Velocity Tracker II: The Revenge of Velocity Tracker

Bug: 5265529

Rewrote the velocity tracker to fit a polynomial curve
to pointer movements using least squares linear regression.
The velocity is simply the first derivative of this polynomial.

Clients can also obtain an Estimator that describes the
complete terms of the estimating polynomial including
the coefficient of determination which provides a measure
of the quality of the fit (confidence).

Enhanced PointerLocation to display the movement curve predicted
by the estimator in addition to the velocity vector.

By default, the algorithm computes a 2nd degree (quadratic)
polynomial based on a 100ms recent history horizon.

Change-Id: Id377bef44117fce68fee2c41f90134ce3224d3a1

1 files changed, 22 insertions, 2 deletions

diff --git a/core/java/com/android/internal/widget/PointerLocationView.java b/core/java/com/android/internal/widget/PointerLocationView.java
index 158291b..9a0ce3a 100644
--- a/core/java/com/android/internal/widget/PointerLocationView.java
+++ b/core/java/com/android/internal/widget/PointerLocationView.java
@@ -51,7 +51,10 @@ public class PointerLocationView extends View {
         // Most recent velocity.
         private float mXVelocity;
         private float mYVelocity;
-        
+
+        // Position estimator.
+        private VelocityTracker.Estimator mEstimator = new VelocityTracker.Estimator();
+
         public void clearTrace() {
             mTraceCount = 0;
         }
@@ -75,6 +78,10 @@ public class PointerLocationView extends View {
         }
     }
 
+    private final int ESTIMATE_PAST_POINTS = 4;
+    private final int ESTIMATE_FUTURE_POINTS = 2;
+    private final float ESTIMATE_INTERVAL = 0.02f;
+
     private final ViewConfiguration mVC;
     private final Paint mTextPaint;
     private final Paint mTextBackgroundPaint;
@@ -278,8 +285,20 @@ public class PointerLocationView extends View {
                     haveLast = true;
                 }
                 
-                // Draw velocity vector.
                 if (drawn) {
+                    // Draw movement estimate curve.
+                    mPaint.setARGB(128, 128, 0, 128);
+                    float lx = ps.mEstimator.estimateX(-ESTIMATE_PAST_POINTS * ESTIMATE_INTERVAL);
+                    float ly = ps.mEstimator.estimateY(-ESTIMATE_PAST_POINTS * ESTIMATE_INTERVAL);
+                    for (int i = -ESTIMATE_PAST_POINTS + 1; i <= ESTIMATE_FUTURE_POINTS; i++) {
+                        float x = ps.mEstimator.estimateX(i * ESTIMATE_INTERVAL);
+                        float y = ps.mEstimator.estimateY(i * ESTIMATE_INTERVAL);
+                        canvas.drawLine(lx, ly, x, y, mPaint);
+                        lx = x;
+                        ly = y;
+                    }
+
+                    // Draw velocity vector.
                     mPaint.setARGB(255, 255, 64, 128);
                     float xVel = ps.mXVelocity * (1000 / 60);
                     float yVel = ps.mYVelocity * (1000 / 60);
@@ -517,6 +536,7 @@ public class PointerLocationView extends View {
                     ps.addTrace(coords.x, coords.y);
                     ps.mXVelocity = mVelocity.getXVelocity(id);
                     ps.mYVelocity = mVelocity.getYVelocity(id);
+                    mVelocity.getEstimator(id, -1, -1, ps.mEstimator);
                     ps.mToolType = event.getToolType(i);
                 }
             }