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/*
* Copyright (C) 2010 Google Inc.
*
* 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.inputmethod.latin;
import android.view.MotionEvent;
class SwipeTracker {
private static final int NUM_PAST = 4;
private static final int LONGEST_PAST_TIME = 200;
final EventRingBuffer mBuffer = new EventRingBuffer(NUM_PAST);
private float mYVelocity;
private float mXVelocity;
public void addMovement(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
mBuffer.clear();
return;
}
long time = ev.getEventTime();
final int count = ev.getHistorySize();
for (int i = 0; i < count; i++) {
addPoint(ev.getHistoricalX(i), ev.getHistoricalY(i), ev.getHistoricalEventTime(i));
}
addPoint(ev.getX(), ev.getY(), time);
}
private void addPoint(float x, float y, long time) {
final EventRingBuffer buffer = mBuffer;
while (buffer.size() > 0) {
long lastT = buffer.getTime(0);
if (lastT >= time - LONGEST_PAST_TIME)
break;
buffer.dropOldest();
}
buffer.add(x, y, time);
}
public void computeCurrentVelocity(int units) {
computeCurrentVelocity(units, Float.MAX_VALUE);
}
public void computeCurrentVelocity(int units, float maxVelocity) {
final EventRingBuffer buffer = mBuffer;
final float oldestX = buffer.getX(0);
final float oldestY = buffer.getY(0);
final long oldestTime = buffer.getTime(0);
float accumX = 0;
float accumY = 0;
final int count = buffer.size();
for (int pos = 1; pos < count; pos++) {
final int dur = (int)(buffer.getTime(pos) - oldestTime);
if (dur == 0) continue;
float dist = buffer.getX(pos) - oldestX;
float vel = (dist / dur) * units; // pixels/frame.
if (accumX == 0) accumX = vel;
else accumX = (accumX + vel) * .5f;
dist = buffer.getY(pos) - oldestY;
vel = (dist / dur) * units; // pixels/frame.
if (accumY == 0) accumY = vel;
else accumY = (accumY + vel) * .5f;
}
mXVelocity = accumX < 0.0f ? Math.max(accumX, -maxVelocity)
: Math.min(accumX, maxVelocity);
mYVelocity = accumY < 0.0f ? Math.max(accumY, -maxVelocity)
: Math.min(accumY, maxVelocity);
}
public float getXVelocity() {
return mXVelocity;
}
public float getYVelocity() {
return mYVelocity;
}
static class EventRingBuffer {
private final int bufSize;
private final float xBuf[];
private final float yBuf[];
private final long timeBuf[];
private int top; // points new event
private int end; // points oldest event
private int count; // the number of valid data
public EventRingBuffer(int max) {
this.bufSize = max;
xBuf = new float[max];
yBuf = new float[max];
timeBuf = new long[max];
clear();
}
public void clear() {
top = end = count = 0;
}
public int size() {
return count;
}
// Position 0 points oldest event
private int index(int pos) {
return (end + pos) % bufSize;
}
private int advance(int index) {
return (index + 1) % bufSize;
}
public void add(float x, float y, long time) {
xBuf[top] = x;
yBuf[top] = y;
timeBuf[top] = time;
top = advance(top);
if (count < bufSize) {
count++;
} else {
end = advance(end);
}
}
public float getX(int pos) {
return xBuf[index(pos)];
}
public float getY(int pos) {
return yBuf[index(pos)];
}
public long getTime(int pos) {
return timeBuf[index(pos)];
}
public void dropOldest() {
count--;
end = advance(end);
}
}
}
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