/*
* Copyright (C) 2006 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.annotation.IntDef;
import android.compat.annotation.UnsupportedAppUsage;
import android.hardware.input.InputManagerGlobal;
import android.util.ArrayMap;
import android.util.Pools.SynchronizedPool;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.Map;
/**
* Helper for tracking the velocity of motion events, for implementing
* flinging and other such gestures.
*
* Use {@link #obtain} to retrieve a new instance of the class when you are going
* to begin tracking. Put the motion events you receive into it with
* {@link #addMovement(MotionEvent)}. When you want to determine the velocity, call
* {@link #computeCurrentVelocity(int)} and then call the velocity-getter methods like
* {@link #getXVelocity(int)}, {@link #getYVelocity(int)}, or {@link #getAxisVelocity(int, int)}
* to retrieve velocity for different axes and/or pointer IDs.
*/
public final class VelocityTracker {
private static final SynchronizedPool<VelocityTracker> sPool =
new SynchronizedPool<VelocityTracker>(2);
private static final int ACTIVE_POINTER_ID = -1;
/** @hide */
@IntDef(value = {
MotionEvent.AXIS_X,
MotionEvent.AXIS_Y,
MotionEvent.AXIS_SCROLL
})
@Retention(RetentionPolicy.SOURCE)
public @interface VelocityTrackableMotionEventAxis {}
/**
* Velocity Tracker Strategy: Invalid.
*
* @hide
*/
public static final int VELOCITY_TRACKER_STRATEGY_DEFAULT = -1;
/**
* Velocity Tracker Strategy: Impulse.
* Physical model of pushing an object. Quality: VERY GOOD.
* Works with duplicate coordinates, unclean finger liftoff.
*
* @hide
*/
public static final int VELOCITY_TRACKER_STRATEGY_IMPULSE = 0;
/**
* Velocity Tracker Strategy: LSQ1.
* 1st order least squares. Quality: POOR.
* Frequently underfits the touch data especially when the finger accelerates
* or changes direction. Often underestimates velocity. The direction
* is overly influenced by historical touch points.
*
* @hide
*/
public static final int VELOCITY_TRACKER_STRATEGY_LSQ1 = 1;
/**
* Velocity Tracker Strategy: LSQ2.
* 2nd order least squares. Quality: VERY GOOD.
* Pretty much ideal, but can be confused by certain kinds of touch data,
* particularly if the panel has a tendency to generate delayed,
* duplicate or jittery touch coordinates when the finger is released.
*
* @hide
*/
public static final int VELOCITY_TRACKER_STRATEGY_LSQ2 = 2;
/**
* Velocity Tracker Strategy: LSQ3.
* 3rd order least squares. Quality: UNUSABLE.
* Frequently overfits the touch data yielding wildly divergent estimates
* of the velocity when the finger is released.
*
* @hide
*/
public static final int VELOCITY_TRACKER_STRATEGY_LSQ3 = 3;
/**
* Velocity Tracker Strategy: WLSQ2_DELTA.
* 2nd order weighted least squares, delta weighting. Quality: EXPERIMENTAL
*
* @hide
*/
public static final int VELOCITY_TRACKER_STRATEGY_WLSQ2_DELTA = 4;
/**
* Velocity Tracker Strategy: WLSQ2_CENTRAL.
* 2nd order weighted least squares, central weighting. Quality: EXPERIMENTAL
*
* @hide
*/
public static final int VELOCITY_TRACKER_STRATEGY_WLSQ2_CENTRAL = 5;
/**
* Velocity Tracker Strategy: WLSQ2_RECENT.
* 2nd order weighted least squares, recent weighting. Quality: EXPERIMENTAL
*
* @hide
*/
public static final int VELOCITY_TRACKER_STRATEGY_WLSQ2_RECENT = 6;
/**
* Velocity Tracker Strategy: INT1.
* 1st order integrating filter. Quality: GOOD.
* Not as good as 'lsq2' because it cannot estimate acceleration but it is
* more tolerant of errors. Like 'lsq1', this strategy tends to underestimate
* the velocity of a fling but this strategy tends to respond to changes in
* direction more quickly and accurately.
