Rotating with Mouse using 2D

Question

Hello,
I have a shape created using GeneralPath and have hot-points once the user selects the Shape.I would like to add a feature which allows user to rotate the shape using/clicking&dragging the MOUSE.Can anyone please tell me how can I derive the angle between the shape center and mouse dragged position?Any sample code doing this.???
thanks

Answer 1

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
public class Rotation {
  public static void main(String[] args) {
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.getContentPane().add(new RotationPanel(200,100,100));
    f.setSize(400,300);
    f.setLocation(300,400);
    f.setVisible(true);
class RotationPanel extends JPanel {
  int cx, cy, size;
  double radians;
  Shape polygon;
  Area area, tabArea;
  int deltaX, deltaY;
  int shapeIndex = -1;
  boolean
    okToRotate = false,
    showTab = false;
  public RotationPanel(int cx, int cy, int size) {
    this.cx = cx;
    this.cy = cy;
    this.size = size;
    radians = 0;
    setBackground(Color.white);
    addMouseListener(new SelectionListener());
    addMouseMotionListener(new RotateListener());
  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D)g;
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                        RenderingHints.VALUE_ANTIALIAS_ON);
    int R = (int)(size / (4 * Math.cos(Math.PI/5) * Math.sin(Math.PI/5)));
    int[] x = new int[5];
    int[] y = new int[5];
    for(int i = 0; i < 5; i++) {
      x[i] = cx + (int)(R * Math.sin(radians*Math.PI/5));
      y[i] = cy - (int)(R * Math.cos(radians*Math.PI/5));
      radians += 2;
    polygon = new Polygon(x, y, 5);
    area = new Area((Shape)polygon);
    g2.setPaint(Color.blue);
    g2.draw(polygon);
    if(showTab) {
      int xR = cx + (int)(1.4 * R * Math.sin(radians*Math.PI/5));
      int yR = cy - (int)(1.4 * R * Math.cos(radians*Math.PI/5));
      //g2.draw(new Line2D.Double(cx, cy, xR, yR));
      int r = (int)(R * Math.cos(Math.PI/5));
      int xr = cx + (int)(1.4 * r * Math.sin((radians + 1)*Math.PI/5));
      int yr = cy - (int)(1.4 * r * Math.cos((radians + 1)*Math.PI/5));
      //g2.draw(new Line2D.Double(cx, cy, xr, yr));
      int[] xTab = new int[4];
      int[] yTab = new int[4];
      xTab[0] = x[0];
      xTab[1] = xR;
      xTab[2] = xr;
      xTab[3] = cx + (int)(r * Math.sin((radians + 1)*Math.PI/5));
      yTab[0] = y[0];
      yTab[1] = yR;
      yTab[2] = yr;
      yTab[3] = cy - (int)(r * Math.cos((radians + 1)*Math.PI/5));
      Polygon tabPolygon = new Polygon(xTab, yTab, 4);
      tabArea = new Area(tabPolygon);
      g2.setPaint(Color.red);
      g2.fill(tabPolygon);
  class SelectionListener extends MouseAdapter {
    public void mousePressed(MouseEvent e) {
      int x = e.getX();
      int y = e.getY();
      if(area.contains(x,y)) {
        deltaX = (cx - x);
        deltaY = (cy - y);
        shapeIndex = 1;
      if(showTab && tabArea.contains(x,y))
        okToRotate = true;
      else
        okToRotate = false;
    public void mouseReleased(MouseEvent e) {
      shapeIndex = -1;
      okToRotate = false;
    public void mouseClicked(MouseEvent e) {
      if(area.contains(e.getX(), e.getY()))
        showTab = true;
      else
        showTab = false;
      repaint();
  class RotateListener extends MouseMotionAdapter {
    public void mouseDragged(MouseEvent e) {
      int x = e.getX();
      int y = e.getY();
      if(shapeIndex > 0) {
        cx = x + deltaX;
        cy = y + deltaY;
      if(okToRotate) {
        int px = cx - x;
        int py = cy - y;
        int phi = (int)(Math.acos(py/Math.sqrt(px*px + py*py))*180);
        if(x < cx)
          phi *= -1;
        radians = phi * Math.PI/180;     
      repaint();
}