Fix One Euro filter's units of computation

Changed the units that the One Euro filter uses to compute the filtered
coordinates. This was causing a crash because if two timestamps were
sufficiently close to each other, by the time of implicitly converting
from nanoseconds to seconds, they were considered equal. This led to a
zero division when calculating the sampling frequency. Now, everything
is handled in the scale of nanoseconds, and conversion are done if and
only if they're necessary.

Bug: 297226446
Flag: EXEMPT bugfix
Test: TEST=libinput_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST
Change-Id: I7fced6db447074cccb3d938eb9dc7a9707433f53

8 files changed, 258 insertions, 23 deletions

diff --git a/include/input/CoordinateFilter.h b/include/input/CoordinateFilter.h
index f36472dc8c..8f2e605e85 100644
--- a/include/input/CoordinateFilter.h
+++ b/include/input/CoordinateFilter.h
@@ -44,7 +44,7 @@ public:
      * the previous call.
      * @param coords Coordinates to be overwritten by the corresponding filtered coordinates.
      */
-    void filter(std::chrono::duration<float> timestamp, PointerCoords& coords);
+    void filter(std::chrono::nanoseconds timestamp, PointerCoords& coords);
 
 private:
     OneEuroFilter mXFilter;
diff --git a/include/input/OneEuroFilter.h b/include/input/OneEuroFilter.h
index a0168e4f91..bdd82b2ee8 100644
--- a/include/input/OneEuroFilter.h
+++ b/include/input/OneEuroFilter.h
@@ -56,7 +56,7 @@ public:
      * provided in the previous call.
      * @param rawPosition Position to be filtered.
      */
-    float filter(std::chrono::duration<float> timestamp, float rawPosition);
+    float filter(std::chrono::nanoseconds timestamp, float rawPosition);
 
 private:
     /**
@@ -67,7 +67,7 @@ private:
 
     /**
      * 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.
+     * filtered signal's speed. Units are 1 / position.
      */
     const float mBeta;
 
@@ -78,9 +78,9 @@ private:
     const float mSpeedCutoffFreq;
 
     /**
-     * The timestamp from the previous call. Units are seconds.
+     * The timestamp from the previous call.
      */
-    std::optional<std::chrono::duration<float>> mPrevTimestamp;
+    std::optional<std::chrono::nanoseconds> mPrevTimestamp;
 
     /**
      * The raw position from the previous call.
@@ -88,7 +88,7 @@ private:
     std::optional<float> mPrevRawPosition;
 
     /**
-     * The filtered velocity from the previous call. Units are position per second.
+     * The filtered velocity from the previous call. Units are position per nanosecond.
      */
     std::optional<float> mPrevFilteredVelocity;
 
diff --git a/libs/input/CoordinateFilter.cpp b/libs/input/CoordinateFilter.cpp
index d231474577..a32685bd53 100644
--- a/libs/input/CoordinateFilter.cpp
+++ b/libs/input/CoordinateFilter.cpp
@@ -23,7 +23,7 @@ namespace android {
 CoordinateFilter::CoordinateFilter(float minCutoffFreq, float beta)
       : mXFilter{minCutoffFreq, beta}, mYFilter{minCutoffFreq, beta} {}
 
-void CoordinateFilter::filter(std::chrono::duration<float> timestamp, PointerCoords& coords) {
+void CoordinateFilter::filter(std::chrono::nanoseconds 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()));
 }
diff --git a/libs/input/OneEuroFilter.cpp b/libs/input/OneEuroFilter.cpp
index 400d7c9ab0..7b0d104da1 100644
--- a/libs/input/OneEuroFilter.cpp
+++ b/libs/input/OneEuroFilter.cpp
@@ -25,16 +25,24 @@
 namespace android {
 namespace {
 