*
* @hide
*/
public static final int VELOCITY_TRACKER_STRATEGY_INT1 = 7;
/**
* Velocity Tracker Strategy: INT2.
* 2nd order integrating filter. Quality: EXPERIMENTAL.
* For comparison purposes only. Unlike 'int1' this strategy can compensate
* for acceleration but it typically overestimates the effect.
*
* @hide
*/
public static final int VELOCITY_TRACKER_STRATEGY_INT2 = 8;
/**
* Velocity Tracker Strategy: Legacy.
* Legacy velocity tracker algorithm. Quality: POOR.
* For comparison purposes only. This algorithm is strongly influenced by
* old data points, consistently underestimates velocity and takes a very long
* time to adjust to changes in direction.
*
* @hide
*/
public static final int VELOCITY_TRACKER_STRATEGY_LEGACY = 9;
/**
* Velocity Tracker Strategy look up table.
*/
private static final Map<String, Integer> STRATEGIES = new ArrayMap<>();
/** @hide */
@Retention(RetentionPolicy.SOURCE)
@IntDef(prefix = {"VELOCITY_TRACKER_STRATEGY_"}, value = {
VELOCITY_TRACKER_STRATEGY_DEFAULT,
VELOCITY_TRACKER_STRATEGY_IMPULSE,
VELOCITY_TRACKER_STRATEGY_LSQ1,
VELOCITY_TRACKER_STRATEGY_LSQ2,
VELOCITY_TRACKER_STRATEGY_LSQ3,
VELOCITY_TRACKER_STRATEGY_WLSQ2_DELTA,
VELOCITY_TRACKER_STRATEGY_WLSQ2_CENTRAL,
VELOCITY_TRACKER_STRATEGY_WLSQ2_RECENT,
VELOCITY_TRACKER_STRATEGY_INT1,
VELOCITY_TRACKER_STRATEGY_INT2,
VELOCITY_TRACKER_STRATEGY_LEGACY
})
public @interface VelocityTrackerStrategy {}
private long mPtr;
@VelocityTrackerStrategy
private final int mStrategy;
private static native long nativeInitialize(int strategy);
private static native void nativeDispose(long ptr);
private static native void nativeClear(long ptr);
private static native void nativeAddMovement(long ptr, MotionEvent event);
private static native void nativeComputeCurrentVelocity(long ptr, int units, float maxVelocity);
private static native float nativeGetVelocity(long ptr, int axis, int id);
private static native boolean nativeIsAxisSupported(int axis);
static {
// Strategy string and IDs mapping lookup.
STRATEGIES.put("impulse", VELOCITY_TRACKER_STRATEGY_IMPULSE);
STRATEGIES.put("lsq1", VELOCITY_TRACKER_STRATEGY_LSQ1);
STRATEGIES.put("lsq2", VELOCITY_TRACKER_STRATEGY_LSQ2);
STRATEGIES.put("lsq3", VELOCITY_TRACKER_STRATEGY_LSQ3);
STRATEGIES.put("wlsq2-delta", VELOCITY_TRACKER_STRATEGY_WLSQ2_DELTA);
STRATEGIES.put("wlsq2-central", VELOCITY_TRACKER_STRATEGY_WLSQ2_CENTRAL);
STRATEGIES.put("wlsq2-recent", VELOCITY_TRACKER_STRATEGY_WLSQ2_RECENT);
STRATEGIES.put("int1", VELOCITY_TRACKER_STRATEGY_INT1);
STRATEGIES.put("int2", VELOCITY_TRACKER_STRATEGY_INT2);
STRATEGIES.put("legacy", VELOCITY_TRACKER_STRATEGY_LEGACY);
}
/**
* Return a strategy ID from string.
*/
private static int toStrategyId(String strStrategy) {
if (STRATEGIES.containsKey(strStrategy)) {
return STRATEGIES.get(strStrategy);
}
return VELOCITY_TRACKER_STRATEGY_DEFAULT;
}
/**
* Retrieve a new VelocityTracker object to watch the velocity of a
* motion. Be sure to call {@link #recycle} when done. You should
* generally only maintain an active object while tracking a movement,
* so that the VelocityTracker can be re-used elsewhere.
