Add resampling to InputConsumerNoResampling

Moved resampling into its own class and provided test coverage for it.

Bug: 297226446
Flag: EXEMPT refactor
Test: TEST=libinput_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST --gtest_filter="*ResamplingTest*"
Change-Id: Ic6227b05120395c96643ab05e1cda373dba59e19

8 files changed, 728 insertions, 10 deletions

diff --git a/include/input/InputConsumerNoResampling.h b/include/input/InputConsumerNoResampling.h
index ae8de5f411..65c2914b3c 100644
--- a/include/input/InputConsumerNoResampling.h
+++ b/include/input/InputConsumerNoResampling.h
@@ -17,6 +17,7 @@
 #pragma once
 
 #include <input/InputTransport.h>
+#include <input/Resampler.h>
 #include <utils/Looper.h>
 
 namespace android {
@@ -47,13 +48,13 @@ public:
 /**
  * Consumes input events from an input channel.
  *
- * This is a re-implementation of InputConsumer that does not have resampling at the current moment.
- * A lot of the higher-level logic has been folded into this class, to make it easier to use.
- * In the legacy class, InputConsumer, the consumption logic was partially handled in the jni layer,
- * as well as various actions like adding the fd to the Choreographer.
+ * This is a re-implementation of InputConsumer. At the moment it only supports resampling for
+ * single pointer events. A lot of the higher-level logic has been folded into this class, to make
+ * it easier to use. In the legacy class, InputConsumer, the consumption logic was partially handled
+ * in the jni layer, as well as various actions like adding the fd to the Choreographer.
  *
  * TODO(b/297226446): use this instead of "InputConsumer":
- * - Add resampling to this class
+ * - Add resampling for multiple pointer events.
  * - Allow various resampling strategies to be specified
  * - Delete the old "InputConsumer" and use this class instead, renaming it to "InputConsumer".
  * - Add tracing
@@ -64,8 +65,18 @@ public:
  */
 class InputConsumerNoResampling final {
 public:
+    /**
+     * @param callbacks are used to interact with InputConsumerNoResampling. They're called whenever
+     * the event is ready to consume.
+     * @param looper needs to be sp and not shared_ptr because it inherits from
+     * RefBase
+     * @param resampler the resampling strategy to use. If null, no resampling will be
+     * performed.
+     */
     explicit InputConsumerNoResampling(const std::shared_ptr<InputChannel>& channel,
-                                       sp<Looper> looper, InputConsumerCallbacks& callbacks);
+                                       sp<Looper> looper, InputConsumerCallbacks& callbacks,
+                                       std::unique_ptr<Resampler> resampler);
+
     ~InputConsumerNoResampling();
 
     /**
@@ -99,6 +110,7 @@ private:
     std::shared_ptr<InputChannel> mChannel;
     sp<Looper> mLooper;
     InputConsumerCallbacks& mCallbacks;
+    std::unique_ptr<Resampler> mResampler;
 
     // Looper-related infrastructure
     /**
diff --git a/include/input/Resampler.h b/include/input/Resampler.h
new file mode 100644
index 0000000000..ff9c4b0868
--- /dev/null
+++ b/include/input/Resampler.h
@@ -0,0 +1,115 @@
+/**
+ * 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>
+#include <input/InputTransport.h>
+#include <input/RingBuffer.h>
+#include <utils/Timers.h>
+
+namespace android {
+
+/**
+ * Resampler is an interface for resampling MotionEvents. Every resampling implementation
+ * must use this interface to enable resampling inside InputConsumer's logic.