+using namespace std::literals::chrono_literals;
+
+const float kHertzPerGigahertz = 1E9f;
+const float kGigahertzPerHertz = 1E-9f;
+
+// filteredSpeed's units are position per nanosecond. beta's units are 1 / position.
 inline float cutoffFreq(float minCutoffFreq, float beta, float filteredSpeed) {
-    return minCutoffFreq + beta * std::abs(filteredSpeed);
+    return kHertzPerGigahertz *
+            ((minCutoffFreq * kGigahertzPerHertz) + 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 smoothingFactor(std::chrono::nanoseconds samplingPeriod, float cutoffFreq) {
+    const float constant = 2.0f * M_PI * samplingPeriod.count() * (cutoffFreq * kGigahertzPerHertz);
+    return constant / (constant + 1);
 }
 
-inline float lowPassFilter(float rawPosition, float prevFilteredPosition, float smoothingFactor) {
-    return smoothingFactor * rawPosition + (1 - smoothingFactor) * prevFilteredPosition;
+inline float lowPassFilter(float rawValue, float prevFilteredValue, float smoothingFactor) {
+    return smoothingFactor * rawValue + (1 - smoothingFactor) * prevFilteredValue;
 }
 
 } // namespace
@@ -42,17 +50,17 @@ inline float lowPassFilter(float rawPosition, float prevFilteredPosition, float
 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";
+float OneEuroFilter::filter(std::chrono::nanoseconds timestamp, float rawPosition) {
+    LOG_IF(FATAL, mPrevTimestamp.has_value() && (*mPrevTimestamp >= timestamp))
+            << "Timestamp must be greater than mPrevTimestamp. Timestamp: " << timestamp.count()
+            << "ns. mPrevTimestamp: " << mPrevTimestamp->count() << "ns";
 
-    const std::chrono::duration<float> samplingPeriod = (mPrevTimestamp.has_value())
-            ? (timestamp - *mPrevTimestamp)
-            : std::chrono::duration<float>{1.0};
+    const std::chrono::nanoseconds samplingPeriod =
+            (mPrevTimestamp.has_value()) ? (timestamp - *mPrevTimestamp) : 1s;
 
     const float rawVelocity = (mPrevFilteredPosition.has_value())
-            ? ((rawPosition - *mPrevFilteredPosition) / samplingPeriod.count())
-            : 0.0;
+            ? ((rawPosition - *mPrevFilteredPosition) / (samplingPeriod.count()))
+            : 0.0f;
 
     const float speedSmoothingFactor = smoothingFactor(samplingPeriod, mSpeedCutoffFreq);
 
