/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License
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*/
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package com.android.systemui.classifier;
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import android.view.MotionEvent;
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import java.util.HashMap;
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/**
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* A classifier which looks at the speed and distance between successive points of a Stroke.
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* It looks at two consecutive speeds between two points and calculates the ratio between them.
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* The final result is the maximum of these values. It does the same for distances. If some speed
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* or distance is equal to zero then the ratio between this and the next part is not calculated. To
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* the duration of each part there is added one nanosecond so that it is always possible to
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* calculate the speed of a part.
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*/
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public class AccelerationClassifier extends StrokeClassifier {
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private final HashMap<Stroke, Data> mStrokeMap = new HashMap<>();
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public AccelerationClassifier(ClassifierData classifierData) {
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mClassifierData = classifierData;
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}
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@Override
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public String getTag() {
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return "ACC";
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}
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@Override
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public void onTouchEvent(MotionEvent event) {
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int action = event.getActionMasked();
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if (action == MotionEvent.ACTION_DOWN) {
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mStrokeMap.clear();
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}
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for (int i = 0; i < event.getPointerCount(); i++) {
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Stroke stroke = mClassifierData.getStroke(event.getPointerId(i));
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Point point = stroke.getPoints().get(stroke.getPoints().size() - 1);
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if (mStrokeMap.get(stroke) == null) {
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mStrokeMap.put(stroke, new Data(point));
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} else {
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mStrokeMap.get(stroke).addPoint(point);
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}
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}
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}
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@Override
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public float getFalseTouchEvaluation(int type, Stroke stroke) {
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Data data = mStrokeMap.get(stroke);
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return 2 * SpeedRatioEvaluator.evaluate(data.maxSpeedRatio);
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}
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private static class Data {
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static final float MILLIS_TO_NANOS = 1e6f;
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Point previousPoint;
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float previousSpeed = 0;
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float maxSpeedRatio = 0;
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public Data(Point point) {
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previousPoint = point;
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}
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public void addPoint(Point point) {
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float distance = previousPoint.dist(point);
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float duration = (float) (point.timeOffsetNano - previousPoint.timeOffsetNano + 1);
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float speed = distance / duration;
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if (duration > 20 * MILLIS_TO_NANOS || duration < 5 * MILLIS_TO_NANOS) {
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// reject this segment and ensure we won't use data about it in the next round.
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previousSpeed = 0;
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previousPoint = point;
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return;
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}
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if (previousSpeed != 0.0f) {
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maxSpeedRatio = Math.max(maxSpeedRatio, speed / previousSpeed);
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}
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previousSpeed = speed;
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previousPoint = point;
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}
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}
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}
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