+ */
+struct Resampler {
+    virtual ~Resampler() = default;
+
+    /**
+     * Tries to resample motionEvent at resampleTime. The provided resampleTime must be greater than
+     * the latest sample time of motionEvent. It is not guaranteed that resampling occurs at
+     * resampleTime. Interpolation may occur is futureSample is available. Otherwise, motionEvent
+     * may be resampled by another method, or not resampled at all. Furthermore, it is the
+     * implementer's responsibility to guarantee the following:
+     * - If resampling occurs, a single additional sample should be added to motionEvent. That is,
+     * if motionEvent had N samples before being passed to Resampler, then it will have N + 1
+     * 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,
+                                     MotionEvent& motionEvent,
+                                     const InputMessage* futureSample) = 0;
+};
+
+class LegacyResampler final : public Resampler {
+public:
+    /**
+     * Tries to resample `motionEvent` at `resampleTime` by adding a resampled sample at the end of
+     * `motionEvent` with eventTime equal to `resampleTime` and pointer coordinates determined by
+     * linear interpolation or linear extrapolation. An earlier `resampleTime` will be used if
+     * extrapolation takes place and `resampleTime` is too far in the future. If `futureSample` is
+     * not null, interpolation will occur. If `futureSample` is null and there is enough historical
+     * data, LegacyResampler will extrapolate. Otherwise, no resampling takes place and
+     * `motionEvent` is unmodified.
+     */
+    void resampleMotionEvent(const std::chrono::nanoseconds resampleTime, MotionEvent& motionEvent,
+                             const InputMessage* futureSample) override;
+
+private:
+    struct Pointer {
+        PointerProperties properties;
+        PointerCoords coords;
+    };
+
+    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} {}
+    };
+
+    /**
+     * Keeps track of the previous MotionEvent deviceId to enable comparison between the previous
+     * and the current deviceId.
+     */
+    std::optional<DeviceId> mPreviousDeviceId;
+
+    /**
+     * Up to two latest samples from MotionEvent. Updated every time resampleMotionEvent is called.
+     * Note: We store up to two samples in order to simplify the implementation. Although,
+     * calculations are possible with only one previous sample.
+     */
+    RingBuffer<Sample> mLatestSamples{/*capacity=*/2};
+
+    /**
+     * Adds up to mLatestSamples.capacity() of motionEvent's latest samples to mLatestSamples. (If
+     * motionEvent has fewer samples than mLatestSamples.capacity(), then the available samples are
+     * added to mLatestSamples.)
+     */
+    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.
+     */
+    void interpolate(const std::chrono::nanoseconds resampleTime, MotionEvent& motionEvent,
+                     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.
+     */
+    void extrapolate(const std::chrono::nanoseconds resampleTime, MotionEvent& motionEvent) const;
+};
+} // namespace android
\ No newline at end of file
diff --git a/libs/input/Android.bp b/libs/input/Android.bp
index 8fbf5c6a2e..e4e81adf58 100644
--- a/libs/input/Android.bp
+++ b/libs/input/Android.bp
@@ -232,6 +232,7 @@ cc_library {
         "MotionPredictorMetricsManager.cpp",
         "PrintTools.cpp",
         "PropertyMap.cpp",
+        "Resampler.cpp",
         "TfLiteMotionPredictor.cpp",
         "TouchVideoFrame.cpp",
         "VelocityControl.cpp",
diff --git a/libs/input/InputConsumerNoResampling.cpp b/libs/input/InputConsumerNoResampling.cpp
index c145d5c286..99ffa683dd 100644
--- a/libs/input/InputConsumerNoResampling.cpp
+++ b/libs/input/InputConsumerNoResampling.cpp
@@ -17,6 +17,8 @@
 #define LOG_TAG "InputTransport"
 #define ATRACE_TAG ATRACE_TAG_INPUT
 
+#include <chrono>
+
 #include <inttypes.h>
 
 #include <android-base/logging.h>
@@ -168,6 +170,10 @@ InputMessage createTimelineMessage(int32_t inputEventId, nsecs_t gpuCompletedTim
     return msg;
 }
 
+bool isPointerEvent(const MotionEvent& motionEvent) {
+    return (motionEvent.getSource() & AINPUT_SOURCE_CLASS_POINTER) == AINPUT_SOURCE_CLASS_POINTER;
+}
+
 } // namespace
 
 using android::base::Result;
@@ -177,8 +183,13 @@ using android::base::StringPrintf;
 
 InputConsumerNoResampling::InputConsumerNoResampling(const std::shared_ptr<InputChannel>& channel,
                                                      sp<Looper> looper,
-                                                     InputConsumerCallbacks& callbacks)
-      : mChannel(channel), mLooper(looper), mCallbacks(callbacks), mFdEvents(0) {
+                                                     InputConsumerCallbacks& callbacks,
+                                                     std::unique_ptr<Resampler> resampler)
+      : mChannel(channel),
+        mLooper(looper),
+        mCallbacks(callbacks),
+        mResampler(std::move(resampler)),
+        mFdEvents(0) {
     LOG_ALWAYS_FATAL_IF(mLooper == nullptr);
     mCallback = sp<LooperEventCallback>::make(
             std::bind(&InputConsumerNoResampling::handleReceiveCallback, this,
@@ -463,6 +474,15 @@ InputConsumerNoResampling::createBatchedMotionEvent(const nsecs_t frameTime,
         }
         messages.pop();
     }
+    // Check if resampling should be performed.
