Slight improvement (hopefully) to orientation sensing. (5f531ae6) · Commits · e / os / android_frameworks_base

core/java/android/view/WindowOrientationListener.java

+188 −57

Original line number	Diff line number	Diff line
		@@ -68,7 +68,7 @@ public abstract class WindowOrientationListener {
		mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
		if (mSensor != null) {
		// Create listener only if sensors do exist
		mSensorEventListener = new SensorEventListenerImpl();
		mSensorEventListener = new SensorEventListenerImpl(this);
		}
		}

		@@ -110,7 +110,34 @@ public abstract class WindowOrientationListener {
		return -1;
		}

		class SensorEventListenerImpl implements SensorEventListener {
		/**
		* This class filters the raw accelerometer data and tries to detect actual changes in
		* orientation. This is a very ill-defined problem so there are a lot of tweakable parameters,
		* but here's the outline:
		*
		* - Convert the acceleromter vector from cartesian to spherical coordinates. Since we're
		* dealing with rotation of the device, this is the sensible coordinate system to work in. The
		* zenith direction is the Z-axis, i.e. the direction the screen is facing. The radial distance
		* is referred to as the magnitude below. The elevation angle is referred to as the "tilt"
		* below. The azimuth angle is referred to as the "orientation" below (and the azimuth axis is
		* the Y-axis). See http://en.wikipedia.org/wiki/Spherical_coordinate_system for reference.
		*
		* - Low-pass filter the tilt and orientation angles to avoid "twitchy" behavior.
		*
		* - When the orientation angle reaches a certain threshold, transition to the corresponding
		* orientation. These thresholds have some hysteresis built-in to avoid oscillation.
		*
		* - Use the magnitude to judge the accuracy of the data. Under ideal conditions, the magnitude
		* should equal to that of gravity. When it differs significantly, we know the device is under
		* external acceleration and we can't trust the data.
		*
		* - Use the tilt angle to judge the accuracy of orientation data. When the tilt angle is high
		* in magnitude, we distrust the orientation data, because when the device is nearly flat, small
		* physical movements produce large changes in orientation angle.
		*
		* Details are explained below.
		*/
		static class SensorEventListenerImpl implements SensorEventListener {
		// We work with all angles in degrees in this class.
		private static final float RADIANS_TO_DEGREES = (float) (180 / Math.PI);

		@@ -125,54 +152,50 @@ public abstract class WindowOrientationListener {
		private static final int ROTATION_90 = 1;
		private static final int ROTATION_270 = 2;

		// Current orientation state
		private int mRotation = ROTATION_0;

		// Mapping our internal aliases into actual Surface rotation values
		private final int[] SURFACE_ROTATIONS = new int[] {Surface.ROTATION_0, Surface.ROTATION_90,
		Surface.ROTATION_270};
		private static final int[] SURFACE_ROTATIONS = new int[] {
		Surface.ROTATION_0, Surface.ROTATION_90, Surface.ROTATION_270};

		// Threshold ranges of orientation angle to transition into other orientation states.
		// The first list is for transitions from ROTATION_0, the next for ROTATION_90, etc.
		// ROTATE_TO defines the orientation each threshold range transitions to, and must be kept
		// in sync with this.
		// The thresholds are nearly regular -- we generally transition about the halfway point
		// between two states with a swing of 30 degrees for hysteresis. For ROTATION_180,
		// however, we enforce stricter thresholds, pushing the thresholds 15 degrees closer to 180.
		private final int[][][] THRESHOLDS = new int[][][] {
		// We generally transition about the halfway point between two states with a swing of 30
		// degrees for hysteresis.
		private static final int[][][] THRESHOLDS = new int[][][] {
		{{60, 180}, {180, 300}},
		{{0, 30}, {195, 315}, {315, 360}},
		{{0, 45}, {45, 165}, {330, 360}},
		{{0, 30}, {195, 315}, {315, 360}}
		};

		// See THRESHOLDS
		private final int[][] ROTATE_TO = new int[][] {
		{ROTATION_270, ROTATION_90},
		private static final int[][] ROTATE_TO = new int[][] {
		{ROTATION_90, ROTATION_270},
		{ROTATION_0, ROTATION_270, ROTATION_0},
		{ROTATION_0, ROTATION_90, ROTATION_0}
		{ROTATION_0, ROTATION_90, ROTATION_0},
		};

