/*
* Copyright (C) 2008 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.view;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.SystemProperties;
import android.util.FloatMath;
import android.util.Log;
import android.util.Slog;
/**
* A special helper class used by the WindowManager
* for receiving notifications from the SensorManager when
* the orientation of the device has changed.
*
* NOTE: If changing anything here, please run the API demo
* "App/Activity/Screen Orientation" to ensure that all orientation
* modes still work correctly.
*
* You can also visualize the behavior of the WindowOrientationListener.
* Refer to frameworks/base/tools/orientationplot/README.txt for details.
*
* @hide
*/
public abstract class WindowOrientationListener {
private static final String TAG = "WindowOrientationListener";
private static final boolean LOG = SystemProperties.getBoolean(
"debug.orientation.log", false);
private static final boolean USE_GRAVITY_SENSOR = false;
private SensorManager mSensorManager;
private boolean mEnabled;
private int mRate;
private Sensor mSensor;
private SensorEventListenerImpl mSensorEventListener;
int mCurrentRotation = -1;
/**
* Creates a new WindowOrientationListener.
*
* @param context for the WindowOrientationListener.
*/
public WindowOrientationListener(Context context) {
this(context, SensorManager.SENSOR_DELAY_UI);
}
/**
* Creates a new WindowOrientationListener.
*
* @param context for the WindowOrientationListener.
* @param rate at which sensor events are processed (see also
* {@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.
*/
private WindowOrientationListener(Context context, int rate) {
mSensorManager = (SensorManager)context.getSystemService(Context.SENSOR_SERVICE);
mRate = rate;
mSensor = mSensorManager.getDefaultSensor(USE_GRAVITY_SENSOR
? Sensor.TYPE_GRAVITY : Sensor.TYPE_ACCELEROMETER);
if (mSensor != null) {
// Create listener only if sensors do exist
mSensorEventListener = new SensorEventListenerImpl(this);
}
}
/**
* Enables the WindowOrientationListener so it will monitor the sensor and call
* {@link #onOrientationChanged} when the device orientation changes.
*/
public void enable() {
if (mSensor == null) {
Log.w(TAG, "Cannot detect sensors. Not enabled");
return;
}
if (mEnabled == false) {
if (LOG) {
Log.d(TAG, "WindowOrientationListener enabled");
}
mSensorManager.registerListener(mSensorEventListener, mSensor, mRate);
mEnabled = true;
}
}
/**
* Disables the WindowOrientationListener.
*/
public void disable() {
if (mSensor == null) {
Log.w(TAG, "Cannot detect sensors. Invalid disable");
return;
}
if (mEnabled == true) {
if (LOG) {
Log.d(TAG, "WindowOrientationListener disabled");
}
mSensorManager.unregisterListener(mSensorEventListener);
mEnabled = false;
}
}
/**
* Sets the current rotation.
*
* @param rotation The current rotation.
*/
public void setCurrentRotation(int rotation) {
mCurrentRotation = rotation;
}
/**
* Gets the proposed rotation.
*
* This method only returns a rotation if the orientation listener is certain
* of its proposal. If the rotation is indeterminate, returns -1.
*
* @return The proposed rotation, or -1 if unknown.
*/
public int getProposedRotation() {
if (mEnabled) {
return mSensorEventListener.getProposedRotation();
}
return -1;
}
/**
* Returns true if sensor is enabled and false otherwise
*/
public boolean canDetectOrientation() {
return mSensor != null;
}
/**
* Called when the rotation view of the device has changed.
*
* This method is called whenever the orientation becomes certain of an orientation.
* It is called each time the orientation determination transitions from being
* uncertain to being certain again, even if it is the same orientation as before.
*
* @param rotation The new orientation of the device, one of the Surface.ROTATION_* constants.
* @see Surface
*/
public abstract void onProposedRotationChanged(int rotation);
/**
* 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:
*
* - Low-pass filter the accelerometer vector in cartesian coordinates. We do it in
* cartesian space because the orientation calculations are sensitive to the
* absolute magnitude of the acceleration. In particular, there are singularities
* in the calculation as the magnitude approaches 0. By performing the low-pass
* filtering early, we can eliminate most spurious high-frequency impulses due to noise.
*
* - 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, 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.
