Merge "Reimplement Chromium's OneEuroFilter to InputConsumer" into main

Author: Treehugger Robot

include/input/CoordinateFilter.h

@@ -0,0 +1,54 @@
+/**
+ * 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.
+ */
+
+#pragma once
+
+#include <chrono>
+
+#include <input/Input.h>
+#include <input/OneEuroFilter.h>
+
+namespace android {
+
+/**
+ * Pair of OneEuroFilters that independently filter X and Y coordinates. Both filters share the same
+ * constructor's parameters. The minimum cutoff frequency is the base cutoff frequency, that is, the
+ * resulting cutoff frequency in the absence of signal's speed. Likewise, beta is a scaling factor
+ * of the signal's speed that sets how much the signal's speed contributes to the resulting cutoff
+ * frequency. The adaptive cutoff frequency criterion is f_c = f_c_min + β|̇x_filtered|
+ */
+class CoordinateFilter {
+public:
+    explicit CoordinateFilter(float minCutoffFreq, float beta);
+
+    /**
+     * Filters in place only the AXIS_X and AXIS_Y fields from coords. Each call to filter must
+     * provide a timestamp strictly greater than the timestamp of the previous call. The first time
+     * this method is invoked no filtering takes place. Subsequent calls do overwrite `coords` with
+     * filtered data.
+     *
+     * @param timestamp The timestamps at which to filter. It must be greater than the one passed in
+     * the previous call.
+     * @param coords Coordinates to be overwritten by the corresponding filtered coordinates.
+     */
+    void filter(std::chrono::duration<float> timestamp, PointerCoords& coords);
+
+private:
+    OneEuroFilter mXFilter;
+    OneEuroFilter mYFilter;
+};
+
+} // namespace android

include/input/OneEuroFilter.h

@@ -0,0 +1,101 @@
+/**
+ * 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.
+ */
+
+#pragma once
+
+#include <chrono>
+#include <optional>
+
+#include <input/Input.h>
+
+namespace android {
+
+/**
+ * Low pass filter with adaptive low pass frequency based on the signal's speed. The signal's cutoff
+ * frequency is determined by f_c = f_c_min + β|̇x_filtered|. Refer to
+ * https://dl.acm.org/doi/10.1145/2207676.2208639 for details on how the filter works and how to
+ * tune it.
+ */
+class OneEuroFilter {
+public:
+    /**
+     * Default cutoff frequency of the filtered signal's speed. 1.0 Hz is the value in the filter's
+     * paper.
+     */
+    static constexpr float kDefaultSpeedCutoffFreq = 1.0;
+
+    OneEuroFilter() = delete;
+
+    explicit OneEuroFilter(float minCutoffFreq, float beta,
+                           float speedCutoffFreq = kDefaultSpeedCutoffFreq);
+
+    OneEuroFilter(const OneEuroFilter&) = delete;
+    OneEuroFilter& operator=(const OneEuroFilter&) = delete;
+    OneEuroFilter(OneEuroFilter&&) = delete;
+    OneEuroFilter& operator=(OneEuroFilter&&) = delete;
+
+    /**
+     * Returns the filtered value of rawPosition. Each call to filter must provide a timestamp
+     * strictly greater than the timestamp of the previous call. The first time the method is
+     * called, it returns the value of rawPosition. Any subsequent calls provide a filtered value.
+     *
+     * @param timestamp The timestamp at which to filter. It must be strictly greater than the one
+     * provided in the previous call.
+     * @param rawPosition Position to be filtered.
+     */
+    float filter(std::chrono::duration<float> timestamp, float rawPosition);
+
+private:
+    /**
+     * Minimum cutoff frequency. This is the constant term in the adaptive cutoff frequency
+     * criterion. Units are Hertz.
+     */
+    const float mMinCutoffFreq;
+
+    /**
+     * Slope of the cutoff frequency criterion. This is the term scaling the absolute value of the
+     * filtered signal's speed. The data member is dimensionless, that is, it does not have units.
+     */
+    const float mBeta;
+
+    /**
+     * Cutoff frequency of the signal's speed. This is the cutoff frequency applied to the filtering
+     * of the signal's speed. Units are Hertz.
+     */
+    const float mSpeedCutoffFreq;
+
+    /**
+     * The timestamp from the previous call. Units are seconds.
+     */
+    std::optional<std::chrono::duration<float>> mPrevTimestamp;
+
+    /**
+     * The raw position from the previous call.
+     */
+    std::optional<float> mPrevRawPosition;
+
+    /**
+     * The filtered velocity from the previous call. Units are position per second.
+     */
+    std::optional<float> mPrevFilteredVelocity;
+
+    /**
+     * The filtered position from the previous call.
+     */
+    std::optional<float> mPrevFilteredPosition;
+};
+
+} // namespace android

include/input/Resampler.h

@@ -19,11 +19,13 @@
 #include <array>
 #include <chrono>
 #include <iterator>
+#include <map>
 #include <optional>
 #include <vector>
 