*
* @return Returns a new VelocityTracker.
*/
static public VelocityTracker obtain() {
VelocityTracker instance = sPool.acquire();
return (instance != null) ? instance
: new VelocityTracker(VELOCITY_TRACKER_STRATEGY_DEFAULT);
}
/**
* Obtains a velocity tracker with the specified strategy as string.
* For testing and comparison purposes only.
* @deprecated Use {@link obtain(int strategy)} instead.
*
* @param strategy The strategy, or null to use the default.
* @return The velocity tracker.
*
* @hide
*/
@UnsupportedAppUsage
@Deprecated
public static VelocityTracker obtain(String strategy) {
if (strategy == null) {
return obtain();
}
return new VelocityTracker(toStrategyId(strategy));
}
/**
* Obtains a velocity tracker with the specified strategy.
* For testing and comparison purposes only.
*
* @param strategy The strategy Id, VELOCITY_TRACKER_STRATEGY_DEFAULT to use the default.
* @return The velocity tracker.
*
* @hide
*/
public static VelocityTracker obtain(int strategy) {
return new VelocityTracker(strategy);
}
/**
* Return a VelocityTracker object back to be re-used by others. You must
* not touch the object after calling this function.
*/
public void recycle() {
if (mStrategy == VELOCITY_TRACKER_STRATEGY_DEFAULT) {
clear();
sPool.release(this);
}
}
/**
* Return strategy Id of VelocityTracker object.
* @return The velocity tracker strategy Id.
*
* @hide
*/
public int getStrategyId() {
return mStrategy;
}
private VelocityTracker(@VelocityTrackerStrategy int strategy) {
// If user has not selected a specific strategy
if (strategy == VELOCITY_TRACKER_STRATEGY_DEFAULT) {
final String strategyProperty = InputManagerGlobal.getInstance()
.getVelocityTrackerStrategy();
// Check if user specified strategy by overriding system property.
if (strategyProperty == null || strategyProperty.isEmpty()) {
mStrategy = strategy;
} else {
mStrategy = toStrategyId(strategyProperty);
}
} else {
// User specified strategy
mStrategy = strategy;
}
mPtr = nativeInitialize(mStrategy);
}
@Override
protected void finalize() throws Throwable {
try {
if (mPtr != 0) {
nativeDispose(mPtr);
mPtr = 0;
}
} finally {
super.finalize();
}
}
/**
* Checks whether a given velocity-trackable {@link MotionEvent} axis is supported for velocity
* tracking by this {@link VelocityTracker} instance (refer to
* {@link #getAxisVelocity(int, int)} for a list of potentially velocity-trackable axes).
*
* <p>Note that the value returned from this method will stay the same for a given instance, so
* a single check for axis support is enough per a {@link VelocityTracker} instance.
*
* @param axis The axis to check for velocity support.
* @return {@code true} if {@code axis} is supported for velocity tracking, or {@code false}
* otherwise.
* @see #getAxisVelocity(int, int)
* @see #getAxisVelocity(int)
*/
public boolean isAxisSupported(@VelocityTrackableMotionEventAxis int axis) {
return nativeIsAxisSupported(axis);
}
/**
* Reset the velocity tracker back to its initial state.
*/
public void clear() {
nativeClear(mPtr);
}
/**
* Add a user's movement to the tracker. You should call this for the
* initial {@link MotionEvent#ACTION_DOWN}, the following
* {@link MotionEvent#ACTION_MOVE} events that you receive, and the
* final {@link MotionEvent#ACTION_UP}. You can, however, call this
* for whichever events you desire.
*
* @param event The MotionEvent you received and would like to track.
*/
public void addMovement(MotionEvent event) {
if (event == null) {
throw new IllegalArgumentException("event must not be null");
}
nativeAddMovement(mPtr, event);
}
/**
* Equivalent to invoking {@link #computeCurrentVelocity(int, float)} with a maximum
* velocity of Float.MAX_VALUE.
