diff options
author | Steve Howard <showard@google.com> | 2010-02-25 13:42:43 -0800 |
---|---|---|
committer | Android (Google) Code Review <android-gerrit@google.com> | 2010-02-25 13:42:43 -0800 |
commit | d82968d8d8f3ac5908e6cb76b6e8989092f41c27 (patch) | |
tree | 4f9ac796eebd7680cf2081d83c1b40feea058aba /core/java | |
parent | 277903f8d853297a1d22ea07e27e04d6534bc430 (diff) | |
parent | 1ba101f82eae4e54293428480fbcbfd1c58359c8 (diff) | |
download | frameworks_base-d82968d8d8f3ac5908e6cb76b6e8989092f41c27.zip frameworks_base-d82968d8d8f3ac5908e6cb76b6e8989092f41c27.tar.gz frameworks_base-d82968d8d8f3ac5908e6cb76b6e8989092f41c27.tar.bz2 |
Merge "Improve accelerometer-based orientation sensing."
Diffstat (limited to 'core/java')
-rwxr-xr-x | core/java/android/view/WindowOrientationListener.java | 234 |
1 files changed, 161 insertions, 73 deletions
diff --git a/core/java/android/view/WindowOrientationListener.java b/core/java/android/view/WindowOrientationListener.java index 2aba60b..6c58461 100755 --- a/core/java/android/view/WindowOrientationListener.java +++ b/core/java/android/view/WindowOrientationListener.java @@ -57,8 +57,12 @@ public abstract class WindowOrientationListener { * {@link android.hardware.SensorManager SensorManager}). Use the default * value of {@link android.hardware.SensorManager#SENSOR_DELAY_NORMAL * SENSOR_DELAY_NORMAL} for simple screen orientation change detection. + * + * This constructor is private since no one uses it and making it public would complicate + * things, since the lowpass filtering code depends on the actual sampling period, and there's + * no way to get the period from SensorManager based on the rate constant. */ - public WindowOrientationListener(Context context, int rate) { + private WindowOrientationListener(Context context, int rate) { mSensorManager = (SensorManager)context.getSystemService(Context.SENSOR_SERVICE); mRate = rate; mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER); @@ -107,94 +111,179 @@ public abstract class WindowOrientationListener { } 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); + + // Indices into SensorEvent.values private static final int _DATA_X = 0; private static final int _DATA_Y = 1; private static final int _DATA_Z = 2; - // Angle around x-asis that's considered almost too vertical. Beyond - // this angle will not result in any orientation changes. f phone faces uses, - // the device is leaning backward. - private static final int PIVOT_UPPER = 65; - // Angle about x-axis that's considered negative vertical. Beyond this - // angle will not result in any orientation changes. If phone faces uses, - // the device is leaning forward. - private static final int PIVOT_LOWER = -10; - static final int ROTATION_0 = 0; - static final int ROTATION_90 = 1; - static final int ROTATION_180 = 2; - static final int ROTATION_270 = 3; - int mRotation = ROTATION_0; - - // Threshold values defined for device rotation positions - // follow order ROTATION_0 .. ROTATION_270 - final int THRESHOLDS[][][] = new int[][][] { - {{60, 135}, {135, 225}, {225, 300}}, - {{0, 45}, {45, 135}, {135, 210}, {330, 360}}, - {{0, 45}, {45, 120}, {240, 315}, {315, 360}}, - {{0, 30}, {150, 225}, {225, 315}, {315, 360}} + + // Internal aliases for the four orientation states. ROTATION_0 = default portrait mode, + // ROTATION_90 = left side of device facing the sky, etc. + private static final int ROTATION_0 = 0; + private static final int ROTATION_90 = 1; + private static final int ROTATION_180 = 2; + private static final int ROTATION_270 = 3; + + // 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_180, 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 degreees for hysteresis. For ROTATION_180, + // however, we enforce stricter thresholds, pushing the thresholds 15 degrees closer to 180. + private final int[][][] THRESHOLDS = new int[][][] { + {{60, 165}, {165, 195}, {195, 300}}, + {{0, 45}, {45, 165}, {165, 195}, {330, 360}}, + {{0, 45}, {45, 135}, {225, 315}, {315, 360}}, + {{0, 30}, {165, 195}, {195, 315}, {315, 360}} }; - // Transform rotation ranges based on THRESHOLDS. This - // has to be in step with THESHOLDS - final int ROTATE_TO[][] = new int[][] { - {ROTATION_270, ROTATION_180, ROTATION_90}, - {ROTATION_0, ROTATION_270, ROTATION_180, ROTATION_0}, - {ROTATION_0, ROTATION_270, ROTATION_90, ROTATION_0}, - {ROTATION_0, ROTATION_180, ROTATION_90, ROTATION_0} + // See THRESHOLDS + private final int[][] ROTATE_TO = new int[][] { + {ROTATION_270, ROTATION_180, ROTATION_90}, + {ROTATION_0, ROTATION_270, ROTATION_180, ROTATION_0}, + {ROTATION_0, ROTATION_270, ROTATION_90, ROTATION_0}, + {ROTATION_0, ROTATION_180, ROTATION_90, ROTATION_0} }; - // Mapping into actual Surface rotation values - final int TRANSFORM_ROTATIONS[] = new int[]{Surface.ROTATION_0, - Surface.ROTATION_90, Surface.ROTATION_180, Surface.ROTATION_270}; + // 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; + + // 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 + // particular orientation here. + private final int[] MAX_TRANSITION_TILT = new int[] {MAX_TILT, MAX_TILT, 40, MAX_TILT}; + + // 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; + + // 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; + + // 