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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.
#include "ui/events/gesture_detection/motion_event_buffer.h"
#include <stddef.h>
#include <utility>
#include "base/trace_event/trace_event.h"
#include "ui/events/gesture_detection/motion_event_generic.h"
namespace ui {
namespace {
// Latency added during resampling. A few milliseconds doesn't hurt much but
// reduces the impact of mispredicted touch positions.
const int kResampleLatencyMs = 5;
// Minimum time difference between consecutive samples before attempting to
// resample.
const int kResampleMinDeltaMs = 2;
// Maximum time to predict forward from the last known state, to avoid
// predicting too far into the future. This time is further bounded by 50% of
// the last time delta.
const int kResampleMaxPredictionMs = 8;
typedef ScopedVector<MotionEventGeneric> MotionEventVector;
float Lerp(float a, float b, float alpha) {
return a + alpha * (b - a);
}
bool CanAddSample(const MotionEvent& event0, const MotionEvent& event1) {
DCHECK_EQ(event0.GetAction(), MotionEvent::ACTION_MOVE);
if (event1.GetAction() != MotionEvent::ACTION_MOVE)
return false;
const size_t pointer_count = event0.GetPointerCount();
if (pointer_count != event1.GetPointerCount())
return false;
for (size_t event0_i = 0; event0_i < pointer_count; ++event0_i) {
const int id = event0.GetPointerId(event0_i);
const int event1_i = event1.FindPointerIndexOfId(id);
if (event1_i == -1)
return false;
if (event0.GetToolType(event0_i) != event1.GetToolType(event1_i))
return false;
}
return true;
}
bool ShouldResampleTool(MotionEvent::ToolType tool) {
return tool == MotionEvent::TOOL_TYPE_UNKNOWN ||
tool == MotionEvent::TOOL_TYPE_FINGER;
}
size_t CountSamplesNoLaterThan(const MotionEventVector& batch,
base::TimeTicks time) {
size_t count = 0;
while (count < batch.size() && batch[count]->GetEventTime() <= time)
++count;
return count;
}
MotionEventVector ConsumeSamplesNoLaterThan(MotionEventVector* batch,
base::TimeTicks time) {
DCHECK(batch);
size_t count = CountSamplesNoLaterThan(*batch, time);
DCHECK_GE(batch->size(), count);
if (count == 0)
return MotionEventVector();
if (count == batch->size())
return std::move(*batch);
// TODO(jdduke): Use a ScopedDeque to work around this mess.
MotionEventVector unconsumed_batch;
unconsumed_batch.insert(
unconsumed_batch.begin(), batch->begin() + count, batch->end());
batch->weak_erase(batch->begin() + count, batch->end());
unconsumed_batch.swap(*batch);
DCHECK_GE(unconsumed_batch.size(), 1U);
return unconsumed_batch;
}
// Linearly interpolate the pointer position between two MotionEvent samples.
// Only pointers of finger or unknown type will be resampled.
PointerProperties ResamplePointer(const MotionEvent& event0,
const MotionEvent& event1,
size_t event0_pointer_index,
size_t event1_pointer_index,
float alpha) {
DCHECK_EQ(event0.GetPointerId(event0_pointer_index),
event1.GetPointerId(event1_pointer_index));
// If the tool should not be resampled, use the latest event in the valid
// horizon (i.e., the event no later than the time interpolated by alpha).
if (!ShouldResampleTool(event0.GetToolType(event0_pointer_index))) {
if (alpha > 1)
return PointerProperties(event1, event1_pointer_index);
else
return PointerProperties(event0, event0_pointer_index);
}
PointerProperties p(event0, event0_pointer_index);
p.x = Lerp(p.x, event1.GetX(event1_pointer_index), alpha);
p.y = Lerp(p.y, event1.GetY(event1_pointer_index), alpha);
p.raw_x = Lerp(p.raw_x, event1.GetRawX(event1_pointer_index), alpha);
p.raw_y = Lerp(p.raw_y, event1.GetRawY(event1_pointer_index), alpha);
return p;
}
// Linearly interpolate the pointers between two event samples using the
// provided |resample_time|.