 #include <android-base/logging.h>
 #include <ftl/mixins.h>
+#include <input/CoordinateFilter.h>
 #include <input/Input.h>
 #include <input/InputTransport.h>
 #include <input/RingBuffer.h>
@@ -293,4 +295,43 @@ class LegacyResampler final : public Resampler {
     inline static void addSampleToMotionEvent(const Sample& sample, MotionEvent& motionEvent);
 };
 
+/**
+ * Resampler that first applies the LegacyResampler resampling algorithm, then independently filters
+ * the X and Y coordinates with a pair of One Euro filters.
+ */
+class FilteredLegacyResampler final : public Resampler {
+public:
+    /**
+     * Creates a resampler, using the given minCutoffFreq and beta to instantiate its One Euro
+     * filters.
+     */
+    explicit FilteredLegacyResampler(float minCutoffFreq, float beta);
+
+    void resampleMotionEvent(std::chrono::nanoseconds requestedFrameTime, MotionEvent& motionEvent,
+                             const InputMessage* futureMessage) override;
+
+    std::chrono::nanoseconds getResampleLatency() const override;
+
+private:
+    LegacyResampler mResampler;
+
+    /**
+     * Minimum cutoff frequency of the value's low pass filter. Refer to OneEuroFilter class for a
+     * more detailed explanation.
+     */
+    const float mMinCutoffFreq;
+
+    /**
+     * Scaling factor of the adaptive cutoff frequency criterion. Refer to OneEuroFilter class for a
+     * more detailed explanation.
+     */
+    const float mBeta;
+
+    /*
+     * Note: an associative array with constant insertion and lookup times would be more efficient.
+     * When this was implemented, there was no container with these properties.
+     */
+    std::map<int32_t /*pointerId*/, CoordinateFilter> mFilteredPointers;
+};
+
 } // namespace android

libs/input/Android.bp

@@ -217,6 +217,7 @@ cc_library {
     ],
     srcs: [
         "AccelerationCurve.cpp",
+        "CoordinateFilter.cpp",
         "Input.cpp",
         "InputConsumer.cpp",
         "InputConsumerNoResampling.cpp",
@@ -230,6 +231,7 @@ cc_library {
         "KeyLayoutMap.cpp",
         "MotionPredictor.cpp",
         "MotionPredictorMetricsManager.cpp",
+        "OneEuroFilter.cpp",
         "PrintTools.cpp",
         "PropertyMap.cpp",
         "Resampler.cpp",

libs/input/CoordinateFilter.cpp

@@ -0,0 +1,31 @@
+/**
+ * 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 "CoordinateFilter"
+
+#include <input/CoordinateFilter.h>
+
+namespace android {
+
+CoordinateFilter::CoordinateFilter(float minCutoffFreq, float beta)
+      : mXFilter{minCutoffFreq, beta}, mYFilter{minCutoffFreq, beta} {}
+
+void CoordinateFilter::filter(std::chrono::duration<float> timestamp, PointerCoords& coords) {
+    coords.setAxisValue(AMOTION_EVENT_AXIS_X, mXFilter.filter(timestamp, coords.getX()));
+    coords.setAxisValue(AMOTION_EVENT_AXIS_Y, mYFilter.filter(timestamp, coords.getY()));
+}
+
+} // namespace android