*
* - If the tilt angle is too close to horizontal (near 90 or -90 degrees), do nothing.
* The orientation angle is not meaningful when the device is nearly horizontal.
* The tilt angle thresholds are set differently for each orientation and different
* limits are applied when the device is facing down as opposed to when it is facing
* forward or facing up.
*
* - When the orientation angle reaches a certain threshold, consider transitioning
* to the corresponding orientation. These thresholds have some hysteresis built-in
* to avoid oscillations between adjacent orientations.
*
* - Wait for the device to settle for a little bit. Once that happens, issue the
* new orientation proposal.
*
* Details are explained inline.
*
* See http://en.wikipedia.org/wiki/Low-pass_filter#Discrete-time_realization for
* signal processing background.
*/
static final 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);
// Number of nanoseconds per millisecond.
private static final long NANOS_PER_MS = 1000000;
// Indices into SensorEvent.values for the accelerometer sensor.
private static final int ACCELEROMETER_DATA_X = 0;
private static final int ACCELEROMETER_DATA_Y = 1;
private static final int ACCELEROMETER_DATA_Z = 2;
private final WindowOrientationListener mOrientationListener;
// The minimum amount of time that a predicted rotation must be stable before it
// is accepted as a valid rotation proposal. This value can be quite small because
// the low-pass filter already suppresses most of the noise so we're really just
// looking for quick confirmation that the last few samples are in agreement as to
// the desired orientation.
private static final long PROPOSAL_SETTLE_TIME_NANOS = 40 * NANOS_PER_MS;
// The minimum amount of time that must have elapsed since the device last exited
// the flat state (time since it was picked up) before the proposed rotation
// can change.
private static final long PROPOSAL_MIN_TIME_SINCE_FLAT_ENDED_NANOS = 500 * NANOS_PER_MS;
// The minimum amount of time that must have elapsed since the device stopped
// swinging (time since device appeared to be in the process of being put down
// or put away into a pocket) before the proposed rotation can change.
private static final long PROPOSAL_MIN_TIME_SINCE_SWING_ENDED_NANOS = 300 * NANOS_PER_MS;
// The minimum amount of time that must have elapsed since the device stopped
// undergoing external acceleration before the proposed rotation can change.
private static final long PROPOSAL_MIN_TIME_SINCE_ACCELERATION_ENDED_NANOS =
500 * NANOS_PER_MS;
// If the tilt angle remains greater than the specified angle for a minimum of
// the specified time, then the device is deemed to be lying flat
// (just chillin' on a table).
private static final float FLAT_ANGLE = 75;
private static final long FLAT_TIME_NANOS = 1000 * NANOS_PER_MS;
// If the tilt angle has increased by at least delta degrees within the specified amount
// of time, then the device is deemed to be swinging away from the user
// down towards flat (tilt = 90).
private static final float SWING_AWAY_ANGLE_DELTA = 20;
private static final long SWING_TIME_NANOS = 300 * NANOS_PER_MS;
// The maximum sample inter-arrival time in milliseconds.
// If the acceleration samples are further apart than this amount in time, we reset the
// state of the low-pass filter and orientation properties. This helps to handle
// boundary conditions when the device is turned on, wakes from suspend or there is
// a significant gap in samples.
private static final long MAX_FILTER_DELTA_TIME_NANOS = 1000 * NANOS_PER_MS;
// The acceleration filter time constant.
//
// This time constant is used to tune the acceleration filter such that
// impulses and vibrational noise (think car dock) is suppressed before we
// try to calculate the tilt and orientation angles.
//
// The filter time constant is related to the filter cutoff frequency, which is the
// frequency at which signals are attenuated by 3dB (half the passband power).
// Each successive octave beyond this frequency is attenuated by an additional 6dB.
//
// Given a time constant t in seconds, the filter cutoff frequency Fc in Hertz
// is given by Fc = 1 / (2pi * t).
//
// The higher the time constant, the lower the cutoff frequency, so more noise
// will be suppressed.
//
// Filtering adds latency proportional the time constant (inversely proportional
// to the cutoff frequency) so we don't want to make the time constant too
// large or we can lose responsiveness. Likewise we don't want to make it too
// small or we do a poor job suppressing acceleration spikes.