diff --git a/libs/input/tests/Android.bp b/libs/input/tests/Android.bp
index 46e819061f..d1c564d020 100644
--- a/libs/input/tests/Android.bp
+++ b/libs/input/tests/Android.bp
@@ -17,6 +17,7 @@ cc_test {
         "IdGenerator_test.cpp",
         "InputChannel_test.cpp",
         "InputConsumer_test.cpp",
+        "InputConsumerFilteredResampling_test.cpp",
         "InputConsumerResampling_test.cpp",
         "InputDevice_test.cpp",
         "InputEvent_test.cpp",
diff --git a/libs/input/tests/InputConsumerFilteredResampling_test.cpp b/libs/input/tests/InputConsumerFilteredResampling_test.cpp
new file mode 100644
index 0000000000..757cd18a38
--- /dev/null
+++ b/libs/input/tests/InputConsumerFilteredResampling_test.cpp
@@ -0,0 +1,218 @@
+/**
+ * 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/InputConsumerNoResampling.h>
+
+#include <chrono>
+#include <iostream>
+#include <memory>
+#include <queue>
+
+#include <TestEventMatchers.h>
+#include <TestInputChannel.h>
+#include <android-base/logging.h>
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+#include <input/Input.h>
+#include <input/InputEventBuilders.h>
+#include <input/Resampler.h>
+#include <utils/Looper.h>
+#include <utils/StrongPointer.h>
+
+namespace android {
+namespace {
+
+using std::chrono::nanoseconds;
+
+using ::testing::AllOf;
+using ::testing::Matcher;
+
+const int32_t ACTION_DOWN = AMOTION_EVENT_ACTION_DOWN;
+const int32_t ACTION_MOVE = AMOTION_EVENT_ACTION_MOVE;
+
+struct Pointer {
+    int32_t id{0};
+    ToolType toolType{ToolType::FINGER};
+    float x{0.0f};
+    float y{0.0f};
+    bool isResampled{false};
+
+    PointerBuilder asPointerBuilder() const {
+        return PointerBuilder{id, toolType}.x(x).y(y).isResampled(isResampled);
+    }
+};
+
+} // namespace
+
+class InputConsumerFilteredResamplingTest : public ::testing::Test, public InputConsumerCallbacks {
+protected:
+    InputConsumerFilteredResamplingTest()
+          : mClientTestChannel{std::make_shared<TestInputChannel>("TestChannel")},
+            mLooper{sp<Looper>::make(/*allowNonCallbacks=*/false)} {
+        Looper::setForThread(mLooper);
+        mConsumer = std::make_unique<
+                InputConsumerNoResampling>(mClientTestChannel, mLooper, *this, []() {
+            return std::make_unique<FilteredLegacyResampler>(/*minCutoffFreq=*/4.7, /*beta=*/0.01);
+        });
+    }
+
+    void invokeLooperCallback() const {
+        sp<LooperCallback> callback;
+        ASSERT_TRUE(mLooper->getFdStateDebug(mClientTestChannel->getFd(), /*ident=*/nullptr,
+                                             /*events=*/nullptr, &callback, /*data=*/nullptr));
+        ASSERT_NE(callback, nullptr);
+        callback->handleEvent(mClientTestChannel->getFd(), ALOOPER_EVENT_INPUT, /*data=*/nullptr);
+    }
+
+    void assertOnBatchedInputEventPendingWasCalled() {
+        ASSERT_GT(mOnBatchedInputEventPendingInvocationCount, 0UL)
+                << "onBatchedInputEventPending was not called";
+        --mOnBatchedInputEventPendingInvocationCount;
+    }
+
+    void assertReceivedMotionEvent(const Matcher<MotionEvent>& matcher) {
+        ASSERT_TRUE(!mMotionEvents.empty()) << "No motion events were received";
+        std::unique_ptr<MotionEvent> motionEvent = std::move(mMotionEvents.front());
+        mMotionEvents.pop();
+        ASSERT_NE(motionEvent, nullptr) << "The consumed motion event must not be nullptr";
+        EXPECT_THAT(*motionEvent, matcher);
+    }
+
+    InputMessage nextPointerMessage(nanoseconds eventTime, int32_t action, const Pointer& pointer);
+
+    std::shared_ptr<TestInputChannel> mClientTestChannel;
+    sp<Looper> mLooper;
+    std::unique_ptr<InputConsumerNoResampling> mConsumer;
+
+    // Batched input events
+    std::queue<std::unique_ptr<KeyEvent>> mKeyEvents;
+    std::queue<std::unique_ptr<MotionEvent>> mMotionEvents;
+    std::queue<std::unique_ptr<FocusEvent>> mFocusEvents;
+    std::queue<std::unique_ptr<CaptureEvent>> mCaptureEvents;
+    std::queue<std::unique_ptr<DragEvent>> mDragEvents;
+    std::queue<std::unique_ptr<TouchModeEvent>> mTouchModeEvents;
+
+private:
+    // InputConsumer callbacks
+    void onKeyEvent(std::unique_ptr<KeyEvent> event, uint32_t seq) override {
+        mKeyEvents.push(std::move(event));
+        mConsumer->finishInputEvent(seq, /*handled=*/true);
+    }
+
+    void onMotionEvent(std::unique_ptr<MotionEvent> event, uint32_t seq) override {
+        mMotionEvents.push(std::move(event));
+        mConsumer->finishInputEvent(seq, /*handled=*/true);
+    }
+
+    void onBatchedInputEventPending(int32_t pendingBatchSource) override {
+        if (!mConsumer->probablyHasInput()) {
+            ADD_FAILURE() << "Should deterministically have input because there is a batch";
+        }
+        ++mOnBatchedInputEventPendingInvocationCount;
+    }
+
+    void onFocusEvent(std::unique_ptr<FocusEvent> event, uint32_t seq) override {
+        mFocusEvents.push(std::move(event));
+        mConsumer->finishInputEvent(seq, /*handled=*/true);
+    }
+
+    void onCaptureEvent(std::unique_ptr<CaptureEvent> event, uint32_t seq) override {
+        mCaptureEvents.push(std::move(event));
+        mConsumer->finishInputEvent(seq, /*handled=*/true);
+    }
+
+    void onDragEvent(std::unique_ptr<DragEvent> event, uint32_t seq) override {
+        mDragEvents.push(std::move(event));
+        mConsumer->finishInputEvent(seq, /*handled=*/true);
