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 
17 package com.android.systemui.classifier;
18 
19 import android.view.MotionEvent;
20 
21 import 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  */
31 public class AccelerationClassifier extends StrokeClassifier {
32     private final HashMap<Stroke, Data> mStrokeMap = new HashMap<>();
33 
AccelerationClassifier(ClassifierData classifierData)34     public AccelerationClassifier(ClassifierData classifierData) {
35         mClassifierData = classifierData;
36     }
37 
38     @Override
getTag()39     public String getTag() {
40         return "ACC";
41     }
42 
43     @Override
onTouchEvent(MotionEvent event)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
getFalseTouchEvaluation(int type, Stroke stroke)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 
Data(Point point)76         public Data(Point point) {
77             previousPoint = point;
78         }
79 
addPoint(Point point)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 }