		// Maximum absolute tilt angle at which to consider orientation changes. Beyond this (i.e.
		// when screen is facing the sky or ground), we refuse to make any orientation changes.
		private static final int MAX_TILT = 65;
		// Maximum absolute tilt angle at which to consider orientation data. Beyond this (i.e.
		// when screen is facing the sky or ground), we completely ignore orientation data.
		private static final int MAX_TILT = 75;

		// Additional limits on tilt angle to transition to each new orientation. We ignore all
		// vectors with tilt beyond MAX_TILT, but we can set stricter limits on transition to a
		// data with tilt beyond MAX_TILT, but we can set stricter limits on transitions to a
		// particular orientation here.
		private final int[] MAX_TRANSITION_TILT = new int[] {MAX_TILT, MAX_TILT, MAX_TILT};
		private static final int[] MAX_TRANSITION_TILT = new int[] {MAX_TILT, 65, 65};

		// Between this tilt angle and MAX_TILT, we'll allow orientation changes, but we'll filter
		// with a higher time constant, making us less sensitive to change. This primarily helps
		// prevent momentary orientation changes when placing a device on a table from the side (or
		// picking one up).
		private static final int PARTIAL_TILT = 45;
		private static final int PARTIAL_TILT = 50;

		// Maximum allowable deviation of the magnitude of the sensor vector from that of gravity,
		// in m/s^2. Beyond this, we assume the phone is under external forces and we can't trust
		// the sensor data. However, under constantly vibrating conditions (think car mount), we
		// still want to pick up changes, so rather than ignore the data, we filter it with a very
		// high time constant.
		private static final int MAX_DEVIATION_FROM_GRAVITY = 1;
		private static final float MAX_DEVIATION_FROM_GRAVITY = 1.5f;

		// Actual sampling period corresponding to SensorManager.SENSOR_DELAY_NORMAL. There's no
		// way to get this information from SensorManager.
		@@ -185,28 +208,46 @@ public abstract class WindowOrientationListener {
		// background.

		// When device is near-vertical (screen approximately facing the horizon)
		private static final int DEFAULT_TIME_CONSTANT_MS = 200;
		private static final int DEFAULT_TIME_CONSTANT_MS = 50;
		// When device is partially tilted towards the sky or ground
		private static final int TILTED_TIME_CONSTANT_MS = 600;
		private static final int TILTED_TIME_CONSTANT_MS = 300;
		// When device is under external acceleration, i.e. not just gravity. We heavily distrust
		// such readings.
		private static final int ACCELERATING_TIME_CONSTANT_MS = 5000;
		private static final int ACCELERATING_TIME_CONSTANT_MS = 2000;

		private static final float DEFAULT_LOWPASS_ALPHA =
		(float) SAMPLING_PERIOD_MS / (DEFAULT_TIME_CONSTANT_MS + SAMPLING_PERIOD_MS);
		computeLowpassAlpha(DEFAULT_TIME_CONSTANT_MS);
		private static final float TILTED_LOWPASS_ALPHA =
		(float) SAMPLING_PERIOD_MS / (TILTED_TIME_CONSTANT_MS + SAMPLING_PERIOD_MS);
		computeLowpassAlpha(TILTED_TIME_CONSTANT_MS);
		private static final float ACCELERATING_LOWPASS_ALPHA =
		(float) SAMPLING_PERIOD_MS / (ACCELERATING_TIME_CONSTANT_MS + SAMPLING_PERIOD_MS);
		computeLowpassAlpha(ACCELERATING_TIME_CONSTANT_MS);

		private WindowOrientationListener mOrientationListener;
		private int mRotation = ROTATION_0; // Current orientation state
		private float mTiltAngle = 0; // low-pass filtered
		private float mOrientationAngle = 0; // low-pass filtered

		/*
		* Each "distrust" counter represents our current level of distrust in the data based on
		* a certain signal. For each data point that is deemed unreliable based on that signal,
		* the counter increases; otherwise, the counter decreases. Exact rules vary.
		*/
		private int mAccelerationDistrust = 0; // based on magnitude != gravity
		private int mTiltDistrust = 0; // based on tilt close to +/- 90 degrees