+    }
+
+    void onTouchModeEvent(std::unique_ptr<TouchModeEvent> event, uint32_t seq) override {
+        mTouchModeEvents.push(std::move(event));
+        mConsumer->finishInputEvent(seq, /*handled=*/true);
+    }
+
+    uint32_t mLastSeq{0};
+    size_t mOnBatchedInputEventPendingInvocationCount{0};
+};
+
+InputMessage InputConsumerFilteredResamplingTest::nextPointerMessage(nanoseconds eventTime,
+                                                                     int32_t action,
+                                                                     const Pointer& pointer) {
+    ++mLastSeq;
+    return InputMessageBuilder{InputMessage::Type::MOTION, mLastSeq}
+            .eventTime(eventTime.count())
+            .source(AINPUT_SOURCE_TOUCHSCREEN)
+            .action(action)
+            .pointer(pointer.asPointerBuilder())
+            .build();
+}
+
+TEST_F(InputConsumerFilteredResamplingTest, NeighboringTimestampsDoNotResultInZeroDivision) {
+    mClientTestChannel->enqueueMessage(
+            nextPointerMessage(0ms, ACTION_DOWN, Pointer{.x = 0.0f, .y = 0.0f}));
+
+    invokeLooperCallback();
+
+    assertReceivedMotionEvent(AllOf(WithMotionAction(ACTION_DOWN), WithSampleCount(1)));
+
+    const std::chrono::nanoseconds initialTime{56'821'700'000'000};
+
+    mClientTestChannel->enqueueMessage(nextPointerMessage(initialTime + 4'929'000ns, ACTION_MOVE,
+                                                          Pointer{.x = 1.0f, .y = 1.0f}));
+    mClientTestChannel->enqueueMessage(nextPointerMessage(initialTime + 9'352'000ns, ACTION_MOVE,
+                                                          Pointer{.x = 2.0f, .y = 2.0f}));
+    mClientTestChannel->enqueueMessage(nextPointerMessage(initialTime + 14'531'000ns, ACTION_MOVE,
+                                                          Pointer{.x = 3.0f, .y = 3.0f}));
+
+    invokeLooperCallback();
+    mConsumer->consumeBatchedInputEvents(initialTime.count() + 18'849'395 /*ns*/);
+
+    assertOnBatchedInputEventPendingWasCalled();
+    // Three samples are expected. The first two of the batch, and the resampled one. The
+    // coordinates of the resampled sample are hardcoded because the matcher requires them. However,
+    // the primary intention here is to check that the last sample is resampled.
+    assertReceivedMotionEvent(AllOf(WithMotionAction(ACTION_MOVE), WithSampleCount(3),
+                                    WithSample(/*sampleIndex=*/2,
+                                               Sample{initialTime + 13'849'395ns,
+                                                      {PointerArgs{.x = 1.3286f,
+                                                                   .y = 1.3286f,
+                                                                   .isResampled = true}}})));
+
+    mClientTestChannel->enqueueMessage(nextPointerMessage(initialTime + 20'363'000ns, ACTION_MOVE,
+                                                          Pointer{.x = 4.0f, .y = 4.0f}));
+    mClientTestChannel->enqueueMessage(nextPointerMessage(initialTime + 25'745'000ns, ACTION_MOVE,
+                                                          Pointer{.x = 5.0f, .y = 5.0f}));
+    // This sample is part of the stream of messages, but should not be consumed because its
+    // timestamp is greater than the ajusted frame time.
+    mClientTestChannel->enqueueMessage(nextPointerMessage(initialTime + 31'337'000ns, ACTION_MOVE,
+                                                          Pointer{.x = 6.0f, .y = 6.0f}));
+
+    invokeLooperCallback();
+    mConsumer->consumeBatchedInputEvents(initialTime.count() + 35'516'062 /*ns*/);
+
+    assertOnBatchedInputEventPendingWasCalled();
+    // Four samples are expected because the last sample of the previous batch was not consumed.
+    assertReceivedMotionEvent(AllOf(WithMotionAction(ACTION_MOVE), WithSampleCount(4)));
+
+    mClientTestChannel->assertFinishMessage(/*seq=*/1, /*handled=*/true);
+    mClientTestChannel->assertFinishMessage(/*seq=*/2, /*handled=*/true);
+    mClientTestChannel->assertFinishMessage(/*seq=*/3, /*handled=*/true);
+    mClientTestChannel->assertFinishMessage(/*seq=*/4, /*handled=*/true);
+    mClientTestChannel->assertFinishMessage(/*seq=*/5, /*handled=*/true);
+    mClientTestChannel->assertFinishMessage(/*seq=*/6, /*handled=*/true);
+}
+
+} // namespace android
diff --git a/libs/input/tests/OneEuroFilter_test.cpp b/libs/input/tests/OneEuroFilter_test.cpp
index 270e789c84..8645508ea7 100644
--- a/libs/input/tests/OneEuroFilter_test.cpp
+++ b/libs/input/tests/OneEuroFilter_test.cpp
@@ -98,7 +98,10 @@ protected:
         std::vector<Sample> filteredSignal;
         for (const Sample& sample : signal) {
             filteredSignal.push_back(
-                    Sample{sample.timestamp, mFilter.filter(sample.timestamp, sample.value)});
+                    Sample{sample.timestamp,
+                           mFilter.filter(std::chrono::duration_cast<std::chrono::nanoseconds>(
+                                                  sample.timestamp),
+                                          sample.value)});
         }
         return filteredSignal;
     }
diff --git a/libs/input/tests/TestEventMatchers.h b/libs/input/tests/TestEventMatchers.h
index 3589de599f..de96600f66 100644
--- a/libs/input/tests/TestEventMatchers.h
+++ b/libs/input/tests/TestEventMatchers.h
@@ -17,6 +17,7 @@
 #pragma once
 
