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      1 /*
      2  * Copyright (C) 2016 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.incallui.answer.impl.classifier;
     18 
     19 import android.util.ArrayMap;
     20 import android.view.MotionEvent;
     21 import java.util.Map;
     22 
     23 /**
     24  * A classifier which looks at the speed and distance between successive points of a Stroke. It
     25  * looks at two consecutive speeds between two points and calculates the ratio between them. The
     26  * final result is the maximum of these values. It does the same for distances. If some speed or
     27  * distance is equal to zero then the ratio between this and the next part is not calculated. To the
     28  * duration of each part there is added one nanosecond so that it is always possible to calculate
     29  * the speed of a part.
     30  */
     31 class AccelerationClassifier extends StrokeClassifier {
     32   private final Map<Stroke, Data> mStrokeMap = new ArrayMap<>();
     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(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 }
    100