+    if (motionEvent != nullptr && isPointerEvent(*motionEvent) && mResampler != nullptr) {
+        InputMessage* futureSample = nullptr;
+        if (!messages.empty()) {
+            futureSample = &messages.front();
+        }
+        mResampler->resampleMotionEvent(static_cast<std::chrono::nanoseconds>(frameTime),
+                                        *motionEvent, futureSample);
+    }
     return std::make_pair(std::move(motionEvent), firstSeqForBatch);
 }
 
diff --git a/libs/input/Resampler.cpp b/libs/input/Resampler.cpp
new file mode 100644
index 0000000000..af8354c70c
--- /dev/null
+++ b/libs/input/Resampler.cpp
@@ -0,0 +1,151 @@
+/**
+ * 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
diff --git a/libs/input/tests/Android.bp b/libs/input/tests/Android.bp
index e9d799ed3f..132866bd99 100644
--- a/libs/input/tests/Android.bp
+++ b/libs/input/tests/Android.bp
@@ -23,6 +23,7 @@ cc_test {
         "InputVerifier_test.cpp",
         "MotionPredictor_test.cpp",
         "MotionPredictorMetricsManager_test.cpp",
+        "Resampler_test.cpp",
         "RingBuffer_test.cpp",
         "TfLiteMotionPredictor_test.cpp",
         "TouchResampling_test.cpp",
diff --git a/libs/input/tests/InputPublisherAndConsumerNoResampling_test.cpp b/libs/input/tests/InputPublisherAndConsumerNoResampling_test.cpp
index e7106135fd..467c3b46ce 100644
--- a/libs/input/tests/InputPublisherAndConsumerNoResampling_test.cpp
+++ b/libs/input/tests/InputPublisherAndConsumerNoResampling_test.cpp
@@ -396,8 +396,9 @@ void InputPublisherAndConsumerNoResamplingTest::handleMessage(const Message& mes
             break;
         }
         case LooperMessage::CREATE_CONSUMER: {
-            mConsumer = std::make_unique<InputConsumerNoResampling>(std::move(mClientChannel),
-                                                                    mLooper, *this);
+            mConsumer =
+                    std::make_unique<InputConsumerNoResampling>(std::move(mClientChannel), mLooper,
+                                                                *this, /*resampler=*/nullptr);
             break;
         }
         case LooperMessage::DESTROY_CONSUMER: {
diff --git a/libs/input/tests/Resampler_test.cpp b/libs/input/tests/Resampler_test.cpp
new file mode 100644
index 0000000000..e160ca06d0
--- /dev/null
+++ b/libs/input/tests/Resampler_test.cpp
@@ -0,0 +1,417 @@
+/**
+ * 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.