*
* @see #computeCurrentVelocity(int, float)
*/
public void computeCurrentVelocity(int units) {
nativeComputeCurrentVelocity(mPtr, units, Float.MAX_VALUE);
}
/**
* Compute the current velocity based on the points that have been
* collected. Only call this when you actually want to retrieve velocity
* information, as it is relatively expensive. You can then retrieve
* the velocity with {@link #getXVelocity()} and
* {@link #getYVelocity()}.
*
* @param units The units you would like the velocity in. A value of 1
* provides units per millisecond, 1000 provides units per second, etc.
* Note that the units referred to here are the same units with which motion is reported. For
* axes X and Y, the units are pixels.
* @param maxVelocity The maximum velocity that can be computed by this method.
* This value must be declared in the same unit as the units parameter. This value
* must be positive.
*/
public void computeCurrentVelocity(int units, float maxVelocity) {
nativeComputeCurrentVelocity(mPtr, units, maxVelocity);
}
/**
* Retrieve the last computed X velocity. You must first call
* {@link #computeCurrentVelocity(int)} before calling this function.
*
* @return The previously computed X velocity.
*/
public float getXVelocity() {
return getXVelocity(ACTIVE_POINTER_ID);
}
/**
* Retrieve the last computed Y velocity. You must first call
* {@link #computeCurrentVelocity(int)} before calling this function.
*
* @return The previously computed Y velocity.
*/
public float getYVelocity() {
return getYVelocity(ACTIVE_POINTER_ID);
}
/**
* Retrieve the last computed X velocity. You must first call
* {@link #computeCurrentVelocity(int)} before calling this function.
*
* @param id Which pointer's velocity to return.
* @return The previously computed X velocity.
*/
public float getXVelocity(int id) {
return nativeGetVelocity(mPtr, MotionEvent.AXIS_X, id);
}
/**
* Retrieve the last computed Y velocity. You must first call
* {@link #computeCurrentVelocity(int)} before calling this function.
*
* @param id Which pointer's velocity to return.
* @return The previously computed Y velocity.
*/
public float getYVelocity(int id) {
return nativeGetVelocity(mPtr, MotionEvent.AXIS_Y, id);
}
/**
* Retrieve the last computed velocity for a given motion axis. You must first call
* {@link #computeCurrentVelocity(int)} or {@link #computeCurrentVelocity(int, float)} before
* calling this function.
*
* <p>In addition to {@link MotionEvent#AXIS_X} and {@link MotionEvent#AXIS_Y} which have been
* supported since the introduction of this class, the following axes can be candidates for this
* method:
* <ul>
* <li> {@link MotionEvent#AXIS_SCROLL}: supported starting
* {@link android.os.Build.VERSION_CODES#UPSIDE_DOWN_CAKE}
* </ul>
*
* <p>Before accessing velocities of an axis using this method, check that your
* {@link VelocityTracker} instance supports the axis by using {@link #isAxisSupported(int)}.
*
* @param axis Which axis' velocity to return.
* @param id Which pointer's velocity to return.
* @return The previously computed velocity for {@code axis} for pointer ID of {@code id} if
* {@code axis} is supported for velocity tracking, or 0 if velocity tracking is not supported
* for the axis.
* @see #isAxisSupported(int)
*/
public float getAxisVelocity(@VelocityTrackableMotionEventAxis int axis, int id) {
return nativeGetVelocity(mPtr, axis, id);
}
/**
* Equivalent to calling {@link #getAxisVelocity(int, int)} for {@code axis} and the active
* pointer.
*
* @param axis Which axis' velocity to return.
* @return The previously computed velocity for {@code axis} for the active pointer if
* {@code axis} is supported for velocity tracking, or 0 if velocity tracking is not supported
* for the axis.
* @see #isAxisSupported(int)
* @see #getAxisVelocity(int, int)
*/
public float getAxisVelocity(@VelocityTrackableMotionEventAxis int axis) {
return nativeGetVelocity(mPtr, axis, ACTIVE_POINTER_ID);
}
}