Use touch pad gestures to manipulate the pointer.

1. Single finger tap performs a click.
2. Single finger movement moves the pointer (hovers).
3. Button press plus movement performs click or drag.
   While dragging, the pointer follows the finger that is moving
   fastest.  This is important if there are additional fingers
   down on the touch pad for the purpose of applying force
   to an integrated button underneath.
4. Two fingers near each other moving in the same direction
   are coalesced as a swipe gesture under the pointer.
5. Two or more fingers moving in arbitrary directions are
   transformed into touches in the vicinity of the pointer.
   This makes scale/zoom and rotate gestures possible.

Added a native VelocityTracker implementation to enable intelligent
switching of the active pointer during drags.

Change-Id: I5ada57e7f2bdb9b0a791843eb354a8c706b365dc

include/ui/Input.h

@@ -27,6 +27,7 @@
 #include <utils/Timers.h>
 #include <utils/RefBase.h>
 #include <utils/String8.h>
+#include <utils/BitSet.h>
 
 #ifdef HAVE_ANDROID_OS
 class SkMatrix;
@@ -208,6 +209,13 @@ struct PointerCoords {
     status_t writeToParcel(Parcel* parcel) const;
 #endif
 
+    bool operator==(const PointerCoords& other) const;
+    inline bool operator!=(const PointerCoords& other) const {
+        return !(*this == other);
+    }
+
+    void copyFrom(const PointerCoords& other);
+
 private:
     void tooManyAxes(int axis);
 };
@@ -542,6 +550,53 @@ private:
     MotionEvent mMotionEvent;
 };
 
+/*
+ * Calculates the velocity of pointer motions over time.
+ * Uses essentially the same algorithm as android.view.VelocityTracker.
+ */
+class VelocityTracker {
+public:
+    struct Position {
+        float x, y;
+    };
+
+    VelocityTracker();
+
+    // Resets the velocity tracker state.
+    void clear();
+
+    // Adds movement information for a set of pointers.
+    // The idBits bitfield specifies the pointer ids of the pointers whose positions
+    // are included in the movement.
+    // The positions array contains position information for each pointer in order by
+    // increasing id.  Its size should be equal to the number of one bits in idBits.
+    void addMovement(nsecs_t eventTime, BitSet32 idBits, const Position* positions);
+
+    // Gets the velocity of the specified pointer id in position units per second.
+    // Returns false and sets the velocity components to zero if there is no movement
+    // information for the pointer.
+    bool getVelocity(uint32_t id, float* outVx, float* outVy) const;
+
+private:
+    // Number of samples to keep.
+    static const uint32_t HISTORY_SIZE = 10;
+
+    // Oldest sample to consider when calculating the velocity.
+    static const nsecs_t MAX_AGE = 200 * 1000000; // 200 ms
+
+    // The minimum duration between samples when estimating velocity.
+    static const nsecs_t MIN_DURATION = 5 * 1000000; // 5 ms
+
+    struct Movement {
+        nsecs_t eventTime;
+        BitSet32 idBits;
+        Position positions[MAX_POINTERS];
+    };
+
+    uint32_t mIndex;
+    Movement mMovements[HISTORY_SIZE];
+};
+
 /*
  * Describes the characteristics and capabilities of an input device.
  */

include/utils/BitSet.h

@@ -61,6 +61,12 @@ struct BitSet32 {
     // Result is undefined if all bits are marked.
     inline uint32_t firstUnmarkedBit() const { return __builtin_clz(~ value); }
 
+    // Gets the index of the specified bit in the set, which is the number of
+    // marked bits that appear before the specified bit.
+    inline uint32_t getIndexOfBit(uint32_t n) const {
+        return __builtin_popcount(value & ~(0xffffffffUL >> n));
+    }
+
     inline bool operator== (const BitSet32& other) const { return value == other.value; }
     inline bool operator!= (const BitSet32& other) const { return value != other.value; }
 };

libs/ui/Input.cpp

@@ -7,8 +7,12 @@
 
 //#define LOG_NDEBUG 0
 
+// Log debug messages about keymap probing.
 #define DEBUG_PROBE 0
 
+// Log debug messages about velocity tracking.
+#define DEBUG_VELOCITY 0
+
 #include <stdlib.h>
 #include <unistd.h>
 #include <ctype.h>
@@ -329,6 +333,27 @@ void PointerCoords::tooManyAxes(int axis) {
             "cannot contain more than %d axis values.", axis, int(MAX_AXES));
 }
 