+ */
+
+#include <input/Resampler.h>
+
+#include <gtest/gtest.h>
+
+#include <chrono>
+#include <memory>
+#include <vector>
+
+#include <input/Input.h>
+#include <input/InputEventBuilders.h>
+#include <input/InputTransport.h>
+#include <utils/Timers.h>
+
+namespace android {
+
+namespace {
+
+using namespace std::literals::chrono_literals;
+
+constexpr float EPSILON = MotionEvent::ROUNDING_PRECISION;
+
+struct Pointer {
+    int32_t id{0};
+    ToolType toolType{ToolType::FINGER};
+    float x{0.0f};
+    float y{0.0f};
+    bool isResampled{false};
+    /**
+     * Converts from Pointer to PointerCoords. Enables calling LegacyResampler methods and
+     * assertions only with the relevant data for tests.
+     */
+    operator PointerCoords() const;
+};
+
+Pointer::operator PointerCoords() const {
+    PointerCoords pointerCoords;
+    pointerCoords.setAxisValue(AMOTION_EVENT_AXIS_X, x);
+    pointerCoords.setAxisValue(AMOTION_EVENT_AXIS_Y, y);
+    pointerCoords.isResampled = isResampled;
+    return pointerCoords;
+}
+
+struct InputSample {
+    std::chrono::milliseconds eventTime{0};
+    std::vector<Pointer> pointers{};
+    /**
+     * Converts from InputSample to InputMessage. Enables calling LegacyResampler methods only with
+     * the relevant data for tests.
+     */
+    operator InputMessage() const;
+};
+
+InputSample::operator InputMessage() const {
+    InputMessage message;
+    message.header.type = InputMessage::Type::MOTION;
+    message.body.motion.pointerCount = pointers.size();
+    message.body.motion.eventTime = static_cast<std::chrono::nanoseconds>(eventTime).count();
+    message.body.motion.source = AINPUT_SOURCE_CLASS_POINTER;
+    message.body.motion.downTime = 0;
+    const uint32_t pointerCount = message.body.motion.pointerCount;
+    for (uint32_t i = 0; i < pointerCount; ++i) {
+        message.body.motion.pointers[i].properties.id = pointers[i].id;
+        message.body.motion.pointers[i].properties.toolType = pointers[i].toolType;
+        message.body.motion.pointers[i].coords.setAxisValue(AMOTION_EVENT_AXIS_X, pointers[i].x);
+        message.body.motion.pointers[i].coords.setAxisValue(AMOTION_EVENT_AXIS_Y, pointers[i].y);
+        message.body.motion.pointers[i].coords.isResampled = pointers[i].isResampled;
+    }
+    return message;
+}
+
+struct InputStream {
+    std::vector<InputSample> samples{};
+    int32_t action{0};
+    DeviceId deviceId{0};
+    /**
+     * Converts from InputStream to MotionEvent. Enables calling LegacyResampler methods only with
+     * the relevant data for tests.
+     */
+    operator MotionEvent() const;
+};
+
+InputStream::operator MotionEvent() const {
+    const InputSample& firstSample{*samples.begin()};
+    MotionEventBuilder motionEventBuilder =
+            MotionEventBuilder(action, AINPUT_SOURCE_CLASS_POINTER)
+                    .downTime(0)
+                    .eventTime(static_cast<std::chrono::nanoseconds>(firstSample.eventTime).count())
+                    .deviceId(deviceId);
+    for (const Pointer& pointer : firstSample.pointers) {
+        const PointerBuilder pointerBuilder =
+                PointerBuilder(pointer.id, pointer.toolType).x(pointer.x).y(pointer.y);
+        motionEventBuilder.pointer(pointerBuilder);
+    }
+    MotionEvent motionEvent = motionEventBuilder.build();
+    const size_t numSamples = samples.size();
+    for (size_t i = 1; i < numSamples; ++i) {
+        std::vector<PointerCoords> pointersCoords{samples[i].pointers.begin(),
+                                                  samples[i].pointers.end()};
+        motionEvent.addSample(static_cast<std::chrono::nanoseconds>(samples[i].eventTime).count(),
+                              pointersCoords.data(), motionEvent.getId());
+    }
+    return motionEvent;
+}
+
+} // namespace
+
+class ResamplerTest : public testing::Test {
+protected:
+    ResamplerTest() : mResampler(std::make_unique<LegacyResampler>()) {}
+
+    ~ResamplerTest() override {}
+
+    void SetUp() override {}
+
+    void TearDown() override {}
+
+    std::unique_ptr<Resampler> mResampler;
+
+    MotionEvent buildMotionEvent(const int32_t action, const nsecs_t eventTime,
+                                 const std::vector<PointerBuilder>& pointers);
+
+    InputMessage createMessage(const uint32_t pointerCount, const nsecs_t eventTime,
+                               const int32_t action,
+                               const std::vector<PointerProperties>& properties,
+                               const std::vector<PointerCoords>& coords);
+
+    /**
+     * Checks that beforeCall and afterCall are equal except for the mutated attributes by addSample
+     * member function.
