Merge "Added check to make orientation calculations more robust"

Author: Dianne Hackborn

core/java/android/view/WindowOrientationListener.java

@@ -234,6 +234,14 @@ static class SensorEventListenerImpl implements SensorEventListener {
         // high time constant.
         private static final float MAX_DEVIATION_FROM_GRAVITY = 1.5f;
 
+        // Minimum acceleration considered, in m/s^2. Below this threshold sensor noise will have
+        // significant impact on the calculations and in case of the vector (0, 0, 0) there is no
+        // defined rotation or tilt at all. Low or zero readings can happen when space travelling
+        // or free falling, but more commonly when shaking or getting bad readings from the sensor.
+        // The accelerometer is turned off when not used and polling it too soon after it is
+        // turned on may result in (0, 0, 0).
+        private static final float MIN_ABS_ACCELERATION = 1.5f;
+
         // Actual sampling period corresponding to SensorManager.SENSOR_DELAY_NORMAL.  There's no
         // way to get this information from SensorManager.
         // Note the actual period is generally 3-30ms larger than this depending on the device, but
@@ -347,6 +355,9 @@ public void onSensorChanged(SensorEvent event) {
             float deviation = Math.abs(magnitude - SensorManager.STANDARD_GRAVITY);
 
             handleAccelerationDistrust(deviation);
+            if (magnitude < MIN_ABS_ACCELERATION) {
+                return; // Ignore tilt and orientation when (0, 0, 0) or low reading
+            }
 
             // only filter tilt when we're accelerating
             float alpha = 1;