/*
* Copyright (C) 2015 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.systemui.classifier;
import android.view.MotionEvent;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
/**
* 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.
*
* 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.
*
* 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)
*/
public class AnglesClassifier extends StrokeClassifier {
private HashMap<Stroke, Data> mStrokeMap = new HashMap<>();
public AnglesClassifier(ClassifierData classifierData) {
mClassifierData = classifierData;
}
@Override
public String getTag() {
return "ANG";
}
@Override
public void onTouchEvent(MotionEvent event) {
int action = event.getActionMasked();
if (action == MotionEvent.ACTION_DOWN) {
mStrokeMap.clear();
}
for (int i = 0; i < event.getPointerCount(); i++) {
Stroke stroke = mClassifierData.getStroke(event.getPointerId(i));
if (mStrokeMap.get(stroke) == null) {
mStrokeMap.put(stroke, new Data());
}
mStrokeMap.get(stroke).addPoint(stroke.getPoints().get(stroke.getPoints().size() - 1));
}
}
@Override
public float getFalseTouchEvaluation(int type, Stroke stroke) {
Data data = mStrokeMap.get(stroke);
return AnglesVarianceEvaluator.evaluate(data.getAnglesVariance())
+ AnglesPercentageEvaluator.evaluate(data.getAnglesPercentage());
}
private static class Data {
private final float ANGLE_DEVIATION = (float) Math.PI / 20.0f;
private List<Point> mLastThreePoints = new ArrayList<>();
private float mFirstAngleVariance;
private float mPreviousAngle;
private float mBiggestAngle;
private float mSumSquares;
private float mSecondSumSquares;
private float mSum;
private float mSecondSum;
private float mCount;
private float mSecondCount;
private float mFirstLength;
private float mLength;
private float mAnglesCount;
private float mLeftAngles;
private float mRightAngles;
private float mStraightAngles;
public Data() {
mFirstAngleVariance = 0.0f;
mPreviousAngle = (float) Math.PI;
mBiggestAngle = 0.0f;
mSumSquares = mSecondSumSquares = 0.0f;
mSum = mSecondSum = 0.0f;
mCount = mSecondCount = 1.0f;
mLength = mFirstLength = 0.0f;
mAnglesCount = mLeftAngles = mRightAngles = mStraightAngles = 0.0f;
}
public void addPoint(Point point) {
// Checking if the added point is different than the previously added point
// Repetitions are being ignored so that proper angles are calculated.
if (mLastThreePoints.isEmpty()
|| !mLastThreePoints.get(mLastThreePoints.size() - 1).equals(point)) {
if (!mLastThreePoints.isEmpty()) {
mLength += mLastThreePoints.get(mLastThreePoints.size() - 1).dist(point);
}
mLastThreePoints.add(point);
if (mLastThreePoints.size() == 4) {
mLastThreePoints.remove(0);
float angle = mLastThreePoints.get(1).getAngle(mLastThreePoints.get(0),
mLastThreePoints.get(2));
mAnglesCount++;
if (angle < Math.PI - ANGLE_DEVIATION) {
mLeftAngles++;
} else if (angle <= Math.PI + ANGLE_DEVIATION) {
mStraightAngles++;
} else {
mRightAngles++;
}
float difference = angle - mPreviousAngle;
// 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 (mBiggestAngle < angle) {
mBiggestAngle = angle;
mFirstLength = mLength;
mFirstAngleVariance = getAnglesVariance(mSumSquares, mSum, mCount);
mSecondSumSquares = 0.0f;
mSecondSum = 0.0f;
mSecondCount = 1.0f;
} else {
mSecondSum += difference;
mSecondSumSquares += difference * difference;
mSecondCount += 1.0;
}
mSum += difference;
mSumSquares += difference * difference;
mCount += 1.0;
mPreviousAngle = angle;
}
}
}
public float getAnglesVariance(float sumSquares, float sum, float count) {
return sumSquares / count - (sum / count) * (sum / count);
}
public float getAnglesVariance() {
float anglesVariance = getAnglesVariance(mSumSquares, mSum, mCount);
if (mFirstLength < mLength / 2f) {
anglesVariance = Math.min(anglesVariance, mFirstAngleVariance
+ getAnglesVariance(mSecondSumSquares, mSecondSum, mSecondCount));
}
return anglesVariance;
}
public float getAnglesPercentage() {
if (mAnglesCount == 0.0f) {
return 1.0f;
}
return (Math.max(mLeftAngles, mRightAngles) + mStraightAngles) / mAnglesCount;
}
}
}