+     * @param beforeCall MotionEvent before passing it to resampleMotionEvent
+     * @param afterCall MotionEvent after passing it to resampleMotionEvent
+     */
+    void assertMotionEventMetaDataDidNotMutate(const MotionEvent& beforeCall,
+                                               const MotionEvent& afterCall);
+
+    /**
+     * Asserts the MotionEvent is resampled by checking an increment in history size and that the
+     * resampled coordinates are near the expected ones.
+     */
+    void assertMotionEventIsResampledAndCoordsNear(const MotionEvent& original,
+                                                   const MotionEvent& resampled,
+                                                   const PointerCoords& expectedCoords);
+
+    void assertMotionEventIsNotResampled(const MotionEvent& original,
+                                         const MotionEvent& notResampled);
+};
+
+MotionEvent ResamplerTest::buildMotionEvent(const int32_t action, const nsecs_t eventTime,
+                                            const std::vector<PointerBuilder>& pointerBuilders) {
+    MotionEventBuilder motionEventBuilder = MotionEventBuilder(action, AINPUT_SOURCE_CLASS_POINTER)
+                                                    .downTime(0)
+                                                    .eventTime(eventTime);
+    for (const PointerBuilder& pointerBuilder : pointerBuilders) {
+        motionEventBuilder.pointer(pointerBuilder);
+    }
+    return motionEventBuilder.build();
+}
+
+InputMessage ResamplerTest::createMessage(const uint32_t pointerCount, const nsecs_t eventTime,
+                                          const int32_t action,
+                                          const std::vector<PointerProperties>& properties,
+                                          const std::vector<PointerCoords>& coords) {
+    InputMessage message;
+    message.header.type = InputMessage::Type::MOTION;
+    message.body.motion.pointerCount = pointerCount;
+    message.body.motion.eventTime = eventTime;
+    message.body.motion.source = AINPUT_SOURCE_CLASS_POINTER;
+    message.body.motion.downTime = 0;
+    for (uint32_t i = 0; i < pointerCount; ++i) {
+        message.body.motion.pointers[i].properties = properties[i];
+        message.body.motion.pointers[i].coords = coords[i];
+    }
+    return message;
+}
+
+void ResamplerTest::assertMotionEventMetaDataDidNotMutate(const MotionEvent& beforeCall,
+                                                          const MotionEvent& afterCall) {
+    EXPECT_EQ(beforeCall.getDeviceId(), afterCall.getDeviceId());
+    EXPECT_EQ(beforeCall.getAction(), afterCall.getAction());
+    EXPECT_EQ(beforeCall.getActionButton(), afterCall.getActionButton());
+    EXPECT_EQ(beforeCall.getButtonState(), afterCall.getButtonState());
+    EXPECT_EQ(beforeCall.getFlags(), afterCall.getFlags());
+    EXPECT_EQ(beforeCall.getEdgeFlags(), afterCall.getEdgeFlags());
+    EXPECT_EQ(beforeCall.getClassification(), afterCall.getClassification());
+    EXPECT_EQ(beforeCall.getPointerCount(), afterCall.getPointerCount());
+    EXPECT_EQ(beforeCall.getMetaState(), afterCall.getMetaState());