std::unique_ptr<MotionEventGeneric> ResampleMotionEvent(
const MotionEvent& event0,
const MotionEvent& event1,
base::TimeTicks resample_time) {
DCHECK_EQ(MotionEvent::ACTION_MOVE, event0.GetAction());
DCHECK_EQ(event0.GetPointerCount(), event1.GetPointerCount());
const base::TimeTicks time0 = event0.GetEventTime();
const base::TimeTicks time1 = event1.GetEventTime();
DCHECK(time0 < time1);
DCHECK(time0 <= resample_time);
const float alpha = (resample_time - time0).InMillisecondsF() /
(time1 - time0).InMillisecondsF();
std::unique_ptr<MotionEventGeneric> event;
const size_t pointer_count = event0.GetPointerCount();
DCHECK_EQ(pointer_count, event1.GetPointerCount());
for (size_t event0_i = 0; event0_i < pointer_count; ++event0_i) {
int event1_i = event1.FindPointerIndexOfId(event0.GetPointerId(event0_i));
DCHECK_NE(event1_i, -1);
PointerProperties pointer = ResamplePointer(
event0, event1, event0_i, static_cast<size_t>(event1_i), alpha);
if (event0_i == 0) {
event.reset(new MotionEventGeneric(
MotionEvent::ACTION_MOVE, resample_time, pointer));
} else {
event->PushPointer(pointer);
}
}
DCHECK(event);
event->set_button_state(event0.GetButtonState());
return event;
}
// Synthesize a compound MotionEventGeneric event from a sequence of events.
// Events must be in non-decreasing (time) order.
std::unique_ptr<MotionEventGeneric> ConsumeSamples(MotionEventVector events) {
DCHECK(!events.empty());
std::unique_ptr<MotionEventGeneric> event(events.back());
for (size_t i = 0; i + 1 < events.size(); ++i)
event->PushHistoricalEvent(std::unique_ptr<MotionEvent>(events[i]));
events.weak_clear();
return event;
}
// Consume a series of event samples, attempting to synthesize a new, synthetic
// event if the samples and sample time meet certain interpolation/extrapolation
// conditions. If such conditions are met, the provided samples will be added
// to the synthetic event's history, otherwise, the samples will be used to
// generate a basic, compound event.
// TODO(jdduke): Revisit resampling to handle cases where alternating frames
// are resampled or resampling is otherwise inconsistent, e.g., a 90hz input
// and 60hz frame signal could phase-align such that even frames yield an
// extrapolated event and odd frames are not resampled, crbug.com/399381.
std::unique_ptr<MotionEventGeneric> ConsumeSamplesAndTryResampling(
base::TimeTicks resample_time,
MotionEventVector events,
const MotionEvent* next) {
const ui::MotionEvent* event0 = nullptr;
const ui::MotionEvent* event1 = nullptr;
if (next) {
DCHECK(resample_time < next->GetEventTime());
// Interpolate between current sample and future sample.
event0 = events.back();
event1 = next;
} else if (events.size() >= 2) {
// Extrapolate future sample using current sample and past sample.
event0 = events[events.size() - 2];
event1 = events[events.size() - 1];
const base::TimeTicks time1 = event1->GetEventTime();
base::TimeTicks max_predict =
time1 +
std::min((event1->GetEventTime() - event0->GetEventTime()) / 2,
base::TimeDelta::FromMilliseconds(kResampleMaxPredictionMs));
if (resample_time > max_predict) {
TRACE_EVENT_INSTANT2("input",
"MotionEventBuffer::TryResample prediction adjust",
TRACE_EVENT_SCOPE_THREAD,
"original(ms)",
(resample_time - time1).InMilliseconds(),
"adjusted(ms)",
(max_predict - time1).InMilliseconds());
resample_time = max_predict;
}
} else {
TRACE_EVENT_INSTANT0("input",
"MotionEventBuffer::TryResample insufficient data",
TRACE_EVENT_SCOPE_THREAD);
return ConsumeSamples(std::move(events));
}
DCHECK(event0);
DCHECK(event1);
const base::TimeTicks time0 = event0->GetEventTime();
const base::TimeTicks time1 = event1->GetEventTime();
base::TimeDelta delta = time1 - time0;
if (delta < base::TimeDelta::FromMilliseconds(kResampleMinDeltaMs)) {