// Empirically, 100ms seems to be too small and 500ms is too large.
private static final float FILTER_TIME_CONSTANT_MS = 200.0f;
/* State for orientation detection. */
// Thresholds for minimum and maximum allowable deviation from gravity.
//
// If the device is undergoing external acceleration (being bumped, in a car
// that is turning around a corner or a plane taking off) then the magnitude
// may be substantially more or less than gravity. This can skew our orientation
// detection by making us think that up is pointed in a different direction.
//
// Conversely, if the device is in freefall, then there will be no gravity to
// measure at all. This is problematic because we cannot detect the orientation
// without gravity to tell us which way is up. A magnitude near 0 produces
// singularities in the tilt and orientation calculations.
//
// In both cases, we postpone choosing an orientation.
//
// However, we need to tolerate some acceleration because the angular momentum
// of turning the device can skew the observed acceleration for a short period of time.
private static final float NEAR_ZERO_MAGNITUDE = 1; // m/s^2
private static final float ACCELERATION_TOLERANCE = 4; // m/s^2
private static final float MIN_ACCELERATION_MAGNITUDE =
SensorManager.STANDARD_GRAVITY - ACCELERATION_TOLERANCE;
private static final float MAX_ACCELERATION_MAGNITUDE =
SensorManager.STANDARD_GRAVITY + ACCELERATION_TOLERANCE;
// 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;
// The tilt angle range in degrees for each orientation.
// Beyond these tilt angles, we don't even consider transitioning into the
// specified orientation. We place more stringent requirements on unnatural
// orientations than natural ones to make it less likely to accidentally transition
// into those states.
// The first value of each pair is negative so it applies a limit when the device is
// facing down (overhead reading in bed).
// The second value of each pair is positive so it applies a limit when the device is
// facing up (resting on a table).
// The ideal tilt angle is 0 (when the device is vertical) so the limits establish
// how close to vertical the device must be in order to change orientation.
private static final int[][] TILT_TOLERANCE = new int[][] {
/* ROTATION_0 */ { -25, 70 },
/* ROTATION_90 */ { -25, 65 },
/* ROTATION_180 */ { -25, 60 },
/* ROTATION_270 */ { -25, 65 }
};
// The gap angle in degrees between adjacent orientation angles for hysteresis.
// This creates a "dead zone" between the current orientation and a proposed
// adjacent orientation. No orientation proposal is made when the orientation
// angle is within the gap between the current orientation and the adjacent
// orientation.
private static final int ADJACENT_ORIENTATION_ANGLE_GAP = 45;
// Timestamp and value of the last accelerometer sample.
private long mLastFilteredTimestampNanos;
private float mLastFilteredX, mLastFilteredY, mLastFilteredZ;
// The last proposed rotation, -1 if unknown.
private int mProposedRotation;
// Value of the current predicted rotation, -1 if unknown.
private int mPredictedRotation;
// Timestamp of when the predicted rotation most recently changed.
private long mPredictedRotationTimestampNanos;
// Timestamp when the device last appeared to be flat for sure (the flat delay elapsed).
private long mFlatTimestampNanos;
// Timestamp when the device last appeared to be swinging.
private long mSwingTimestampNanos;
// Timestamp when the device last appeared to be undergoing external acceleration.
private long mAccelerationTimestampNanos;
// History of observed tilt angles.
private static final int TILT_HISTORY_SIZE = 40;
private float[] mTiltHistory = new float[TILT_HISTORY_SIZE];
private long[] mTiltHistoryTimestampNanos = new long[TILT_HISTORY_SIZE];
private int mTiltHistoryIndex;
public SensorEventListenerImpl(WindowOrientationListener orientationListener) {
mOrientationListener = orientationListener;
reset();
}
public int getProposedRotation() {
return mProposedRotation;
}
@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
}
@Override
public void onSensorChanged(SensorEvent event) {
// The vector given in the SensorEvent points straight up (towards the sky) under ideal
// conditions (the phone is not accelerating). I'll call this up vector elsewhere.
float x = event.values[ACCELEROMETER_DATA_X];
float y = event.values[ACCELEROMETER_DATA_Y];
float z = event.values[ACCELEROMETER_DATA_Z];
if (LOG) {
Slog.v(TAG, "Raw acceleration vector: "
+ "x=" + x + ", y=" + y + ", z=" + z
+ ", magnitude=" + FloatMath.sqrt(x * x + y * y + z * z));
}
// Apply a low-pass filter to the acceleration up vector in cartesian space.