		// The low-pass filtered accelerometer data
		private float[] mFilteredVector = new float[] {0, 0, 0};
		public SensorEventListenerImpl(WindowOrientationListener orientationListener) {
		mOrientationListener = orientationListener;
		}

		private static float computeLowpassAlpha(int timeConstantMs) {
		return (float) SAMPLING_PERIOD_MS / (timeConstantMs + SAMPLING_PERIOD_MS);
		}

		int getCurrentRotation() {
		return SURFACE_ROTATIONS[mRotation];
		}

		private void calculateNewRotation(int orientation, int tiltAngle) {
		private void calculateNewRotation(float orientation, float tiltAngle) {
		if (localLOGV) Log.i(TAG, orientation + ", " + tiltAngle + ", " + mRotation);
		int thresholdRanges[][] = THRESHOLDS[mRotation];
		int row = -1;
		@@ -226,7 +267,7 @@ public abstract class WindowOrientationListener {

		if (localLOGV) Log.i(TAG, " new rotation = " + rotation);
		mRotation = rotation;
		onOrientationChanged(SURFACE_ROTATIONS[rotation]);
		mOrientationListener.onOrientationChanged(getCurrentRotation());
		}

		private float lowpassFilter(float newValue, float oldValue, float alpha) {
		@@ -238,11 +279,11 @@ public abstract class WindowOrientationListener {
		}

		/**
		* Absolute angle between upVector and the x-y plane (the plane of the screen), in [0, 90].
		* 90 degrees = screen facing the sky or ground.
		* Angle between upVector and the x-y plane (the plane of the screen), in [-90, 90].
		* +/- 90 degrees = screen facing the sky or ground.
		*/
		private float tiltAngle(float z, float magnitude) {
		return Math.abs((float) Math.asin(z / magnitude) * RADIANS_TO_DEGREES);
		return (float) Math.asin(z / magnitude) * RADIANS_TO_DEGREES;
		}

		public void onSensorChanged(SensorEvent event) {
		@@ -253,34 +294,124 @@ public abstract class WindowOrientationListener {
		float z = event.values[_DATA_Z];
		float magnitude = vectorMagnitude(x, y, z);
		float deviation = Math.abs(magnitude - SensorManager.STANDARD_GRAVITY);
		float tiltAngle = tiltAngle(z, magnitude);

		handleAccelerationDistrust(deviation);

		// only filter tilt when we're accelerating
		float alpha = 1;
		if (mAccelerationDistrust > 0) {
		alpha = ACCELERATING_LOWPASS_ALPHA;
		}
		float newTiltAngle = tiltAngle(z, magnitude);
		mTiltAngle = lowpassFilter(newTiltAngle, mTiltAngle, alpha);

		float absoluteTilt = Math.abs(mTiltAngle);
		if (checkFullyTilted(absoluteTilt)) {
		return; // when fully tilted, ignore orientation entirely
		}

		float newOrientationAngle = computeNewOrientation(x, y);
		filterOrientation(absoluteTilt, newOrientationAngle);
		calculateNewRotation(mOrientationAngle, absoluteTilt);
		}

		/**
		* When accelerating, increment distrust; otherwise, decrement distrust. The idea is that
		* if a single jolt happens among otherwise good data, we should keep trusting the good
		* data. On the other hand, if a series of many bad readings comes in (as if the phone is
		* being rapidly shaken), we should wait until things "settle down", i.e. we get a string
		* of good readings.
		*
		* @param deviation absolute difference between the current magnitude and gravity
		*/
		private void handleAccelerationDistrust(float deviation) {
		if (deviation > MAX_DEVIATION_FROM_GRAVITY) {
		if (mAccelerationDistrust < 5) {
		mAccelerationDistrust++;
		}
		} else if (mAccelerationDistrust > 0) {
		mAccelerationDistrust--;
		}
		}

