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convex hull - java

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private class PixelSection extends RecursiveAction {
/**
*
*/
private static final long serialVersionUID = 281227347488987878L;
ArrayList<Point> points;
ArrayList<Point> hullPoints;
Point longestDistanceA;
Point longestDistanceB;
int volume;
PixelSection(ArrayList<Point> points) {
this.points = points;
volume = points.size();
}
@Override
protected void compute() {
ConvexHull convexHull = new ConvexHull(points);
hullPoints = convexHull.points;
Point prev = null;
double longestDistance = 0;
for (int i = 0; i < hullPoints.size(); i++) {
try {
prev = hullPoints.get(i - 1);
} catch (Exception e) {
prev = hullPoints.get(hullPoints.size() - 1);
}
Point curr = hullPoints.get(i);
double adjacent = Math.abs(curr.x - prev.x);
double opposite = Math.abs(curr.y - prev.y);
double distance = Math.sqrt(Math.pow(adjacent, 2)
+ Math.pow(opposite, 2));
if (distance > longestDistance) {
longestDistanceA = new Point(prev.x, prev.y);
longestDistanceB = new Point(curr.x, curr.y);
longestDistance = distance;
}
}
}
private class ConvexHull {
ArrayList<Point> points;
public ConvexHull(ArrayList<Point> points) {
process(points);
}
private int cross(Point o, Point a, Point b) {
return (a.x - o.x) * (b.y - o.y) - (a.y - o.y)
* (b.x - o.x);
}
private void process(ArrayList<Point> points) {
Collections.sort(points, new PointComparator());
if (points.size() <= 1) {
return;
}
ArrayList<Point> lower = new ArrayList<Point>();
for (int i = 0; i < points.size(); i++) {
try {
while (lower.size() >= 2
&& cross(lower.get(lower.size() - 2),
lower.get(lower.size() - 1),
points.get(i)) <= 0) {
try {
lower.remove(lower.size() - 1);
} catch (Exception e) {
}
}
} catch (Exception e) {
}
lower.add(points.get(i));
}
ArrayList<Point> upper = new ArrayList<Point>();
for (int i = points.size() - 1; i > -1; i--) {
try {
while (upper.size() >= 2
&& cross(upper.get(upper.size() - 2),
upper.get(upper.size() - 1),
points.get(i)) <= 0) {
try {
upper.remove(upper.size() - 1);
} catch (Exception e) {
}
}
} catch (Exception e) {
}
upper.add(points.get(i));
}
try {
lower.remove(lower.size() - 1);
} catch (Exception e) {
}
try {
upper.remove(lower.size() - 1);
} catch (Exception e) {
}
lower.addAll(upper);
this.points = lower;
}
}
public class PointComparator implements Comparator<Point> {
public int compare(final Point a, final Point b) {
if (a.x < b.x) {
return -1;
} else if (a.x > b.x) {
return 1;
} else {
if (a.y < b.y) {
return -1;
} else if (a.y > b.y) {
return 1;
} else {
return 0;
}
}
}
}
}