libs/input/OneEuroFilter.cpp

@@ -0,0 +1,79 @@
+/**
+ * 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 "OneEuroFilter"
+
+#include <chrono>
+#include <cmath>
+
+#include <android-base/logging.h>
+#include <input/CoordinateFilter.h>
+
+namespace android {
+namespace {
+
+inline float cutoffFreq(float minCutoffFreq, float beta, float filteredSpeed) {
+    return minCutoffFreq + beta * std::abs(filteredSpeed);
+}
+
+inline float smoothingFactor(std::chrono::duration<float> samplingPeriod, float cutoffFreq) {
+    return samplingPeriod.count() / (samplingPeriod.count() + (1.0 / (2.0 * M_PI * cutoffFreq)));
+}
+
+inline float lowPassFilter(float rawPosition, float prevFilteredPosition, float smoothingFactor) {
+    return smoothingFactor * rawPosition + (1 - smoothingFactor) * prevFilteredPosition;
+}
+
+} // namespace
+
+OneEuroFilter::OneEuroFilter(float minCutoffFreq, float beta, float speedCutoffFreq)
+      : mMinCutoffFreq{minCutoffFreq}, mBeta{beta}, mSpeedCutoffFreq{speedCutoffFreq} {}
+
+float OneEuroFilter::filter(std::chrono::duration<float> timestamp, float rawPosition) {
+    LOG_IF(FATAL, mPrevFilteredPosition.has_value() && (timestamp <= *mPrevTimestamp))
+            << "Timestamp must be greater than mPrevTimestamp";
+
+    const std::chrono::duration<float> samplingPeriod = (mPrevTimestamp.has_value())
+            ? (timestamp - *mPrevTimestamp)
+            : std::chrono::duration<float>{1.0};
+
+    const float rawVelocity = (mPrevFilteredPosition.has_value())
+            ? ((rawPosition - *mPrevFilteredPosition) / samplingPeriod.count())
+            : 0.0;
+
+    const float speedSmoothingFactor = smoothingFactor(samplingPeriod, mSpeedCutoffFreq);
+
+    const float filteredVelocity = (mPrevFilteredVelocity.has_value())
+            ? lowPassFilter(rawVelocity, *mPrevFilteredVelocity, speedSmoothingFactor)
+            : rawVelocity;
+
+    const float positionCutoffFreq = cutoffFreq(mMinCutoffFreq, mBeta, filteredVelocity);
+
+    const float positionSmoothingFactor = smoothingFactor(samplingPeriod, positionCutoffFreq);
+
+    const float filteredPosition = (mPrevFilteredPosition.has_value())
+            ? lowPassFilter(rawPosition, *mPrevFilteredPosition, positionSmoothingFactor)
+            : rawPosition;
+
+    mPrevTimestamp = timestamp;
+    mPrevRawPosition = rawPosition;
+    mPrevFilteredVelocity = filteredVelocity;
+    mPrevFilteredPosition = filteredPosition;
+
+    return filteredPosition;
+}
+
+} // namespace android

libs/input/Resampler.cpp

@@ -389,4 +389,34 @@ void LegacyResampler::resampleMotionEvent(nanoseconds frameTime, MotionEvent& mo
     mLastRealSample = *(mLatestSamples.end() - 1);
 }
 
+// --- FilteredLegacyResampler ---
+
+FilteredLegacyResampler::FilteredLegacyResampler(float minCutoffFreq, float beta)
+      : mResampler{}, mMinCutoffFreq{minCutoffFreq}, mBeta{beta} {}
+
+void FilteredLegacyResampler::resampleMotionEvent(std::chrono::nanoseconds requestedFrameTime,
+                                                  MotionEvent& motionEvent,
+                                                  const InputMessage* futureSample) {
+    mResampler.resampleMotionEvent(requestedFrameTime, motionEvent, futureSample);
+    const size_t numSamples = motionEvent.getHistorySize() + 1;
+    for (size_t sampleIndex = 0; sampleIndex < numSamples; ++sampleIndex) {
+        for (size_t pointerIndex = 0; pointerIndex < motionEvent.getPointerCount();
+             ++pointerIndex) {
+            const int32_t pointerId = motionEvent.getPointerProperties(pointerIndex)->id;
+            const nanoseconds eventTime =
+                    nanoseconds{motionEvent.getHistoricalEventTime(sampleIndex)};
+            // Refer to the static function `setMotionEventPointerCoords` for a justification of
+            // casting away const.
+            PointerCoords& pointerCoords = const_cast<PointerCoords&>(
+                    *(motionEvent.getHistoricalRawPointerCoords(pointerIndex, sampleIndex)));
+            const auto& [iter, _] = mFilteredPointers.try_emplace(pointerId, mMinCutoffFreq, mBeta);
+            iter->second.filter(eventTime, pointerCoords);
+        }
+    }
+}
+
+std::chrono::nanoseconds FilteredLegacyResampler::getResampleLatency() const {
+    return mResampler.getResampleLatency();
+}
+
 } // namespace android

libs/input/tests/Android.bp

@@ -25,6 +25,7 @@ cc_test {
         "InputVerifier_test.cpp",
         "MotionPredictor_test.cpp",
         "MotionPredictorMetricsManager_test.cpp",
+        "OneEuroFilter_test.cpp",
         "Resampler_test.cpp",
         "RingBuffer_test.cpp",
         "TestInputChannel.cpp",