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/*
* Copyright (C) 2016 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License
*/
package com.android.incallui.answer.impl.classifier;
import android.util.ArrayMap;
import android.view.MotionEvent;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
/**
* A classifier which calculates the variance of differences between successive angles in a stroke.
* For each stroke it keeps its last three points. If some successive points are the same, it
* ignores the repetitions. If a new point is added, the classifier calculates the angle between the
* last three points. After that, it calculates the difference between this angle and the previously
* calculated angle. Then it calculates the variance of the differences from a stroke. To the
* differences there is artificially added value 0.0 and the difference between the first angle and
* PI (angles are in radians). It helps with strokes which have few points and punishes more strokes
* which are not smooth.
*
* <p>This classifier also tries to split the stroke into two parts in the place in which the
* biggest angle is. It calculates the angle variance of the two parts and sums them up. The reason
* the classifier is doing this, is because some human swipes at the beginning go for a moment in
* one direction and then they rapidly change direction for the rest of the stroke (like a tick).
* The final result is the minimum of angle variance of the whole stroke and the sum of angle
* variances of the two parts split up. The classifier tries the tick option only if the first part
* is shorter than the second part.
*
* <p>Additionally, the classifier classifies the angles as left angles (those angles which value is
* in [0.0, PI - ANGLE_DEVIATION) interval), straight angles ([PI - ANGLE_DEVIATION, PI +
* ANGLE_DEVIATION] interval) and right angles ((PI + ANGLE_DEVIATION, 2 * PI) interval) and then
* calculates the percentage of angles which are in the same direction (straight angles can be left
* angels or right angles)
*/
class AnglesClassifier extends StrokeClassifier {
private Map<Stroke, Data> strokeMap = new ArrayMap<>();
public AnglesClassifier(ClassifierData classifierData) {
this.classifierData = classifierData;
}
@Override
public String getTag() {
return "ANG";
}
@Override
public void onTouchEvent(MotionEvent event) {
int action = event.getActionMasked();
if (action == MotionEvent.ACTION_DOWN) {
strokeMap.clear();
}
for (int i = 0; i < event.getPointerCount(); i++) {
Stroke stroke = classifierData.getStroke(event.getPointerId(i));
if (strokeMap.get(stroke) == null) {
strokeMap.put(stroke, new Data());
}
strokeMap.get(stroke).addPoint(stroke.getPoints().get(stroke.getPoints().size() - 1));
}
}
@Override
public float getFalseTouchEvaluation(Stroke stroke) {
Data data = strokeMap.get(stroke);
return AnglesVarianceEvaluator.evaluate(data.getAnglesVariance())
+ AnglesPercentageEvaluator.evaluate(data.getAnglesPercentage());
}
private static class Data {
private static final float ANGLE_DEVIATION = (float) Math.PI / 20.0f;
private static final float MIN_MOVE_DIST_DP = .01f;
private List<Point> lastThreePoints = new ArrayList<>();
private float firstAngleVariance;
private float previousAngle;
private float biggestAngle;
private float sumSquares;
private float secondSumSquares;
private float sum;
private float secondSum;
private float count;
private float secondCount;
private float firstLength;
private float length;
private float anglesCount;
private float leftAngles;
private float rightAngles;
private float straightAngles;
public Data() {
firstAngleVariance = 0.0f;
previousAngle = (float) Math.PI;
biggestAngle = 0.0f;
sumSquares = secondSumSquares = 0.0f;
sum = secondSum = 0.0f;
count = secondCount = 1.0f;
length = firstLength = 0.0f;
anglesCount = leftAngles = rightAngles = straightAngles = 0.0f;
}
public void addPoint(Point point) {
// Checking if the added point is different than the previously added point
// Repetitions and short distances are being ignored so that proper angles are calculated.
if (lastThreePoints.isEmpty()
|| (!lastThreePoints.get(lastThreePoints.size() - 1).equals(point)
&& (lastThreePoints.get(lastThreePoints.size() - 1).dist(point)
> MIN_MOVE_DIST_DP))) {
if (!lastThreePoints.isEmpty()) {
length += lastThreePoints.get(lastThreePoints.size() - 1).dist(point);
}
lastThreePoints.add(point);
if (lastThreePoints.size() == 4) {
lastThreePoints.remove(0);
float angle =
lastThreePoints.get(1).getAngle(lastThreePoints.get(0), lastThreePoints.get(2));
anglesCount++;
if (angle < Math.PI - ANGLE_DEVIATION) {
leftAngles++;
} else if (angle <= Math.PI + ANGLE_DEVIATION) {
straightAngles++;
} else {
rightAngles++;
}
float difference = angle - previousAngle;
// If this is the biggest angle of the stroke so then we save the value of
// the angle variance so far and start to count the values for the angle
// variance of the second part.
if (biggestAngle < angle) {
biggestAngle = angle;
firstLength = length;
firstAngleVariance = getAnglesVariance(sumSquares, sum, count);
secondSumSquares = 0.0f;
secondSum = 0.0f;
secondCount = 1.0f;
} else {
secondSum += difference;
secondSumSquares += difference * difference;
secondCount += 1.0f;
}
sum += difference;
sumSquares += difference * difference;
count += 1.0f;
previousAngle = angle;
}
}
}
public float getAnglesVariance(float sumSquares, float sum, float count) {
return sumSquares / count - (sum / count) * (sum / count);
}
public float getAnglesVariance() {
float anglesVariance = getAnglesVariance(sumSquares, sum, count);
if (firstLength < length / 2f) {
anglesVariance =
Math.min(
anglesVariance,
firstAngleVariance + getAnglesVariance(secondSumSquares, secondSum, secondCount));
}
return anglesVariance;
}
public float getAnglesPercentage() {
if (anglesCount == 0.0f) {
return 1.0f;
}
return (Math.max(leftAngles, rightAngles) + straightAngles) / anglesCount;
}
}
}
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