How to make a selection rectangle with draggable handles

Question

Hi,
I'm trying to write a program to visualize large trees in java. The idea is to have a thumbnail view of the tree with a movable selection rectangle that can be used to focus on certain parts of the tree. Parts inside the rectangle will be displayed in greater detail in another view.
I was wondering if there are any libraries available for making this kind of selection rectangle in Java2D (it'd also be nice to have 8 handles for changing the size of the rectangle) or if anyone has any implementation ideas. I'd appreciate any help. Thanks!
Wayne

Answer 1

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
import javax.swing.event.MouseInputAdapter;
public class DragLens extends JPanel
    Lens lens;
    public DragLens()
        lens = new Lens(this);
    protected void paintComponent(Graphics g)
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        lens.draw(g2);
    public static void main(String[] args)
        DragLens dragLens = new DragLens();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(dragLens);
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
class Lens extends MouseInputAdapter
    DragLens dragLens;
    Point2D.Double[] centers;
    Rectangle2D hunter;
    int selectedIndex;
    Point2D.Double offset;
    boolean dragging;
    final int S = 10;
    public Lens(DragLens dl)
        dragLens = dl;
        dragLens.addMouseListener(this);
        dragLens.addMouseMotionListener(this);
        initPoints();
        hunter = new Rectangle2D.Double(0,0,S,S);
        offset = new Point2D.Double();
        dragging = false;
    public void draw(Graphics2D g2)
        // draw rects
        g2.setPaint(Color.blue);
        for(int j = 0; j < centers.length; j++)
            g2.draw(new Rectangle2D.Double(centers[j].x-S/2, centers[j].y-S/2, S, S));
        // draw lines
        g2.setPaint(Color.red);
        g2.draw(new Line2D.Double(centers[0].x+S/2, centers[0].y+S/2,  // west
                                  centers[1].x+S/2, centers[1].y-S/2));
        g2.draw(new Line2D.Double(centers[1].x+S/2, centers[1].y-S/2,  // south
                                  centers[2].x-S/2, centers[2].y-S/2));
        g2.draw(new Line2D.Double(centers[2].x-S/2, centers[2].y-S/2,  // east
                                  centers[3].x-S/2, centers[3].y+S/2));
        g2.draw(new Line2D.Double(centers[3].x-S/2, centers[3].y+S/2,  // north
                                  centers[0].x+S/2, centers[0].y+S/2));
    public void mousePressed(MouseEvent e)
        Point p = e.getPoint();
        hunter.setFrameFromCenter(p.x, p.y, p.x+S/2, p.y+S/2);
        for(int j = 0; j < centers.length; j++)
            if(hunter.contains(centers[j]))
                offset.x = p.x - centers[j].x;
                offset.y = p.y - centers[j].y;
                selectedIndex = j;
                dragging = true;
                break;
    public void mouseReleased(MouseEvent e)
        dragging = false;
    public void mouseDragged(MouseEvent e)
        if(dragging)
            double x = e.getX() - offset.x;
            double y = e.getY() - offset.y;
            translate(x, y);
            dragLens.repaint();
    private void translate(double x, double y)
        switch(selectedIndex)
            case 0:
                centers[3].y = y;
                centers[1].x = x;
                break;
            case 1:
                centers[0].x = x;
                centers[2].y = y;
                break;
            case 2:
                centers[1].y = y;
                centers[3].x = x;
                break;
            case 3:
                centers[2].x = x;
                centers[0].y = y;
        centers[selectedIndex].x = x;
        centers[selectedIndex].y = y;
    private void initPoints()
        int[] x = { 0, 0, 1, 1 };
        int[] y = { 0, 1, 1, 0 };
        centers = new Point2D.Double[x.length];
        for(int j = 0; j < centers.length; j++)
            centers[j] = new Point2D.Double(x[j], y[j]);
        AffineTransform at = AffineTransform.getScaleInstance(80,40);
        at.translate(1,2);
        at.transform(centers, 0, centers, 0, 4);
}