Improve VelocityTracker Strategy Handling

The native VelocityTracker class has been made 1-dimensional to allow
support for axes beyond the historically-supported X/Y axes. This means
that a given VelocityTracker instance does not necessarily handle data
for all supported axes. As such, this CL sets up tracking strategy for
an axis only on the first occassion a data arrives for the axis.
Furthermore, to support use cases where different strategies may suit
different axes better, we have introduced per-axis default strategies.

Bug: 32830165
Test: atest libinput_tests; manual on-device fling tests
Change-Id: I3f7115fdcec78d1577e90e9a55175e8868bf2dfb
diff --git a/libs/input/VelocityTracker.cpp b/libs/input/VelocityTracker.cpp
index 6f88a38..527a75b 100644
--- a/libs/input/VelocityTracker.cpp
+++ b/libs/input/VelocityTracker.cpp
@@ -125,39 +125,32 @@
 
 // --- VelocityTracker ---
 
-const std::set<int32_t> VelocityTracker::SUPPORTED_AXES = {AMOTION_EVENT_AXIS_X,
-                                                           AMOTION_EVENT_AXIS_Y};
+const std::map<int32_t, VelocityTracker::Strategy> VelocityTracker::DEFAULT_STRATEGY_BY_AXIS =
+        {{AMOTION_EVENT_AXIS_X, VelocityTracker::Strategy::LSQ2},
+         {AMOTION_EVENT_AXIS_Y, VelocityTracker::Strategy::LSQ2}};
 
 const std::set<int32_t> VelocityTracker::PLANAR_AXES = {AMOTION_EVENT_AXIS_X, AMOTION_EVENT_AXIS_Y};
 
 VelocityTracker::VelocityTracker(const Strategy strategy)
-      : mLastEventTime(0), mCurrentPointerIdBits(0), mActivePointerId(-1) {
-    // Configure the strategy for each axis.
-    for (int32_t axis : SUPPORTED_AXES) {
-        configureStrategy(axis, strategy);
-    }
-}
+      : mLastEventTime(0),
+        mCurrentPointerIdBits(0),
+        mActivePointerId(-1),
+        mOverrideStrategy(strategy) {}
 
 VelocityTracker::~VelocityTracker() {
 }
 
-void VelocityTracker::configureStrategy(int32_t axis, const Strategy strategy) {
+void VelocityTracker::configureStrategy(int32_t axis) {
     std::unique_ptr<VelocityTrackerStrategy> createdStrategy;
-
-    if (strategy == VelocityTracker::Strategy::DEFAULT) {
-        createdStrategy = createStrategy(VelocityTracker::DEFAULT_STRATEGY);
+    if (mOverrideStrategy != VelocityTracker::Strategy::DEFAULT) {
+        createdStrategy = createStrategy(mOverrideStrategy);
     } else {
-        createdStrategy = createStrategy(strategy);
+        createdStrategy = createStrategy(VelocityTracker::DEFAULT_STRATEGY_BY_AXIS.at(axis));
     }
 
-    if (createdStrategy == nullptr) {
-        ALOGE("Unrecognized velocity tracker strategy %" PRId32 ".", strategy);
-        createdStrategy = createStrategy(VelocityTracker::DEFAULT_STRATEGY);
-        LOG_ALWAYS_FATAL_IF(createdStrategy == nullptr,
-                            "Could not create the default velocity tracker strategy '%" PRId32 "'!",
-                            strategy);
-    }
-    mStrategies[axis] = std::move(createdStrategy);
+    LOG_ALWAYS_FATAL_IF(createdStrategy == nullptr,
+                        "Could not create velocity tracker strategy for axis '%" PRId32 "'!", axis);
+    mConfiguredStrategies[axis] = std::move(createdStrategy);
 }
 
 std::unique_ptr<VelocityTrackerStrategy> VelocityTracker::createStrategy(
@@ -211,9 +204,7 @@
 void VelocityTracker::clear() {
     mCurrentPointerIdBits.clear();
     mActivePointerId = -1;
-    for (int32_t axis : SUPPORTED_AXES) {
-        mStrategies[axis]->clear();
-    }
+    mConfiguredStrategies.clear();
 }
 
 void VelocityTracker::clearPointers(BitSet32 idBits) {
@@ -224,8 +215,8 @@
         mActivePointerId = !remainingIdBits.isEmpty() ? remainingIdBits.firstMarkedBit() : -1;
     }
 
-    for (int32_t axis : SUPPORTED_AXES) {
-        mStrategies[axis]->clearPointers(idBits);
+    for (const auto& [_, strategy] : mConfiguredStrategies) {
+        strategy->clearPointers(idBits);
     }
 }
 
@@ -242,9 +233,7 @@
 
         // We have not received any movements for too long.  Assume that all pointers
         // have stopped.
-        for (const auto& [_, strategy] : mStrategies) {
-            strategy->clear();
-        }
+        mConfiguredStrategies.clear();
     }
     mLastEventTime = eventTime;
 
