Refactor resampler logic to constrain MotionEvent mutation
Refactored resampler logic to constrain the functions where MotionEvent
can mutate.
Bug: 297226446
Flag: EXEMPT refactor
Test: TEST=libinput_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST --gtest_filter="ResamplerTest*"
Change-Id: I4b9c9140b73cd45f866dc51931b03cdf2883e5a3
diff --git a/include/input/Resampler.h b/include/input/Resampler.h
index ff9c4b0..5980d5d 100644
--- a/include/input/Resampler.h
+++ b/include/input/Resampler.h
@@ -44,7 +44,7 @@
* samples by the end of the resampling. No other field of motionEvent should be modified.
* - If resampling does not occur, then motionEvent must not be modified in any way.
*/
- virtual void resampleMotionEvent(const std::chrono::nanoseconds resampleTime,
+ virtual void resampleMotionEvent(std::chrono::nanoseconds resampleTime,
MotionEvent& motionEvent,
const InputMessage* futureSample) = 0;
};
@@ -60,7 +60,7 @@
* data, LegacyResampler will extrapolate. Otherwise, no resampling takes place and
* `motionEvent` is unmodified.
*/
- void resampleMotionEvent(const std::chrono::nanoseconds resampleTime, MotionEvent& motionEvent,
+ void resampleMotionEvent(std::chrono::nanoseconds resampleTime, MotionEvent& motionEvent,
const InputMessage* futureSample) override;
private:
@@ -72,10 +72,6 @@
struct Sample {
std::chrono::nanoseconds eventTime;
Pointer pointer;
-
- Sample(const std::chrono::nanoseconds eventTime, const PointerProperties& properties,
- const PointerCoords& coords)
- : eventTime{eventTime}, pointer{properties, coords} {}
};
/**
@@ -99,17 +95,34 @@
void updateLatestSamples(const MotionEvent& motionEvent);
/**
- * May add a sample at the end of motionEvent with eventTime equal to resampleTime, and
- * interpolated coordinates between the latest motionEvent sample and futureSample.
+ * Checks if there are necessary conditions to interpolate. For example, interpolation cannot
+ * take place if samples are too far apart in time. mLatestSamples must have at least one sample
+ * when canInterpolate is invoked.
*/
- void interpolate(const std::chrono::nanoseconds resampleTime, MotionEvent& motionEvent,
- const InputMessage& futureSample) const;
+ bool canInterpolate(const InputMessage& futureSample) const;
/**
- * May add a sample at the end of motionEvent by extrapolating from the latest two samples. The
- * added sample either has eventTime equal to resampleTime, or an earlier time if resampleTime
- * is too far in the future.
+ * Returns a sample interpolated between the latest sample of mLatestSamples and futureSample,
+ * if the conditions from canInterpolate are satisfied. Otherwise, returns nullopt.
+ * mLatestSamples must have at least one sample when attemptInterpolation is called.
*/
- void extrapolate(const std::chrono::nanoseconds resampleTime, MotionEvent& motionEvent) const;
+ std::optional<Sample> attemptInterpolation(std::chrono::nanoseconds resampleTime,
+ const InputMessage& futureSample) const;
+
+ /**
+ * Checks if there are necessary conditions to extrapolate. That is, there are at least two
+ * samples in mLatestSamples, and delta is bounded within a time interval.
+ */
+ bool canExtrapolate() const;
+
+ /**
+ * Returns a sample extrapolated from the two samples of mLatestSamples, if the conditions from
+ * canExtrapolate are satisfied. The returned sample either has eventTime equal to resampleTime,
+ * or an earlier time if resampleTime is too far in the future. If canExtrapolate returns false,
+ * this function returns nullopt.
+ */
+ std::optional<Sample> attemptExtrapolation(std::chrono::nanoseconds resampleTime) const;
+
+ inline static void addSampleToMotionEvent(const Sample& sample, MotionEvent& motionEvent);
};
} // namespace android
\ No newline at end of file
diff --git a/libs/input/Resampler.cpp b/libs/input/Resampler.cpp
index 836a97a..342f7f5 100644
--- a/libs/input/Resampler.cpp
+++ b/libs/input/Resampler.cpp
@@ -60,8 +60,8 @@
return a + alpha * (b - a);
}
-const PointerCoords calculateResampledCoords(const PointerCoords& a, const PointerCoords& b,
- const float alpha) {
+PointerCoords calculateResampledCoords(const PointerCoords& a, const PointerCoords& b,
+ float alpha) {
// We use the value of alpha to initialize resampledCoords with the latest sample information.
