1 files changed, 266 insertions, 0 deletions
diff --git a/libs/input/Resampler.cpp b/libs/input/Resampler.cpp
new file mode 100644
index 0000000000..51fadf8ec1
--- /dev/null
+++ b/libs/input/Resampler.cpp
@@ -0,0 +1,266 @@
+/**
+ * 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 <ftl/enum.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};
+
+bool canResampleTool(ToolType toolType) {
+    return toolType == ToolType::FINGER || toolType == ToolType::MOUSE ||
+            toolType == ToolType::STYLUS || toolType == ToolType::UNKNOWN;
+}
+
+inline float lerp(float a, float b, float alpha) {
+    return a + alpha * (b - a);
+}
+
+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;
+    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 numSamples = motionEvent.getHistorySize() + 1;
+    const size_t latestIndex = numSamples - 1;
+    const size_t secondToLatestIndex = (latestIndex > 0) ? (latestIndex - 1) : 0;
+    for (size_t sampleIndex = secondToLatestIndex; sampleIndex < numSamples; ++sampleIndex) {
+        std::vector<Pointer> pointers;
+        const size_t numPointers = motionEvent.getPointerCount();
+        for (size_t pointerIndex = 0; pointerIndex < numPointers; ++pointerIndex) {
+            // getSamplePointerCoords is the vector representation of a getHistorySize by
+            // getPointerCount matrix.
+            const PointerCoords& pointerCoords =
+                    motionEvent.getSamplePointerCoords()[sampleIndex * numPointers + pointerIndex];
+            pointers.push_back(
+                    Pointer{*motionEvent.getPointerProperties(pointerIndex), pointerCoords});
+        }
+        mLatestSamples.pushBack(
+                Sample{nanoseconds{motionEvent.getHistoricalEventTime(sampleIndex)}, pointers});
+    }
+}
+
+LegacyResampler::Sample LegacyResampler::messageToSample(const InputMessage& message) {
+    std::vector<Pointer> pointers;
+    for (uint32_t i = 0; i < message.body.motion.pointerCount; ++i) {
+        pointers.push_back(Pointer{message.body.motion.pointers[i].properties,
+                                   message.body.motion.pointers[i].coords});
+    }
+    return Sample{nanoseconds{message.body.motion.eventTime}, pointers};
+}
+
+bool LegacyResampler::pointerPropertiesResampleable(const Sample& target, const Sample& auxiliary) {
+    if (target.pointers.size() > auxiliary.pointers.size()) {
+        LOG_IF(INFO, debugResampling())
+                << "Not resampled. Auxiliary sample has fewer pointers than target sample.";
+        return false;
+    }
+    for (size_t i = 0; i < target.pointers.size(); ++i) {
+        if (target.pointers[i].properties.id != auxiliary.pointers[i].properties.id) {
+            LOG_IF(INFO, debugResampling()) << "Not resampled. Pointer ID mismatch.";
+            return false;
+        }
+        if (target.pointers[i].properties.toolType != auxiliary.pointers[i].properties.toolType) {
+            LOG_IF(INFO, debugResampling()) << "Not resampled. Pointer ToolType mismatch.";
+            return false;
+        }
+        if (!canResampleTool(target.pointers[i].properties.toolType)) {
+            LOG_IF(INFO, debugResampling())
+                    << "Not resampled. Cannot resample "
+                    << ftl::enum_string(target.pointers[i].properties.toolType) << " ToolType.";
+            return false;
+        }
+    }
+    return true;
+}
+
+bool LegacyResampler::canInterpolate(const InputMessage& message) const {
+    LOG_IF(FATAL, mLatestSamples.empty())
+            << "Not resampled. mLatestSamples must not be empty to interpolate.";
+
+    const Sample& pastSample = *(mLatestSamples.end() - 1);
+    const Sample& futureSample = messageToSample(message);
+
+    if (!pointerPropertiesResampleable(pastSample, futureSample)) {
+        return false;
+    }
+
+    const nanoseconds delta = futureSample.eventTime - pastSample.eventTime;
+    if (delta < RESAMPLE_MIN_DELTA) {
+        LOG_IF(INFO, debugResampling()) << "Not resampled. Delta is too small: " << delta << "ns.";
+        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 =
+            nanoseconds{futureSample.body.motion.eventTime} - pastSample.eventTime;
+    const float alpha =
+            std::chrono::duration<float, std::milli>(resampleTime - pastSample.eventTime) / delta;
+
+    std::vector<Pointer> resampledPointers;
+    for (size_t i = 0; i < pastSample.pointers.size(); ++i) {
+        const PointerCoords& resampledCoords =
+                calculateResampledCoords(pastSample.pointers[i].coords,
+                                         futureSample.body.motion.pointers[i].coords, alpha);
+        resampledPointers.push_back(Pointer{pastSample.pointers[i].properties, resampledCoords});
+    }
+    return Sample{resampleTime, resampledPointers};
+}
+
+bool LegacyResampler::canExtrapolate() const {
+    if (mLatestSamples.size() < 2) {
+        LOG_IF(INFO, debugResampling()) << "Not resampled. Not enough data.";
+        return false;
+    }
+
+    const Sample& pastSample = *(mLatestSamples.end() - 2);
+    const Sample& presentSample = *(mLatestSamples.end() - 1);
+
+    if (!pointerPropertiesResampleable(presentSample, pastSample)) {
+        return false;
+    }
+
+    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 false;
+    } else if (delta > RESAMPLE_MAX_DELTA) {
+        LOG_IF(INFO, debugResampling()) << "Not resampled. Delta is too large: " << delta << "ns.";
+        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 =
+            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;
+
+    std::vector<Pointer> resampledPointers;
+    for (size_t i = 0; i < presentSample.pointers.size(); ++i) {
+        const PointerCoords& resampledCoords =
+                calculateResampledCoords(pastSample.pointers[i].coords,
+                                         presentSample.pointers[i].coords, alpha);
+        resampledPointers.push_back(Pointer{presentSample.pointers[i].properties, resampledCoords});
+    }
+    return Sample{newResampleTime, resampledPointers};
+}
+
+inline void LegacyResampler::addSampleToMotionEvent(const Sample& sample,
+                                                    MotionEvent& motionEvent) {
+    motionEvent.addSample(sample.eventTime.count(), sample.asPointerCoords().data(),
+                          motionEvent.getId());
+}
+
+nanoseconds LegacyResampler::getResampleLatency() const {
+    return RESAMPLE_LATENCY;
+}
+
+void LegacyResampler::resampleMotionEvent(nanoseconds frameTime, MotionEvent& motionEvent,
+                                          const InputMessage* futureSample) {
+    if (mPreviousDeviceId && *mPreviousDeviceId != motionEvent.getDeviceId()) {
+        mLatestSamples.clear();
+    }
+    mPreviousDeviceId = motionEvent.getDeviceId();
+
+    const nanoseconds resampleTime = frameTime - RESAMPLE_LATENCY;
+
+    updateLatestSamples(motionEvent);
+
+    const std::optional<Sample> sample = (futureSample != nullptr)
+            ? (attemptInterpolation(resampleTime, *futureSample))
+            : (attemptExtrapolation(resampleTime));
+    if (sample.has_value()) {
+        addSampleToMotionEvent(*sample, motionEvent);
+    }
+}
+} // namespace android