Detect when pointer has stopped moving.

Some input devices do not generate ACTION_MOVE events while all
pointers have stopped, thereby lulling the VelocityTracker into
a false sense of complacency.  Before handling the following sample,
reset the VelocityTracker state so as not to be influenced by
earlier samples before the pointer stopped.  The velocity after
stopping is assumed to be discontinuous.

Bug: 6413587
Change-Id: I6387bc036ff141d083d3d17a89e37eeaa3188349

1 files changed, 5 insertions, 1 deletions

diff --git a/include/androidfw/VelocityTracker.h b/include/androidfw/VelocityTracker.h
index 6964588..cbb0782 100644
--- a/include/androidfw/VelocityTracker.h
+++ b/include/androidfw/VelocityTracker.h
@@ -37,6 +37,9 @@ public:
     struct Estimator {
         static const size_t MAX_DEGREE = 2;
 
+        // Estimator time base.
+        nsecs_t time;
+
         // Polynomial coefficients describing motion in X and Y.
         float xCoeff[MAX_DEGREE + 1], yCoeff[MAX_DEGREE + 1];
 
@@ -48,6 +51,7 @@ public:
         float confidence;
 
         inline void clear() {
+            time = 0;
             degree = 0;
             confidence = 0;
             for (size_t i = 0; i <= MAX_DEGREE; i++) {
@@ -58,7 +62,6 @@ public:
     };
 
     VelocityTracker();
-    VelocityTracker(VelocityTrackerStrategy* strategy);
     ~VelocityTracker();
 
     // Resets the velocity tracker state.
@@ -96,6 +99,7 @@ public:
     inline BitSet32 getCurrentPointerIdBits() const { return mCurrentPointerIdBits; }
 
 private:
+    nsecs_t mLastEventTime;
     BitSet32 mCurrentPointerIdBits;
     int32_t mActivePointerId;
     VelocityTrackerStrategy* mStrategy;