Class DrawableGroup

src/org/opensourcephysics/display/DrawableGroup.java:20–133

Draws a group of shapes. @author Wolfgang Christian @version 1.0

 * @version 1.0
 */
public class DrawableGroup implements Drawable {
  protected double x = 0, y = 0, theta = 0;
  protected ArrayList<Drawable> drawableList = new ArrayList<Drawable>(); // list of Drawable objects

  /**
   * Adds a drawable object to the drawable list.
   * @param drawable
   */
  public void addDrawable(Drawable drawable) {
    if((drawable!=null)&&!drawableList.contains(drawable)) {
      drawableList.add(drawable);
    }
  }

  AffineTransform trDG = new AffineTransform();

  /**
   * Draws the shapes in the drawable list.
   *
   * @param panel the drawing panel
   * @param g  the graphics context
   */
  @Override
public void draw(DrawingPanel panel, Graphics g) {
    int xpix = panel.xToPix(0);
    int ypix = panel.yToPix(0);
    
    Graphics2D g2 = (Graphics2D) g;
       
    double xt = x*panel.getXPixPerUnit()*Math.cos(theta)+y*panel.getYPixPerUnit()*Math.sin(theta);
    double yt = x*panel.getXPixPerUnit()*Math.sin(theta)-y*panel.getYPixPerUnit()*Math.cos(theta);
    AffineTransform at = g2.getTransform();
    trDG.setTransform(at);    
    trDG.rotate(-theta, xpix, ypix);
    trDG.translate(xt, yt);
    
    
    // was:
//    AffineTransform at = g2.getTransform();
//    at.concatenate(AffineTransform.getRotateInstance(-theta, xpix, ypix));
//    double xt = x*panel.getXPixPerUnit()*Math.cos(theta)+y*panel.getYPixPerUnit()*Math.sin(theta);
//    double yt = x*panel.getXPixPerUnit()*Math.sin(theta)-y*panel.getYPixPerUnit()*Math.cos(theta);
//    at.concatenate(AffineTransform.getTranslateInstance(xt, yt));

    g2.setTransform(trDG);
    for (int i = 0, n = drawableList.size(); i < n; i++) {
      drawableList.get(i).draw(panel, g2);
    }
    g2.setTransform(at);
  }

  /**
 * Sets the x and y coordinates.
 *
 * @param _x double
 * @param _y double
 */
  public void setXY(double _x, double _y) {