// Reset the orientation listener state if the samples are too far apart in time
// or when we see values of (0, 0, 0) which indicates that we polled the
// accelerometer too soon after turning it on and we don't have any data yet.
final long now = event.timestamp;
final long then = mLastFilteredTimestampNanos;
final float timeDeltaMS = (now - then) * 0.000001f;
final boolean skipSample;
if (now < then
|| now > then + MAX_FILTER_DELTA_TIME_NANOS
|| (x == 0 && y == 0 && z == 0)) {
if (LOG) {
Slog.v(TAG, "Resetting orientation listener.");
}
reset();
skipSample = true;
} else {
final float alpha = timeDeltaMS / (FILTER_TIME_CONSTANT_MS + timeDeltaMS);
x = alpha * (x - mLastFilteredX) + mLastFilteredX;
y = alpha * (y - mLastFilteredY) + mLastFilteredY;
z = alpha * (z - mLastFilteredZ) + mLastFilteredZ;
if (LOG) {
Slog.v(TAG, "Filtered acceleration vector: "
+ "x=" + x + ", y=" + y + ", z=" + z
+ ", magnitude=" + FloatMath.sqrt(x * x + y * y + z * z));
}
skipSample = false;
}
mLastFilteredTimestampNanos = now;
mLastFilteredX = x;
mLastFilteredY = y;
mLastFilteredZ = z;
boolean isAccelerating = false;
boolean isFlat = false;
boolean isSwinging = false;
if (!skipSample) {
// Calculate the magnitude of the acceleration vector.
final float magnitude = FloatMath.sqrt(x * x + y * y + z * z);
if (magnitude < NEAR_ZERO_MAGNITUDE) {
if (LOG) {
Slog.v(TAG, "Ignoring sensor data, magnitude too close to zero.");
}
clearPredictedRotation();
} else {
// Determine whether the device appears to be undergoing external acceleration.
if (isAccelerating(magnitude)) {
isAccelerating = true;
mAccelerationTimestampNanos = now;
}
// Calculate the tilt angle.
// This is the angle between the up vector and the x-y plane (the plane of
// the screen) in a range of [-90, 90] degrees.
// -90 degrees: screen horizontal and facing the ground (overhead)
// 0 degrees: screen vertical
// 90 degrees: screen horizontal and facing the sky (on table)
final int tiltAngle = (int) Math.round(
Math.asin(z / magnitude) * RADIANS_TO_DEGREES);
addTiltHistoryEntry(now, tiltAngle);
// Determine whether the device appears to be flat or swinging.
if (isFlat(now)) {
isFlat = true;
mFlatTimestampNanos = now;
}
if (isSwinging(now, tiltAngle)) {
isSwinging = true;
mSwingTimestampNanos = now;
}
// If the tilt angle is too close to horizontal then we cannot determine
// the orientation angle of the screen.
if (Math.abs(tiltAngle) > MAX_TILT) {
if (LOG) {
Slog.v(TAG, "Ignoring sensor data, tilt angle too high: "
+ "tiltAngle=" + tiltAngle);
}
clearPredictedRotation();
} else {
// Calculate the orientation angle.
// This is the angle between the x-y projection of the up vector onto
// the +y-axis, increasing clockwise in a range of [0, 360] degrees.
int orientationAngle = (int) Math.round(
-Math.atan2(-x, y) * RADIANS_TO_DEGREES);
if (orientationAngle < 0) {
// atan2 returns [-180, 180]; normalize to [0, 360]
orientationAngle += 360;
}
// Find the nearest rotation.
int nearestRotation = (orientationAngle + 45) / 90;
if (nearestRotation == 4) {
nearestRotation = 0;
}
// Determine the predicted orientation.