TRACE_EVENT_INSTANT1("input",
"MotionEventBuffer::TryResample failure",
TRACE_EVENT_SCOPE_THREAD,
"event_delta_too_small(ms)",
delta.InMilliseconds());
return ConsumeSamples(std::move(events));
}
std::unique_ptr<MotionEventGeneric> resampled_event =
ResampleMotionEvent(*event0, *event1, resample_time);
for (size_t i = 0; i < events.size(); ++i)
resampled_event->PushHistoricalEvent(
std::unique_ptr<MotionEvent>(events[i]));
events.weak_clear();
return resampled_event;
}
} // namespace
MotionEventBuffer::MotionEventBuffer(MotionEventBufferClient* client,
bool enable_resampling)
: client_(client), resample_(enable_resampling) {
}
MotionEventBuffer::~MotionEventBuffer() {
}
void MotionEventBuffer::OnMotionEvent(const MotionEvent& event) {
DCHECK_EQ(0U, event.GetHistorySize());
if (event.GetAction() != MotionEvent::ACTION_MOVE) {
last_extrapolated_event_time_ = base::TimeTicks();
if (!buffered_events_.empty())
FlushWithoutResampling(std::move(buffered_events_));
client_->ForwardMotionEvent(event);
return;
}
// Guard against events that are *older* than the last one that may have been
// artificially synthesized.
if (!last_extrapolated_event_time_.is_null()) {
DCHECK(buffered_events_.empty());
if (event.GetEventTime() < last_extrapolated_event_time_)
return;
last_extrapolated_event_time_ = base::TimeTicks();
}
std::unique_ptr<MotionEventGeneric> clone =
MotionEventGeneric::CloneEvent(event);
if (buffered_events_.empty()) {
buffered_events_.push_back(std::move(clone));
client_->SetNeedsFlush();
return;
}
if (CanAddSample(*buffered_events_.front(), *clone)) {
DCHECK(buffered_events_.back()->GetEventTime() <= clone->GetEventTime());
} else {
FlushWithoutResampling(std::move(buffered_events_));
}
buffered_events_.push_back(std::move(clone));
// No need to request another flush as the first event will have requested it.
}
void MotionEventBuffer::Flush(base::TimeTicks frame_time) {
if (buffered_events_.empty())
return;
// Shifting the sample time back slightly minimizes the potential for
// misprediction when extrapolating events.
if (resample_)
frame_time -= base::TimeDelta::FromMilliseconds(kResampleLatencyMs);
// TODO(jdduke): Use a persistent MotionEventVector vector for temporary
// storage.
MotionEventVector events(
ConsumeSamplesNoLaterThan(&buffered_events_, frame_time));
if (events.empty()) {
DCHECK(!buffered_events_.empty());
client_->SetNeedsFlush();
return;
}
if (!resample_ || (events.size() == 1 && buffered_events_.empty())) {
FlushWithoutResampling(std::move(events));
if (!buffered_events_.empty())
client_->SetNeedsFlush();
return;
}
FlushWithResampling(std::move(events), frame_time);
}
void MotionEventBuffer::FlushWithResampling(MotionEventVector events,
base::TimeTicks resample_time) {
DCHECK(!events.empty());
base::TimeTicks original_event_time = events.back()->GetEventTime();
const MotionEvent* next_event =
!buffered_events_.empty() ? buffered_events_.front() : nullptr;
std::unique_ptr<MotionEventGeneric> resampled_event =
ConsumeSamplesAndTryResampling(resample_time, std::move(events),
next_event);
DCHECK(resampled_event);
// Log the extrapolated event time, guarding against subsequently queued
// events that might have an earlier timestamp.
if (!next_event && resampled_event->GetEventTime() > original_event_time) {
last_extrapolated_event_time_ = resampled_event->GetEventTime();
} else {
last_extrapolated_event_time_ = base::TimeTicks();
}
client_->ForwardMotionEvent(*resampled_event);
if (!buffered_events_.empty())
client_->SetNeedsFlush();
}
void MotionEventBuffer::FlushWithoutResampling(MotionEventVector events) {
last_extrapolated_event_time_ = base::TimeTicks();
if (events.empty())
return;
client_->ForwardMotionEvent(*ConsumeSamples(std::move(events)));
}
} // namespace ui