+    EXPECT_EQ(beforeCall.getSource(), afterCall.getSource());
+    EXPECT_EQ(beforeCall.getXPrecision(), afterCall.getXPrecision());
+    EXPECT_EQ(beforeCall.getYPrecision(), afterCall.getYPrecision());
+    EXPECT_EQ(beforeCall.getDownTime(), afterCall.getDownTime());
+    EXPECT_EQ(beforeCall.getDisplayId(), afterCall.getDisplayId());
+}
+
+void ResamplerTest::assertMotionEventIsResampledAndCoordsNear(const MotionEvent& original,
+                                                              const MotionEvent& resampled,
+                                                              const PointerCoords& expectedCoords) {
+    assertMotionEventMetaDataDidNotMutate(original, resampled);
+    const size_t originalSampleSize = original.getHistorySize() + 1;
+    const size_t resampledSampleSize = resampled.getHistorySize() + 1;
+    EXPECT_EQ(originalSampleSize + 1, resampledSampleSize);
+    const PointerCoords& resampledCoords =
+            resampled.getSamplePointerCoords()[resampled.getHistorySize()];
+    EXPECT_TRUE(resampledCoords.isResampled);
+    EXPECT_NEAR(expectedCoords.getX(), resampledCoords.getX(), EPSILON);
+    EXPECT_NEAR(expectedCoords.getY(), resampledCoords.getY(), EPSILON);
+}
+
+void ResamplerTest::assertMotionEventIsNotResampled(const MotionEvent& original,
+                                                    const MotionEvent& notResampled) {
+    assertMotionEventMetaDataDidNotMutate(original, notResampled);
+    const size_t originalSampleSize = original.getHistorySize() + 1;
+    const size_t notResampledSampleSize = notResampled.getHistorySize() + 1;
+    EXPECT_EQ(originalSampleSize, notResampledSampleSize);
+}
+
+TEST_F(ResamplerTest, SinglePointerNotEnoughDataToResample) {
+    MotionEvent motionEvent =
+            InputStream{{{5ms, {{.id = 0, .x = 1.0f, .y = 1.0f, .isResampled = false}}}},
+                        AMOTION_EVENT_ACTION_MOVE,
+                        .deviceId = 0};
+    const MotionEvent originalMotionEvent = motionEvent;
+    mResampler->resampleMotionEvent(11ms, motionEvent, nullptr);
+    assertMotionEventIsNotResampled(originalMotionEvent, motionEvent);
+}
+
+TEST_F(ResamplerTest, SinglePointerDifferentDeviceIdBetweenMotionEvents) {
+    MotionEvent motionFromFirstDevice =
+            InputStream{{{4ms, {{.id = 0, .x = 1.0f, .y = 1.0f, .isResampled = false}}},
+                         {8ms, {{.id = 0, .x = 2.0f, .y = 2.0f, .isResampled = false}}}},
+                        AMOTION_EVENT_ACTION_MOVE,
+                        .deviceId = 0};
+    mResampler->resampleMotionEvent(10ms, motionFromFirstDevice, nullptr);
+    MotionEvent motionFromSecondDevice =
+            InputStream{{{11ms, {{.id = 0, .x = 1.0f, .y = 1.0f, .isResampled = false}}}},
+                        AMOTION_EVENT_ACTION_MOVE,
+                        .deviceId = 1};
+    const MotionEvent originalMotionEvent = motionFromSecondDevice;
+    mResampler->resampleMotionEvent(12ms, motionFromSecondDevice, nullptr);
+    // The MotionEvent should not be resampled because the second event came from a different device
+    // than the previous event.