PointerCoords resampledCoords = (alpha < 1.0f) ? a : b;
resampledCoords.isResampled = true;
@@ -72,52 +72,85 @@
} // 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);
+ const size_t numSamples = motionEvent.getHistorySize() + 1;
+ for (size_t i = 0; i < numSamples; ++i) {
+ mLatestSamples.pushBack(
+ Sample{static_cast<nanoseconds>(motionEvent.getHistoricalEventTime(i)),
+ Pointer{*motionEvent.getPointerProperties(0),
+ motionEvent.getSamplePointerCoords()[i]}});
}
}
-void LegacyResampler::interpolate(const nanoseconds resampleTime, MotionEvent& motionEvent,
- const InputMessage& futureSample) const {
- const Sample pastSample = mLatestSamples.back();
+bool LegacyResampler::canInterpolate(const InputMessage& futureSample) const {
+ LOG_IF(FATAL, mLatestSamples.empty())
+ << "Not resampled. mLatestSamples must not be empty to interpolate.";
+
+ const Sample& pastSample = *(mLatestSamples.end() - 1);
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;
+ return false;
}
+ return true;
+}
+
+std::optional<LegacyResampler::Sample> LegacyResampler::attemptInterpolation(
+ nanoseconds resampleTime, const InputMessage& futureSample) const {
+ if (!canInterpolate(futureSample)) {
+ return std::nullopt;
+ }
+ LOG_IF(FATAL, mLatestSamples.empty())
+ << "Not resampled. mLatestSamples must not be empty to interpolate.";
+
+ const Sample& pastSample = *(mLatestSamples.end() - 1);
+ const nanoseconds delta =
+ static_cast<nanoseconds>(futureSample.body.motion.eventTime) - pastSample.eventTime;
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());
+
+ return Sample{resampleTime, Pointer{pastSample.pointer.properties, resampledCoords}};
}
-void LegacyResampler::extrapolate(const nanoseconds resampleTime, MotionEvent& motionEvent) const {
+bool LegacyResampler::canExtrapolate() const {
if (mLatestSamples.size() < 2) {
- return;
+ LOG_IF(INFO, debugResampling()) << "Not resampled. Not enough data.";
+ return false;
}
- const Sample pastSample = *(mLatestSamples.end() - 2);
- const Sample presentSample = *(mLatestSamples.end() - 1);
- const nanoseconds delta =
- static_cast<nanoseconds>(presentSample.eventTime - pastSample.eventTime);
+
+ const Sample& pastSample = *(mLatestSamples.end() - 2);
+ const Sample& presentSample = *(mLatestSamples.end() - 1);
+
+ const nanoseconds delta = presentSample.eventTime - pastSample.eventTime;
if (delta < RESAMPLE_MIN_DELTA) {
LOG_IF(INFO, debugResampling()) << "Not resampled. Delta is too small: " << delta << "ns.";
- return;
+ return false;
} else if (delta > RESAMPLE_MAX_DELTA) {
LOG_IF(INFO, debugResampling()) << "Not resampled. Delta is too large: " << delta << "ns.";
- return;
+ return false;
}
+ return true;
+}
+
+std::optional<LegacyResampler::Sample> LegacyResampler::attemptExtrapolation(
+ nanoseconds resampleTime) const {
+ if (!canExtrapolate()) {
+ return std::nullopt;
+ }
+ LOG_IF(FATAL, mLatestSamples.size() < 2)
+ << "Not resampled. mLatestSamples must have at least two samples to extrapolate.";
+
+ const Sample& pastSample = *(mLatestSamples.end() - 2);
+ const Sample& presentSample = *(mLatestSamples.end() - 1);
+
+ const nanoseconds delta = presentSample.eventTime - pastSample.eventTime;
// 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 farthestPrediction =
+ presentSample.eventTime + std::min<nanoseconds>(delta / 2, RESAMPLE_MAX_PREDICTION);
const nanoseconds newResampleTime =
(resampleTime > farthestPrediction) ? (farthestPrediction) : (resampleTime);
LOG_IF(INFO, debugResampling() && newResampleTime == farthestPrediction)
@@ -127,25 +160,32 @@
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());
+
+ return Sample{newResampleTime, Pointer{presentSample.pointer.properties, resampledCoords}};
}
-void LegacyResampler::resampleMotionEvent(const nanoseconds resampleTime, MotionEvent& motionEvent,
+inline void LegacyResampler::addSampleToMotionEvent(const Sample& sample,
+ MotionEvent& motionEvent) {
+ motionEvent.addSample(sample.eventTime.count(), &sample.pointer.coords, motionEvent.getId());
+}
+
+void LegacyResampler::resampleMotionEvent(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);
+
+ const std::optional<Sample> sample = (futureSample != nullptr)
+ ? (attemptInterpolation(resampleTime, *futureSample))
+ : (attemptExtrapolation(resampleTime));
+ if (sample.has_value()) {
+ addSampleToMotionEvent(*sample, motionEvent);
}
- LOG_IF(INFO, debugResampling()) << "Not resampled. Not enough data.";
}
} // namespace android