if (isTiltAngleAcceptable(nearestRotation, tiltAngle)
&& isOrientationAngleAcceptable(nearestRotation,
orientationAngle)) {
updatePredictedRotation(now, nearestRotation);
if (LOG) {
Slog.v(TAG, "Predicted: "
+ "tiltAngle=" + tiltAngle
+ ", orientationAngle=" + orientationAngle
+ ", predictedRotation=" + mPredictedRotation
+ ", predictedRotationAgeMS="
+ ((now - mPredictedRotationTimestampNanos)
* 0.000001f));
}
} else {
if (LOG) {
Slog.v(TAG, "Ignoring sensor data, no predicted rotation: "
+ "tiltAngle=" + tiltAngle
+ ", orientationAngle=" + orientationAngle);
}
clearPredictedRotation();
}
}
}
}
// Determine new proposed rotation.
final int oldProposedRotation = mProposedRotation;
if (mPredictedRotation < 0 || isPredictedRotationAcceptable(now)) {
mProposedRotation = mPredictedRotation;
}
// Write final statistics about where we are in the orientation detection process.
if (LOG) {
Slog.v(TAG, "Result: currentRotation=" + mOrientationListener.mCurrentRotation
+ ", proposedRotation=" + mProposedRotation
+ ", predictedRotation=" + mPredictedRotation
+ ", timeDeltaMS=" + timeDeltaMS
+ ", isAccelerating=" + isAccelerating
+ ", isFlat=" + isFlat
+ ", isSwinging=" + isSwinging
+ ", timeUntilSettledMS=" + remainingMS(now,
mPredictedRotationTimestampNanos + PROPOSAL_SETTLE_TIME_NANOS)
+ ", timeUntilAccelerationDelayExpiredMS=" + remainingMS(now,
mAccelerationTimestampNanos + PROPOSAL_MIN_TIME_SINCE_ACCELERATION_ENDED_NANOS)
+ ", timeUntilFlatDelayExpiredMS=" + remainingMS(now,
mFlatTimestampNanos + PROPOSAL_MIN_TIME_SINCE_FLAT_ENDED_NANOS)
+ ", timeUntilSwingDelayExpiredMS=" + remainingMS(now,
mSwingTimestampNanos + PROPOSAL_MIN_TIME_SINCE_SWING_ENDED_NANOS));
}
// Tell the listener.
if (mProposedRotation != oldProposedRotation && mProposedRotation >= 0) {
if (LOG) {
Slog.v(TAG, "Proposed rotation changed! proposedRotation=" + mProposedRotation
+ ", oldProposedRotation=" + oldProposedRotation);
}
mOrientationListener.onProposedRotationChanged(mProposedRotation);
}
}
/**
* Returns true if the tilt angle is acceptable for a given predicted rotation.
*/
private boolean isTiltAngleAcceptable(int rotation, int tiltAngle) {
return tiltAngle >= TILT_TOLERANCE[rotation][0]
&& tiltAngle <= TILT_TOLERANCE[rotation][1];
}
/**
* Returns true if the orientation angle is acceptable for a given predicted rotation.
*
* This function takes into account the gap between adjacent orientations
* for hysteresis.
*/
private boolean isOrientationAngleAcceptable(int rotation, int orientationAngle) {
// If there is no current rotation, then there is no gap.
// The gap is used only to introduce hysteresis among advertised orientation
// changes to avoid flapping.
final int currentRotation = mOrientationListener.mCurrentRotation;
if (currentRotation >= 0) {
// If the specified rotation is the same or is counter-clockwise adjacent
// to the current rotation, then we set a lower bound on the orientation angle.
// For example, if currentRotation is ROTATION_0 and proposed is ROTATION_90,
// then we want to check orientationAngle > 45 + GAP / 2.
if (rotation == currentRotation
|| rotation == (currentRotation + 1) % 4) {
int lowerBound = rotation * 90 - 45
+ ADJACENT_ORIENTATION_ANGLE_GAP / 2;
if (rotation == 0) {
if (orientationAngle >= 315 && orientationAngle < lowerBound + 360) {
return false;
}
} else {
if (orientationAngle < lowerBound) {
return false;
}
}
}
// If the specified rotation is the same or is clockwise adjacent,
// then we set an upper bound on the orientation angle.
