1/*
2 * Copyright (C) 2015 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License
15 */
16
17package com.android.systemui.classifier;
18
19import android.view.MotionEvent;
20
21import java.util.HashMap;
22
23/**
24 * A classifier which looks at the speed and distance between successive points of a Stroke.
25 * It looks at two consecutive speeds between two points and calculates the ratio between them.
26 * The final result is the maximum of these values. It does the same for distances. If some speed
27 * or distance is equal to zero then the ratio between this and the next part is not calculated. To
28 * the duration of each part there is added one nanosecond so that it is always possible to
29 * calculate the speed of a part.
30 */
31public class AccelerationClassifier extends StrokeClassifier {
32    private final HashMap<Stroke, Data> mStrokeMap = new HashMap<>();
33
34    public AccelerationClassifier(ClassifierData classifierData) {
35        mClassifierData = classifierData;
36    }
37
38    @Override
39    public String getTag() {
40        return "ACC";
41    }
42
43    @Override
44    public void onTouchEvent(MotionEvent event) {
45        int action = event.getActionMasked();
46
47        if (action == MotionEvent.ACTION_DOWN) {
48            mStrokeMap.clear();
49        }
50
51        for (int i = 0; i < event.getPointerCount(); i++) {
52            Stroke stroke = mClassifierData.getStroke(event.getPointerId(i));
53            Point point = stroke.getPoints().get(stroke.getPoints().size() - 1);
54            if (mStrokeMap.get(stroke) == null) {
55                mStrokeMap.put(stroke, new Data(point));
56            } else {
57                mStrokeMap.get(stroke).addPoint(point);
58            }
59        }
60    }
61
62    @Override
63    public float getFalseTouchEvaluation(int type, Stroke stroke) {
64        Data data = mStrokeMap.get(stroke);
65        return 2 * SpeedRatioEvaluator.evaluate(data.maxSpeedRatio);
66    }
67
68    private static class Data {
69
70        static final float MILLIS_TO_NANOS = 1e6f;
71
72        Point previousPoint;
73        float previousSpeed = 0;
74        float maxSpeedRatio = 0;
75
76        public Data(Point point) {
77            previousPoint = point;
78        }
79
80        public void addPoint(Point point) {
81            float distance = previousPoint.dist(point);
82            float duration = (float) (point.timeOffsetNano - previousPoint.timeOffsetNano + 1);
83            float speed = distance / duration;
84
85            if (duration > 20 * MILLIS_TO_NANOS || duration < 5 * MILLIS_TO_NANOS) {
86                // reject this segment and ensure we won't use data about it in the next round.
87                previousSpeed = 0;
88                previousPoint = point;
89                return;
90            }
91            if (previousSpeed != 0.0f) {
92                maxSpeedRatio = Math.max(maxSpeedRatio, speed / previousSpeed);
93            }
94
95            previousSpeed = speed;
96            previousPoint = point;
97        }
98    }
99}