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/*
* Copyright (C) 2014 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 com.android.systemui.statusbar.phone;
import android.util.Log;
import android.util.Pools;
import android.view.MotionEvent;
import java.util.ArrayDeque;
import java.util.Iterator;
/**
* A very simple low-pass velocity filter for motion events for noisy touch screens.
*/
public class NoisyVelocityTracker implements VelocityTrackerInterface {
private static final Pools.SynchronizedPool<NoisyVelocityTracker> sNoisyPool =
new Pools.SynchronizedPool<>(2);
private static final float DECAY = 0.75f;
private static final boolean DEBUG = false;
private final int MAX_EVENTS = 8;
private ArrayDeque<MotionEventCopy> mEventBuf = new ArrayDeque<MotionEventCopy>(MAX_EVENTS);
private float mVX, mVY = 0;
private static class MotionEventCopy {
public MotionEventCopy(float x2, float y2, long eventTime) {
this.x = x2;
this.y = y2;
this.t = eventTime;
}
float x, y;
long t;
}
public static NoisyVelocityTracker obtain() {
NoisyVelocityTracker instance = sNoisyPool.acquire();
return (instance != null) ? instance : new NoisyVelocityTracker();
}
private NoisyVelocityTracker() {
}
public void addMovement(MotionEvent event) {
if (mEventBuf.size() == MAX_EVENTS) {
mEventBuf.remove();
}
mEventBuf.add(new MotionEventCopy(event.getX(), event.getY(), event.getEventTime()));
}
public void computeCurrentVelocity(int units) {
if (NoisyVelocityTracker.DEBUG) {
Log.v("FlingTracker", "computing velocities for " + mEventBuf.size() + " events");
}
mVX = mVY = 0;
MotionEventCopy last = null;
int i = 0;
float totalweight = 0f;
float weight = 10f;
for (final Iterator<MotionEventCopy> iter = mEventBuf.iterator();
iter.hasNext();) {
final MotionEventCopy event = iter.next();
if (last != null) {
final float dt = (float) (event.t - last.t) / units;
final float dx = (event.x - last.x);
final float dy = (event.y - last.y);
if (NoisyVelocityTracker.DEBUG) {
Log.v("FlingTracker", String.format(
" [%d] (t=%d %.1f,%.1f) dx=%.1f dy=%.1f dt=%f vx=%.1f vy=%.1f",
i, event.t, event.x, event.y,
dx, dy, dt,
(dx/dt),
(dy/dt)
));
}
if (event.t == last.t) {
// Really not sure what to do with events that happened at the same time,
// so we'll skip subsequent events.
continue;
}
mVX += weight * dx / dt;
mVY += weight * dy / dt;
totalweight += weight;
weight *= DECAY;
}
last = event;
i++;
}
if (totalweight > 0) {
mVX /= totalweight;
mVY /= totalweight;
} else {
// so as not to contaminate the velocities with NaN
mVX = mVY = 0;
}
if (NoisyVelocityTracker.DEBUG) {
Log.v("FlingTracker", "computed: vx=" + mVX + " vy=" + mVY);
}
}
public float getXVelocity() {
if (Float.isNaN(mVX) || Float.isInfinite(mVX)) {
mVX = 0;
}
return mVX;
}
public float getYVelocity() {
if (Float.isNaN(mVY) || Float.isInfinite(mVX)) {
mVY = 0;
}
return mVY;
}
public void recycle() {
mEventBuf.clear();
sNoisyPool.release(this);
}
}
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