+    assertMotionEventIsNotResampled(originalMotionEvent, motionFromSecondDevice);
+}
+
+// Increments of 16 ms for display refresh rate
+// Increments of 6 ms for input frequency
+// Resampling latency is known to be 5 ms
+// Therefore, first resampling time will be 11 ms
+
+/**
+ * Timeline
+ * ----+----------------------+---------+---------+---------+----------
+ *     0ms                   10ms      11ms      15ms      16ms
+ *    DOWN                   MOVE       |        MSG        |
+ *                                  resample              frame
+ * Resampling occurs at 11ms. It is possible to interpolate because there is a sample available
+ * after the resample time. It is assumed that the InputMessage frequency is 100Hz, and the frame
+ * frequency is 60Hz. This means the time between InputMessage samples is 10ms, and the time between
+ * frames is ~16ms. Resample time is frameTime - RESAMPLE_LATENCY. The resampled sample must be the
+ * last one in the batch to consume.
+ */
+TEST_F(ResamplerTest, SinglePointerSingleSampleInterpolation) {
+    MotionEvent motionEvent =
+            InputStream{{{10ms, {{.id = 0, .x = 1.0f, .y = 1.0f, .isResampled = false}}}},
+                        AMOTION_EVENT_ACTION_MOVE};
+    const InputMessage futureSample =
+            InputSample{15ms, {{.id = 0, .x = 2.0f, .y = 2.0f, .isResampled = false}}};
+
+    const MotionEvent originalMotionEvent = motionEvent;
+
+    mResampler->resampleMotionEvent(11ms, motionEvent, &futureSample);
+
+    assertMotionEventIsResampledAndCoordsNear(originalMotionEvent, motionEvent,
+                                              Pointer{.id = 0,
+                                                      .x = 1.2f,
+                                                      .y = 1.2f,
+                                                      .isResampled = true});
+}
+
+TEST_F(ResamplerTest, SinglePointerDeltaTooSmallInterpolation) {
+    MotionEvent motionEvent =
+            InputStream{{{10ms, {{.id = 0, .x = 1.0f, .y = 1.0f, .isResampled = false}}}},
+                        AMOTION_EVENT_ACTION_MOVE};
+    const InputMessage futureSample =
+            InputSample{11ms, {{.id = 0, .x = 2.0f, .y = 2.0f, .isResampled = false}}};
+
+    const MotionEvent originalMotionEvent = motionEvent;
+
+    mResampler->resampleMotionEvent(10'500'000ns, motionEvent, &futureSample);
+
+    assertMotionEventIsNotResampled(originalMotionEvent, motionEvent);
+}
+
+/**
+ * Tests extrapolation given two MotionEvents with a single sample.
+ */
+TEST_F(ResamplerTest, SinglePointerSingleSampleExtrapolation) {
+    MotionEvent previousMotionEvent =
+            InputStream{{{5ms, {{.id = 0, .x = 1.0f, .y = 1.0f, .isResampled = false}}}},
+                        AMOTION_EVENT_ACTION_MOVE};
+
+    mResampler->resampleMotionEvent(10ms, previousMotionEvent, nullptr);
+
+    MotionEvent motionEvent =
+            InputStream{{{10ms, {{.id = 0, .x = 1.0f, .y = 1.0f, .isResampled = false}}}},
+                        AMOTION_EVENT_ACTION_MOVE};
+
+    const MotionEvent originalMotionEvent = motionEvent;
+
+    mResampler->resampleMotionEvent(11ms, motionEvent, nullptr);
+
+    assertMotionEventIsResampledAndCoordsNear(originalMotionEvent, motionEvent,
+                                              Pointer{.id = 0,
+                                                      .x = 1.0f,
+                                                      .y = 1.0f,
+                                                      .isResampled = true});
+    // Integrity of the whole motionEvent
+    // History size should increment by 1
+    // Check if the resampled value is the last one
+    // Check if the resampleTime is correct
+    // Check if the PointerCoords are consistent with the other computations