 #include <chrono>
+#include <cmath>
 #include <ostream>
 #include <vector>
 
@@ -150,14 +151,18 @@ public:
              ++pointerIndex) {
             const PointerCoords& pointerCoords =
                     *(motionEvent.getHistoricalRawPointerCoords(pointerIndex, mSampleIndex));
-            if ((pointerCoords.getX() != mSample.pointers[pointerIndex].x) ||
-                (pointerCoords.getY() != mSample.pointers[pointerIndex].y)) {
+
+            if ((std::abs(pointerCoords.getX() - mSample.pointers[pointerIndex].x) >
+                 MotionEvent::ROUNDING_PRECISION) ||
+                (std::abs(pointerCoords.getY() - mSample.pointers[pointerIndex].y) >
+                 MotionEvent::ROUNDING_PRECISION)) {
                 *os << "sample coordinates mismatch at pointer index " << pointerIndex
                     << ". sample: (" << pointerCoords.getX() << ", " << pointerCoords.getY()
                     << ") expected: (" << mSample.pointers[pointerIndex].x << ", "
                     << mSample.pointers[pointerIndex].y << ")";
                 return false;
             }
+
             if (motionEvent.isResampled(pointerIndex, mSampleIndex) !=
                 mSample.pointers[pointerIndex].isResampled) {
                 *os << "resampling flag mismatch. sample: "