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/**
* Copyright 2024 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#define LOG_TAG "LegacyResampler"
#include <algorithm>
#include <chrono>
#include <android-base/logging.h>
#include <android-base/properties.h>
#include <input/Resampler.h>
#include <utils/Timers.h>
using std::chrono::nanoseconds;
namespace android {
namespace {
const bool IS_DEBUGGABLE_BUILD =
#if defined(__ANDROID__)
android::base::GetBoolProperty("ro.debuggable", false);
#else
true;
#endif
bool debugResampling() {
if (!IS_DEBUGGABLE_BUILD) {
static const bool DEBUG_TRANSPORT_RESAMPLING =
__android_log_is_loggable(ANDROID_LOG_DEBUG, LOG_TAG "Resampling",
ANDROID_LOG_INFO);
return DEBUG_TRANSPORT_RESAMPLING;
}
return __android_log_is_loggable(ANDROID_LOG_DEBUG, LOG_TAG "Resampling", ANDROID_LOG_INFO);
}
constexpr std::chrono::milliseconds RESAMPLE_LATENCY{5};
constexpr std::chrono::milliseconds RESAMPLE_MIN_DELTA{2};
constexpr std::chrono::milliseconds RESAMPLE_MAX_DELTA{20};
constexpr std::chrono::milliseconds RESAMPLE_MAX_PREDICTION{8};
inline float lerp(float a, float b, float alpha) {
return a + alpha * (b - a);
}
const PointerCoords calculateResampledCoords(const PointerCoords& a, const PointerCoords& b,
const float alpha) {
// Ensure the struct PointerCoords is initialized.
PointerCoords resampledCoords{};
resampledCoords.isResampled = true;
resampledCoords.setAxisValue(AMOTION_EVENT_AXIS_X, lerp(a.getX(), b.getX(), alpha));
resampledCoords.setAxisValue(AMOTION_EVENT_AXIS_Y, lerp(a.getY(), b.getY(), alpha));
return resampledCoords;
}
} // namespace
void LegacyResampler::updateLatestSamples(const MotionEvent& motionEvent) {
const size_t motionEventSampleSize = motionEvent.getHistorySize() + 1;
for (size_t i = 0; i < motionEventSampleSize; ++i) {
Sample sample{static_cast<nanoseconds>(motionEvent.getHistoricalEventTime(i)),
*motionEvent.getPointerProperties(0),
motionEvent.getSamplePointerCoords()[i]};
mLatestSamples.pushBack(sample);
}
}
void LegacyResampler::interpolate(const nanoseconds resampleTime, MotionEvent& motionEvent,
const InputMessage& futureSample) const {
const Sample pastSample = mLatestSamples.back();
const nanoseconds delta =
static_cast<nanoseconds>(futureSample.body.motion.eventTime) - pastSample.eventTime;
if (delta < RESAMPLE_MIN_DELTA) {
LOG_IF(INFO, debugResampling()) << "Not resampled. Delta is too small: " << delta << "ns.";
return;
}
const float alpha =
std::chrono::duration<float, std::milli>(resampleTime - pastSample.eventTime) / delta;
const PointerCoords resampledCoords =
calculateResampledCoords(pastSample.pointer.coords,
futureSample.body.motion.pointers[0].coords, alpha);
motionEvent.addSample(resampleTime.count(), &resampledCoords, motionEvent.getId());
}
void LegacyResampler::extrapolate(const nanoseconds resampleTime, MotionEvent& motionEvent) const {
if (mLatestSamples.size() < 2) {
return;
}
const Sample pastSample = *(mLatestSamples.end() - 2);
const Sample presentSample = *(mLatestSamples.end() - 1);
const nanoseconds delta =
static_cast<nanoseconds>(presentSample.eventTime - pastSample.eventTime);
if (delta < RESAMPLE_MIN_DELTA) {
LOG_IF(INFO, debugResampling()) << "Not resampled. Delta is too small: " << delta << "ns.";
return;
} else if (delta > RESAMPLE_MAX_DELTA) {
LOG_IF(INFO, debugResampling()) << "Not resampled. Delta is too large: " << delta << "ns.";
return;
}
// The farthest future time to which we can extrapolate. If the given resampleTime exceeds this,
// we use this value as the resample time target.
const nanoseconds farthestPrediction = static_cast<nanoseconds>(presentSample.eventTime) +
std::min<nanoseconds>(delta / 2, RESAMPLE_MAX_PREDICTION);
const nanoseconds newResampleTime =
(resampleTime > farthestPrediction) ? (farthestPrediction) : (resampleTime);
LOG_IF(INFO, debugResampling() && newResampleTime == farthestPrediction)
<< "Resample time is too far in the future. Adjusting prediction from "
<< (resampleTime - presentSample.eventTime) << " to "
<< (farthestPrediction - presentSample.eventTime) << "ns.";
const float alpha =
std::chrono::duration<float, std::milli>(newResampleTime - pastSample.eventTime) /
delta;
const PointerCoords resampledCoords =
calculateResampledCoords(pastSample.pointer.coords, presentSample.pointer.coords,
alpha);
motionEvent.addSample(newResampleTime.count(), &resampledCoords, motionEvent.getId());
}
void LegacyResampler::resampleMotionEvent(const nanoseconds resampleTime, MotionEvent& motionEvent,
const InputMessage* futureSample) {
if (mPreviousDeviceId && *mPreviousDeviceId != motionEvent.getDeviceId()) {
mLatestSamples.clear();
}
mPreviousDeviceId = motionEvent.getDeviceId();
updateLatestSamples(motionEvent);
if (futureSample) {
interpolate(resampleTime, motionEvent, *futureSample);
} else {
extrapolate(resampleTime, motionEvent);
}
LOG_IF(INFO, debugResampling()) << "Not resampled. Not enough data.";
}
} // namespace android
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