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 + // that's not enough to significantly skew our results. + private static final int SAMPLING_PERIOD_MS = 200; + + // The following time constants are all used in low-pass filtering the accelerometer output. + // See http://en.wikipedia.org/wiki/Low-pass_filter#Discrete-time_realization for + // background. + + // When device is near-vertical (screen approximately facing the horizon) + private static final int DEFAULT_TIME_CONSTANT_MS = 200; + // When device is partially tilted towards the sky or ground + private static final int TILTED_TIME_CONSTANT_MS = 600; + // 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 float DEFAULT_LOWPASS_ALPHA = + (float) SAMPLING_PERIOD_MS / (DEFAULT_TIME_CONSTANT_MS + SAMPLING_PERIOD_MS); + private static final float TILTED_LOWPASS_ALPHA = + (float) SAMPLING_PERIOD_MS / (TILTED_TIME_CONSTANT_MS + SAMPLING_PERIOD_MS); + private static final float ACCELERATING_LOWPASS_ALPHA = + (float) SAMPLING_PERIOD_MS / (ACCELERATING_TIME_CONSTANT_MS + SAMPLING_PERIOD_MS); + + // The low-pass filtered accelerometer data + private float[] mFilteredVector = new float[] {0, 0, 0}; int getCurrentRotation() { - return TRANSFORM_ROTATIONS[mRotation]; + return SURFACE_ROTATIONS[mRotation]; } - - private void calculateNewRotation(int orientation, int zyangle) { - if (localLOGV) Log.i(TAG, orientation + ", " + zyangle + ", " + mRotation); - int rangeArr[][] = THRESHOLDS[mRotation]; + + private void calculateNewRotation(int orientation, int tiltAngle) { + if (localLOGV) Log.i(TAG, orientation + ", " + tiltAngle + ", " + mRotation); + int thresholdRanges[][] = THRESHOLDS[mRotation]; int row = -1; - for (int i = 0; i < rangeArr.length; i++) { - if ((orientation >= rangeArr[i][0]) && (orientation < rangeArr[i][1])) { + for (int i = 0; i < thresholdRanges.length; i++) { + if (orientation >= thresholdRanges[i][0] && orientation < thresholdRanges[i][1]) { row = i; break; } } - if (row != -1) { - // Find new rotation based on current rotation value. - // This also takes care of irregular rotations as well. - int rotation = ROTATE_TO[mRotation][row]; - if (localLOGV) Log.i(TAG, " new rotation = " + rotation); - if (rotation != mRotation) { - mRotation = rotation; - // Trigger orientation change - onOrientationChanged(TRANSFORM_ROTATIONS[rotation]); - } + if (row == -1) return; // no matching transition + + int rotation = ROTATE_TO[mRotation][row]; + if (tiltAngle > MAX_TRANSITION_TILT[rotation]) { + // tilted too far flat to go to this rotation + return; } + + if (localLOGV) Log.i(TAG, " new rotation = " + rotation); + mRotation = rotation; + onOrientationChanged(SURFACE_ROTATIONS[rotation]); + } + + private float lowpassFilter(float newValue, float oldValue, float alpha) { + return alpha * newValue + (1 - alpha) * oldValue; + } + + private float vectorMagnitude(float x, float y, float z) { + return (float) Math.sqrt(x*x + y*y + z*z); + } + + /** + * 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. + */ + private float tiltAngle(float z, float magnitude) { + return Math.abs((float) Math.asin(z / magnitude) * RADIANS_TO_DEGREES); } public void onSensorChanged(SensorEvent event) { - float[] values = event.values; - float X = values[_DATA_X]; - float Y = values[_DATA_Y]; - float Z = values[_DATA_Z]; - float OneEightyOverPi = 57.29577957855f; - float gravity = (float) Math.sqrt(X*X+Y*Y+Z*Z); - float zyangle = (float)Math.asin(Z/gravity)*OneEightyOverPi; - if ((zyangle <= PIVOT_UPPER) && (zyangle >= PIVOT_LOWER)) { - // Check orientation only if the phone is flat enough - // Don't trust the angle if the magnitude is small compared to the y value - float angle = (float)Math.atan2(Y, -X) * OneEightyOverPi; - int orientation = 90 - Math.round(angle); - // normalize to 0 - 359 range - while (orientation >= 360) { - orientation -= 360; - } - while (orientation < 0) { - orientation += 360; - } - calculateNewRotation(orientation, Math.round(zyangle)); + // the vector given in the SensorEvent points straight up (towards the sky) under ideal + // conditions (the phone is not accelerating). i'll call this upVector elsewhere. + float x = event.values[_DATA_X]; + float y = event.values[_DATA_Y]; + 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); + + float alpha = DEFAULT_LOWPASS_ALPHA; + if (tiltAngle > MAX_TILT) { + return; + } else if (deviation > MAX_DEVIATION_FROM_GRAVITY) { + alpha = ACCELERATING_LOWPASS_ALPHA; + } else if (tiltAngle > PARTIAL_TILT) { + 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; } + calculateNewRotation(orientation, Math.round(tiltAngle)); } public void onAccuracyChanged(Sensor sensor, int accuracy) { @@ -208,13 +297,12 @@ public abstract class WindowOrientationListener { public boolean canDetectOrientation() { return mSensor != null; } - + /** * Called when the rotation view of the device has changed. - * Can be either Surface.ROTATION_90 or Surface.ROTATION_0. - * @param rotation The new orientation of the device. * - * @see #ORIENTATION_UNKNOWN + * @param rotation The new orientation of the device, one of the Surface.ROTATION_* constants. + * @see Surface */ abstract public void onOrientationChanged(int rotation); } |