		/**
		* Check if the phone is tilted towards the sky or ground and handle that appropriately.
		* When fully tilted, we automatically push the tilt up to a fixed value; otherwise we
		* decrement it. The idea is to distrust the first few readings after the phone gets
		* un-tilted, no matter what, i.e. preventing an accidental transition when the phone is
		* picked up from a table.
		*
		* We also reset the orientation angle to the center of the current screen orientation.
		* Since there is no real orientation of the phone, we want to ignore the most recent sensor
		* data and reset it to this value to avoid a premature transition when the phone starts to
		* get un-tilted.
		*
		* @param absoluteTilt the absolute value of the current tilt angle
		* @return true if the phone is fully tilted
		*/
		private boolean checkFullyTilted(float absoluteTilt) {
		boolean fullyTilted = absoluteTilt > MAX_TILT;
		if (fullyTilted) {
		if (mRotation == ROTATION_0) {
		mOrientationAngle = 0;
		} else if (mRotation == ROTATION_90) {
		mOrientationAngle = 90;
		} else { // ROTATION_270
		mOrientationAngle = 270;
		}

		if (mTiltDistrust < 3) {
		mTiltDistrust = 3;
		}
		} else if (mTiltDistrust > 0) {
		mTiltDistrust--;
		}
		return fullyTilted;
		}

		/**
		* Angle between the x-y projection of upVector and the +y-axis, increasing
		* clockwise.
		* 0 degrees = speaker end towards the sky
		* 90 degrees = right edge of device towards the sky
		*/
		private float computeNewOrientation(float x, float y) {
		float orientationAngle = (float) -Math.atan2(-x, y) * RADIANS_TO_DEGREES;
		// atan2 returns [-180, 180]; normalize to [0, 360]
		if (orientationAngle < 0) {
		orientationAngle += 360;
		}
		return orientationAngle;
		}

		/**
		* Compute a new filtered orientation angle.
		*/
		private void filterOrientation(float absoluteTilt, float orientationAngle) {
		float alpha = DEFAULT_LOWPASS_ALPHA;
		if (tiltAngle > MAX_TILT) {
		return;
		} else if (deviation > MAX_DEVIATION_FROM_GRAVITY) {
		if (mTiltDistrust > 0 \|\| mAccelerationDistrust > 1) {
		// when fully tilted, or under more than a transient acceleration, distrust heavily
		alpha = ACCELERATING_LOWPASS_ALPHA;
		} else if (tiltAngle > PARTIAL_TILT) {
		} else if (absoluteTilt > PARTIAL_TILT \|\| mAccelerationDistrust == 1) {
		// when tilted partway, or under transient acceleration, distrust lightly
		alpha = TILTED_LOWPASS_ALPHA;
		}

		x = mFilteredVector[0] = lowpassFilter(x, mFilteredVector[0], alpha);
		y = mFilteredVector[1] = lowpassFilter(y, mFilteredVector[1], alpha);
		z = mFilteredVector[2] = lowpassFilter(z, mFilteredVector[2], alpha);
		magnitude = vectorMagnitude(x, y, z);
		tiltAngle = tiltAngle(z, magnitude);

		// Angle between the x-y projection of upVector and the +y-axis, increasing
		// counter-clockwise.
		// 0 degrees = speaker end towards the sky
		// 90 degrees = left edge of device towards the sky
		float orientationAngle = (float) Math.atan2(-x, y) * RADIANS_TO_DEGREES;
		int orientation = Math.round(orientationAngle);
		// atan2 returns (-180, 180]; normalize to [0, 360)
		if (orientation < 0) {
		orientation += 360;
		// since we're lowpass filtering a value with periodic boundary conditions, we need to
		// adjust the new value to filter in the right direction...
		float deltaOrientation = orientationAngle - mOrientationAngle;
		if (deltaOrientation > 180) {
		orientationAngle -= 360;
		} else if (deltaOrientation < -180) {
		orientationAngle += 360;
		}
		mOrientationAngle = lowpassFilter(orientationAngle, mOrientationAngle, alpha);
		// ...and then adjust back to ensure we're in the range [0, 360]
		if (mOrientationAngle > 360) {
		mOrientationAngle -= 360;
		} else if (mOrientationAngle < 0) {
		mOrientationAngle += 360;
		}
		calculateNewRotation(orientation, Math.round(tiltAngle));
		}

		public void onAccuracyChanged(Sensor sensor, int accuracy) {