@@ -257,7 +246,10 @@
         LOG_ALWAYS_FATAL_IF(idBits.count() != positionValues.size(),
                             "Mismatching number of pointers, idBits=%" PRIu32 ", positions=%zu",
                             idBits.count(), positionValues.size());
-        mStrategies[axis]->addMovement(eventTime, idBits, positionValues);
+        if (mConfiguredStrategies.find(axis) == mConfiguredStrategies.end()) {
+            configureStrategy(axis);
+        }
+        mConfiguredStrategies[axis]->addMovement(eventTime, idBits, positionValues);
     }
 
     if (DEBUG_VELOCITY) {
@@ -323,7 +315,7 @@
             // We have not received any movements for too long.  Assume that all pointers
             // have stopped.
             for (int32_t axis : PLANAR_AXES) {
-                mStrategies[axis]->clear();
+                mConfiguredStrategies.erase(axis);
             }
         }
         // These actions because they do not convey any new information about
@@ -385,7 +377,7 @@
 VelocityTracker::ComputedVelocity VelocityTracker::getComputedVelocity(int32_t units,
                                                                        float maxVelocity) {
     ComputedVelocity computedVelocity;
-    for (int32_t axis : SUPPORTED_AXES) {
+    for (const auto& [axis, _] : mConfiguredStrategies) {
         BitSet32 copyIdBits = BitSet32(mCurrentPointerIdBits);
         while (!copyIdBits.isEmpty()) {
             uint32_t id = copyIdBits.clearFirstMarkedBit();
@@ -401,28 +393,22 @@
 }
 
 bool VelocityTracker::getEstimator(int32_t axis, uint32_t id, Estimator* outEstimator) const {
-    if (SUPPORTED_AXES.find(axis) == SUPPORTED_AXES.end()) {
+    const auto& it = mConfiguredStrategies.find(axis);
+    if (it == mConfiguredStrategies.end()) {
         return false;
     }
-    return mStrategies.at(axis)->getEstimator(id, outEstimator);
+    return it->second->getEstimator(id, outEstimator);
 }
 
 // --- LeastSquaresVelocityTrackerStrategy ---
 
-LeastSquaresVelocityTrackerStrategy::LeastSquaresVelocityTrackerStrategy(
-        uint32_t degree, Weighting weighting) :
-        mDegree(degree), mWeighting(weighting) {
-    clear();
-}
+LeastSquaresVelocityTrackerStrategy::LeastSquaresVelocityTrackerStrategy(uint32_t degree,
+                                                                         Weighting weighting)
+      : mDegree(degree), mWeighting(weighting), mIndex(0) {}
 
 LeastSquaresVelocityTrackerStrategy::~LeastSquaresVelocityTrackerStrategy() {
 }
 
-void LeastSquaresVelocityTrackerStrategy::clear() {
-    mIndex = 0;
-    mMovements[0].idBits.clear();
-}
-
 void LeastSquaresVelocityTrackerStrategy::clearPointers(BitSet32 idBits) {
     BitSet32 remainingIdBits(mMovements[mIndex].idBits.value & ~idBits.value);
     mMovements[mIndex].idBits = remainingIdBits;
@@ -825,10 +811,6 @@
 IntegratingVelocityTrackerStrategy::~IntegratingVelocityTrackerStrategy() {
 }
 
-void IntegratingVelocityTrackerStrategy::clear() {
-    mPointerIdBits.clear();
-}
-
 void IntegratingVelocityTrackerStrategy::clearPointers(BitSet32 idBits) {
     mPointerIdBits.value &= ~idBits.value;
 }
@@ -920,18 +902,11 @@
 
 // --- LegacyVelocityTrackerStrategy ---
 
-LegacyVelocityTrackerStrategy::LegacyVelocityTrackerStrategy() {
-    clear();
-}
+LegacyVelocityTrackerStrategy::LegacyVelocityTrackerStrategy() : mIndex(0) {}
 
 LegacyVelocityTrackerStrategy::~LegacyVelocityTrackerStrategy() {
 }
 
-void LegacyVelocityTrackerStrategy::clear() {
-    mIndex = 0;
-    mMovements[0].idBits.clear();
-}
-
 void LegacyVelocityTrackerStrategy::clearPointers(BitSet32 idBits) {
     BitSet32 remainingIdBits(mMovements[mIndex].idBits.value & ~idBits.value);
     mMovements[mIndex].idBits = remainingIdBits;
@@ -1029,18 +1004,11 @@
 
 // --- ImpulseVelocityTrackerStrategy ---
 
-ImpulseVelocityTrackerStrategy::ImpulseVelocityTrackerStrategy() {
-    clear();
-}
+ImpulseVelocityTrackerStrategy::ImpulseVelocityTrackerStrategy() : mIndex(0) {}
 
 ImpulseVelocityTrackerStrategy::~ImpulseVelocityTrackerStrategy() {
 }
 
-void ImpulseVelocityTrackerStrategy::clear() {
-    mIndex = 0;
-    mMovements[0].idBits.clear();
-}
-
 void ImpulseVelocityTrackerStrategy::clearPointers(BitSet32 idBits) {
     BitSet32 remainingIdBits(mMovements[mIndex].idBits.value & ~idBits.value);
     mMovements[mIndex].idBits = remainingIdBits;