+bool PointerCoords::operator==(const PointerCoords& other) const {
+    if (bits != other.bits) {
+        return false;
+    }
+    uint32_t count = __builtin_popcountll(bits);
+    for (uint32_t i = 0; i < count; i++) {
+        if (values[i] != other.values[i]) {
+            return false;
+        }
+    }
+    return true;
+}
+
+void PointerCoords::copyFrom(const PointerCoords& other) {
+    bits = other.bits;
+    uint32_t count = __builtin_popcountll(bits);
+    for (uint32_t i = 0; i < count; i++) {
+        values[i] = other.values[i];
+    }
+}
+
 
 // --- MotionEvent ---
 
@@ -634,6 +659,135 @@ bool MotionEvent::isTouchEvent(int32_t source, int32_t action) {
 }
 
 
+// --- VelocityTracker ---
+
+VelocityTracker::VelocityTracker() {
+    clear();
+}
+
+void VelocityTracker::clear() {
+    mIndex = 0;
+    mMovements[0].idBits.clear();
+}
+
+void VelocityTracker::addMovement(nsecs_t eventTime, BitSet32 idBits, const Position* positions) {
+    if (++mIndex == HISTORY_SIZE) {
+        mIndex = 0;
+    }
+    Movement& movement = mMovements[mIndex];
+    movement.eventTime = eventTime;
+    movement.idBits = idBits;
+    uint32_t count = idBits.count();
+    for (uint32_t i = 0; i < count; i++) {
+        movement.positions[i] = positions[i];
+    }
+
+#if DEBUG_VELOCITY
+    LOGD("VelocityTracker: addMovement eventTime=%lld, idBits=0x%08x", eventTime, idBits.value);
+    for (BitSet32 iterBits(idBits); !iterBits.isEmpty(); ) {
+        uint32_t id = iterBits.firstMarkedBit();
+        uint32_t index = idBits.getIndexOfBit(id);
+        iterBits.clearBit(id);
+        float vx, vy;
+        bool available = getVelocity(id, &vx, &vy);
+        if (available) {
+            LOGD("  %d: position (%0.3f, %0.3f), velocity (%0.3f, %0.3f), speed %0.3f",
+                    id, positions[index].x, positions[index].y, vx, vy, sqrtf(vx * vx + vy * vy));
+        } else {
+            assert(vx == 0 && vy == 0);
+            LOGD("  %d: position (%0.3f, %0.3f), velocity not available",
+                    id, positions[index].x, positions[index].y);
+        }
+    }
+#endif
+}
+
+bool VelocityTracker::getVelocity(uint32_t id, float* outVx, float* outVy) const {
+    const Movement& newestMovement = mMovements[mIndex];
+    if (newestMovement.idBits.hasBit(id)) {
+        // Find the oldest sample that contains the pointer and that is not older than MAX_AGE.
+        nsecs_t minTime = newestMovement.eventTime - MAX_AGE;
+        uint32_t oldestIndex = mIndex;
+        uint32_t numTouches = 1;
+        do {
+            uint32_t nextOldestIndex = (oldestIndex == 0 ? HISTORY_SIZE : oldestIndex) - 1;
+            const Movement& nextOldestMovement = mMovements[nextOldestIndex];
+            if (!nextOldestMovement.idBits.hasBit(id)
+                    || nextOldestMovement.eventTime < minTime) {
+                break;
+            }
+            oldestIndex = nextOldestIndex;
+        } while (++numTouches < HISTORY_SIZE);
+
+        // If we have a lot of samples, skip the last received sample since it is
+        // probably pretty noisy compared to the sum of all of the traces already acquired.
+        //
+        // NOTE: This condition exists in the android.view.VelocityTracker and imposes a
+        // bias against the most recent data.
+        if (numTouches > 3) {
+            numTouches -= 1;
+        }
+
+        // Calculate an exponentially weighted moving average of the velocity at different
+        // points in time measured relative to the oldest samples.  This is essentially
+        // an IIR filter.
+        //