// For example, if currentRotation is ROTATION_0 and rotation is ROTATION_270,
// then we want to check orientationAngle < 315 - GAP / 2.
if (rotation == currentRotation
|| rotation == (currentRotation + 3) % 4) {
int upperBound = rotation * 90 + 45
- ADJACENT_ORIENTATION_ANGLE_GAP / 2;
if (rotation == 0) {
if (orientationAngle <= 45 && orientationAngle > upperBound) {
return false;
}
} else {
if (orientationAngle > upperBound) {
return false;
}
}
}
}
return true;
}
/**
* Returns true if the predicted rotation is ready to be advertised as a
* proposed rotation.
*/
private boolean isPredictedRotationAcceptable(long now) {
// The predicted rotation must have settled long enough.
if (now < mPredictedRotationTimestampNanos + PROPOSAL_SETTLE_TIME_NANOS) {
return false;
}
// The last flat state (time since picked up) must have been sufficiently long ago.
if (now < mFlatTimestampNanos + PROPOSAL_MIN_TIME_SINCE_FLAT_ENDED_NANOS) {
return false;
}
// The last swing state (time since last movement to put down) must have been
// sufficiently long ago.
if (now < mSwingTimestampNanos + PROPOSAL_MIN_TIME_SINCE_SWING_ENDED_NANOS) {
return false;
}
// The last acceleration state must have been sufficiently long ago.
if (now < mAccelerationTimestampNanos
+ PROPOSAL_MIN_TIME_SINCE_ACCELERATION_ENDED_NANOS) {
return false;
}
// Looks good!
return true;
}
private void reset() {
mLastFilteredTimestampNanos = Long.MIN_VALUE;
mProposedRotation = -1;
mFlatTimestampNanos = Long.MIN_VALUE;
mSwingTimestampNanos = Long.MIN_VALUE;
mAccelerationTimestampNanos = Long.MIN_VALUE;
clearPredictedRotation();
clearTiltHistory();
}
private void clearPredictedRotation() {
mPredictedRotation = -1;
mPredictedRotationTimestampNanos = Long.MIN_VALUE;
}
private void updatePredictedRotation(long now, int rotation) {
if (mPredictedRotation != rotation) {
mPredictedRotation = rotation;
mPredictedRotationTimestampNanos = now;
}
}
private boolean isAccelerating(float magnitude) {
return magnitude < MIN_ACCELERATION_MAGNITUDE
|| magnitude > MAX_ACCELERATION_MAGNITUDE;
}
private void clearTiltHistory() {
mTiltHistoryTimestampNanos[0] = Long.MIN_VALUE;
mTiltHistoryIndex = 1;
}
private void addTiltHistoryEntry(long now, float tilt) {
mTiltHistory[mTiltHistoryIndex] = tilt;
mTiltHistoryTimestampNanos[mTiltHistoryIndex] = now;
mTiltHistoryIndex = (mTiltHistoryIndex + 1) % TILT_HISTORY_SIZE;
mTiltHistoryTimestampNanos[mTiltHistoryIndex] = Long.MIN_VALUE;
}
private boolean isFlat(long now) {
for (int i = mTiltHistoryIndex; (i = nextTiltHistoryIndex(i)) >= 0; ) {
if (mTiltHistory[i] < FLAT_ANGLE) {
break;
}
if (mTiltHistoryTimestampNanos[i] + FLAT_TIME_NANOS <= now) {
// Tilt has remained greater than FLAT_TILT_ANGLE for FLAT_TIME_NANOS.
return true;
}
}
return false;
}
private boolean isSwinging(long now, float tilt) {
for (int i = mTiltHistoryIndex; (i = nextTiltHistoryIndex(i)) >= 0; ) {
if (mTiltHistoryTimestampNanos[i] + SWING_TIME_NANOS < now) {
break;
}
if (mTiltHistory[i] + SWING_AWAY_ANGLE_DELTA <= tilt) {
// Tilted away by SWING_AWAY_ANGLE_DELTA within SWING_TIME_NANOS.
return true;
}
}
return false;
}
private int nextTiltHistoryIndex(int index) {
index = (index == 0 ? TILT_HISTORY_SIZE : index) - 1;
return mTiltHistoryTimestampNanos[index] != Long.MIN_VALUE ? index : -1;
}
private static float remainingMS(long now, long until) {
return now >= until ? 0 : (until - now) * 0.000001f;
}
}
}