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      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 
     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 }