+        // One problem with this algorithm is that the sample data may be poorly conditioned.
+        // Sometimes samples arrive very close together in time which can cause us to
+        // overestimate the velocity at that time point.  Most samples might be measured
+        // 16ms apart but some consecutive samples could be only 0.5sm apart due to
+        // the way they are reported by the hardware or driver (sometimes in bursts or with
+        // significant jitter).  The instantaneous velocity for those samples 0.5ms apart will
+        // be calculated to be 32 times what it should have been.
+        // To work around this effect, we impose a minimum duration on the samples.
+        //
+        // FIXME: Samples close together in time can have an disproportionately large
+        // impact on the result because all samples are equally weighted.  The average should
+        // instead take the time factor into account.
+        //
+        // FIXME: The minimum duration condition does not exist in
+        // android.view.VelocityTracker yet.  It is less important there because sample times
+        // are truncated to the millisecond so back to back samples will often appear to be
+        // zero milliseconds apart and will be ignored if they are the oldest ones.
+        float accumVx = 0;
+        float accumVy = 0;
+        uint32_t index = oldestIndex;
+        uint32_t samplesUsed = 0;
+        const Movement& oldestMovement = mMovements[oldestIndex];
+        const Position& oldestPosition =
+                oldestMovement.positions[oldestMovement.idBits.getIndexOfBit(id)];
+        while (numTouches-- > 1) {
+            if (++index == HISTORY_SIZE) {
+                index = 0;
+            }
+            const Movement& movement = mMovements[index];
+            nsecs_t duration = movement.eventTime - oldestMovement.eventTime;
+            if (duration > MIN_DURATION) {
+                const Position& position = movement.positions[movement.idBits.getIndexOfBit(id)];
+                float scale = 1000000000.0f / duration; // one over time delta in seconds
+                float vx = (position.x - oldestPosition.x) * scale;
+                float vy = (position.y - oldestPosition.y) * scale;
+                accumVx = accumVx == 0 ? vx : (accumVx + vx) * 0.5f;
+                accumVy = accumVy == 0 ? vy : (accumVy + vy) * 0.5f;
+                samplesUsed += 1;
+            }
+        }
+
+        // Make sure we used at least one sample.
+        if (samplesUsed != 0) {
+            *outVx = accumVx;
+            *outVy = accumVy;
+            return true;
+        }
+    }
+
+    // No data available for this pointer.
+    *outVx = 0;
+    *outVy = 0;
+    return false;
+}
+
+
 // --- InputDeviceInfo ---
 
 InputDeviceInfo::InputDeviceInfo() {

libs/ui/InputTransport.cpp

@@ -406,7 +406,7 @@ status_t InputPublisher::publishMotionEvent(
 
     for (size_t i = 0; i < pointerCount; i++) {
         mSharedMessage->motion.pointerIds[i] = pointerIds[i];
-        mSharedMessage->motion.sampleData[0].coords[i] = pointerCoords[i];
+        mSharedMessage->motion.sampleData[0].coords[i].copyFrom(pointerCoords[i]);
     }
 
     // Cache essential information about the motion event to ensure that a malicious consumer
@@ -475,7 +475,7 @@ status_t InputPublisher::appendMotionSample(
 
     mMotionEventSampleDataTail->eventTime = eventTime;
     for (size_t i = 0; i < mMotionEventPointerCount; i++) {
-        mMotionEventSampleDataTail->coords[i] = pointerCoords[i];
+        mMotionEventSampleDataTail->coords[i].copyFrom(pointerCoords[i]);
     }
     mMotionEventSampleDataTail = newTail;