262      event1 = next;
263    } else if (events_.size() >= 2) {
264      // Extrapolate future sample using current sample and past sample.
265      event0 = events_[events_.size() - 2];
266      event1 = events_[events_.size() - 1];
267
268      const base::TimeTicks time1 = event1->GetEventTime();
269      base::TimeTicks max_predict =
270          time1 +
271          std::min((event1->GetEventTime() - event0->GetEventTime()) / 2,
272                   base::TimeDelta::FromMilliseconds(kResampleMaxPredictionMs));
273      if (resample_time > max_predict) {
274        TRACE_EVENT_INSTANT2("input",
275                             "MotionEventBuffer::TryResample prediction adjust",
276                             TRACE_EVENT_SCOPE_THREAD,
277                             "original(ms)",
278                             (resample_time - time1).InMilliseconds(),
279                             "adjusted(ms)",
280                             (max_predict - time1).InMilliseconds());
281        resample_time = max_predict;
282      }
283    } else {
284      TRACE_EVENT_INSTANT0("input",
285                           "MotionEventBuffer::TryResample insufficient data",
286                           TRACE_EVENT_SCOPE_THREAD);
287      return NULL;
288    }
289
290    DCHECK(event0);
291    DCHECK(event1);
292    const base::TimeTicks time0 = event0->GetEventTime();
293    const base::TimeTicks time1 = event1->GetEventTime();
294    base::TimeDelta delta = time1 - time0;
295    if (delta < base::TimeDelta::FromMilliseconds(kResampleMinDeltaMs)) {
296      TRACE_EVENT_INSTANT1("input",
297                           "MotionEventBuffer::TryResample failure",
298                           TRACE_EVENT_SCOPE_THREAD,
299                           "event_delta_too_small(ms)",
300                           delta.InMilliseconds());
301      return NULL;
302    }
303
304    events_.push_back(
305        ResampleMotionEvent(*event0, *event1, resample_time).release());
306    return events_.back();
307  }
308
309  size_t samples() const { return events_.size(); }
310
311 private:
312  const MotionEvent& latest() const { return *events_.back(); }
313
314  // Events are in order from oldest to newest.
315  MotionEventVector events_;
316
317  DISALLOW_COPY_AND_ASSIGN(CompoundMotionEvent);
318};
319
320}  // namespace
321
322MotionEventBuffer::MotionEventBuffer(MotionEventBufferClient* client,
323                                     bool enable_resampling)
324    : client_(client), resample_(enable_resampling) {
325}
326
327MotionEventBuffer::~MotionEventBuffer() {
328}
329
330void MotionEventBuffer::OnMotionEvent(const MotionEvent& event) {
331  if (event.GetAction() != MotionEvent::ACTION_MOVE) {
332    last_extrapolated_event_time_ = base::TimeTicks();
333    if (!buffered_events_.empty())
334      FlushWithoutResampling(buffered_events_.Pass());
335    client_->ForwardMotionEvent(event);
336    return;
337  }
338
339  // Guard against events that are *older* than the last one that may have been
340  // artificially synthesized.
341  if (!last_extrapolated_event_time_.is_null()) {
342    DCHECK(buffered_events_.empty());
343    if (event.GetEventTime() < last_extrapolated_event_time_)
344      return;
345    last_extrapolated_event_time_ = base::TimeTicks();
346  }
347
348  scoped_ptr<MotionEvent> clone = event.Clone();
349  if (buffered_events_.empty()) {
350    buffered_events_.push_back(clone.release());
351    client_->SetNeedsFlush();
352    return;
353  }
354
355  if (CanAddSample(*buffered_events_.front(), *clone)) {
356    DCHECK(buffered_events_.back()->GetEventTime() <= clone->GetEventTime());
357  } else {
358    FlushWithoutResampling(buffered_events_.Pass());
359  }
360
361  buffered_events_.push_back(clone.release());
362  // No need to request another flush as the first event will have requested it.
363}
364
365void MotionEventBuffer::Flush(base::TimeTicks frame_time) {
366  if (buffered_events_.empty())
367    return;
368
369  // Shifting the sample time back slightly minimizes the potential for
370  // misprediction when extrapolating events.
371  if (resample_)
372    frame_time -= base::TimeDelta::FromMilliseconds(kResampleLatencyMs);
373
374  // TODO(jdduke): Use a persistent MotionEventVector vector for temporary
375  // storage.
376  MotionEventVector events(
377      ConsumeSamplesNoLaterThan(&buffered_events_, frame_time));
378  if (events.empty()) {
379    DCHECK(!buffered_events_.empty());
380    client_->SetNeedsFlush();
381    return;
382  }
383
384  if (!resample_ || (events.size() == 1 && buffered_events_.empty())) {
385    FlushWithoutResampling(events.Pass());
386    if (!buffered_events_.empty())
387      client_->SetNeedsFlush();
388    return;
389  }
390
391  CompoundMotionEvent resampled_event(events.Pass());
392  base::TimeTicks original_event_time = resampled_event.GetEventTime();
393  const MotionEvent* next_event =
394      !buffered_events_.empty() ? buffered_events_.front() : NULL;
395
396  // Try to interpolate/extrapolate a new event at |frame_time|. Note that
397  // |new_event|, if non-NULL, is owned by |resampled_event_|.
398  const MotionEvent* new_event =
399      resampled_event.TryResample(frame_time, next_event);
400
401  // Log the extrapolated event time, guarding against subsequently queued
402  // events that might have an earlier timestamp.
403  if (!next_event && new_event &&
404      new_event->GetEventTime() > original_event_time) {
405    last_extrapolated_event_time_ = new_event->GetEventTime();
406  } else {
407    last_extrapolated_event_time_ = base::TimeTicks();
408  }
409
410  client_->ForwardMotionEvent(resampled_event);
411  if (!buffered_events_.empty())
412    client_->SetNeedsFlush();
413}
414
415void MotionEventBuffer::FlushWithoutResampling(MotionEventVector events) {
416  last_extrapolated_event_time_ = base::TimeTicks();
417  if (events.empty())
418    return;
419
420  if (events.size() == 1) {
421    // Avoid CompoundEvent creation to prevent unnecessary allocations.
422    scoped_ptr<MotionEvent> event(events.front());
423    events.weak_clear();
424    client_->ForwardMotionEvent(*event);
425    return;
426  }
427
428  CompoundMotionEvent compound_event(events.Pass());
429  client_->ForwardMotionEvent(compound_event);
430}
431
432}  // namespace ui
433