+}
+
+TEST_F(ResamplerTest, SinglePointerMultipleSampleInterpolation) {
+    MotionEvent motionEvent =
+            InputStream{{{5ms, {{.id = 0, .x = 1.0f, .y = 1.0f, .isResampled = false}}},
+                         {10ms, {{.id = 0, .x = 2.0f, .y = 2.0f, .isResampled = false}}}},
+                        AMOTION_EVENT_ACTION_MOVE};
+    const InputMessage futureSample =
+            InputSample{15ms, {{.id = 0, .x = 3.0f, .y = 3.0f, .isResampled = false}}};
+
+    const MotionEvent originalMotionEvent = motionEvent;
+
+    mResampler->resampleMotionEvent(11ms, motionEvent, &futureSample);
+
+    assertMotionEventIsResampledAndCoordsNear(originalMotionEvent, motionEvent,
+                                              Pointer{.id = 0,
+                                                      .x = 2.2f,
+                                                      .y = 2.2f,
+                                                      .isResampled = true});
+}
+
+TEST_F(ResamplerTest, SinglePointerMultipleSampleExtrapolation) {
+    MotionEvent motionEvent =
+            InputStream{{{5ms, {{.id = 0, .x = 1.0f, .y = 1.0f, .isResampled = false}}},
+                         {10ms, {{.id = 0, .x = 2.0f, .y = 2.0f, .isResampled = false}}}},
+                        AMOTION_EVENT_ACTION_MOVE};
+
+    const MotionEvent originalMotionEvent = motionEvent;
+
+    mResampler->resampleMotionEvent(11ms, motionEvent, nullptr);
+
+    assertMotionEventIsResampledAndCoordsNear(originalMotionEvent, motionEvent,
+                                              Pointer{.id = 0,
+                                                      .x = 2.2f,
+                                                      .y = 2.2f,
+                                                      .isResampled = true});
+}
+
+TEST_F(ResamplerTest, SinglePointerDeltaTooSmallExtrapolation) {
+    MotionEvent motionEvent =
+            InputStream{{{9ms, {{.id = 0, .x = 1.0f, .y = 1.0f, .isResampled = false}}},
+                         {10ms, {{.id = 0, .x = 2.0f, .y = 2.0f, .isResampled = false}}}},
+                        AMOTION_EVENT_ACTION_MOVE};
+
+    const MotionEvent originalMotionEvent = motionEvent;
+
+    mResampler->resampleMotionEvent(11ms, motionEvent, nullptr);
+
+    assertMotionEventIsNotResampled(originalMotionEvent, motionEvent);
+}
+
+TEST_F(ResamplerTest, SinglePointerDeltaTooLargeExtrapolation) {
+    MotionEvent motionEvent =
+            InputStream{{{5ms, {{.id = 0, .x = 1.0f, .y = 1.0f, .isResampled = false}}},
+                         {26ms, {{.id = 0, .x = 2.0f, .y = 2.0f, .isResampled = false}}}},
+                        AMOTION_EVENT_ACTION_MOVE};
+
+    const MotionEvent originalMotionEvent = motionEvent;
+
+    mResampler->resampleMotionEvent(27ms, motionEvent, nullptr);
+
+    assertMotionEventIsNotResampled(originalMotionEvent, motionEvent);
+}
+
+TEST_F(ResamplerTest, SinglePointerResampleTimeTooFarExtrapolation) {
+    MotionEvent motionEvent =
+            InputStream{{{5ms, {{.id = 0, .x = 1.0f, .y = 1.0f, .isResampled = false}}},
+                         {25ms, {{.id = 0, .x = 2.0f, .y = 2.0f, .isResampled = false}}}},
+                        AMOTION_EVENT_ACTION_MOVE};
+
+    const MotionEvent originalMotionEvent = motionEvent;
+
+    mResampler->resampleMotionEvent(43ms, motionEvent, nullptr);
+
+    assertMotionEventIsResampledAndCoordsNear(originalMotionEvent, motionEvent,
+                                              Pointer{.id = 0,
+                                                      .x = 2.4f,
+                                                      .y = 2.4f,
+                                                      .isResampled = true});
+}
+} // namespace android