import java.applet.*;
import java.awt.*;
import java.util.Vector;

public class SimpleCAD extends Applet {
  int w = 200;
  int h = 200;
  Vector lines = new Vector();
  int np = 0;
  int x1,y1;
  int x2,y2;
  int xl,yl;
  Image offImg;
  Graphics offGra;
  Button btnClear, btnUndo;
  
  public void init() {
    setLayout(new FlowLayout());
    btnClear = new Button("Clear");
    btnUndo = new Button("Undo");
    add(btnClear);
    add(btnUndo);
    setBackground(new Color(0).black);  
    setForeground(new Color(0).white);  
    }

  public void Dragupdate(Graphics g) {
    /*
    ** rubber-band effect
    */
    g.setXORMode(getBackground());
    setForeground(new Color(0).blue);
    if (xl != -1){
       // erase the old line
       g.drawLine(x1, y1, xl, yl);
       if (x2 != -1) {
          // draw the new one
          g.drawLine(x1, y1, x2, y2);
          }
       }
    }

  public void update(Graphics g) {
    // draw an offScreen drawing
    Dimension dim = getSize();
    if (offGra == null) {
      offImg = createImage(dim.width, dim.height);
      offGra = offImg.getGraphics();
      }
    offGra.setColor(new Color(0).black);
    offGra.fillRect(0,0,dim.width, dim.height);
    offGra.setColor(new Color(0).white);
    offGra.setPaintMode();
    for (int i=0; i < np; i++) {
       Rectangle p = (Rectangle)lines.elementAt(i);
       if (p.width != -1) {
          offGra.drawLine(p.x, p.y, p.width, p.height);
          }
       }
    // put the OffScreen image OnScreen
    g.drawImage(offImg,0,0,null);
    }

  public boolean handleEvent(Event e) {
    switch (e.id) {
      case Event.MOUSE_DOWN:
        // new starting point
        x1 = e.x;
        y1 = e.y;
        // begin an new drawing process
        x2 = -1;
        return true;
      case Event.MOUSE_UP:
        // end a drawing process
        lines.addElement(new Rectangle(x1, y1, e.x, e.y));
        np++;
        x2 = xl = -1;
        repaint();
        return true;
      case Event.MOUSE_DRAG:
        // xl yl line to be erased
        xl = x2;
        yl = y2;
        // x2 y2 last current point
        x2 = e.x;
        y2 = e.y;
        Dragupdate(getGraphics());
        return true;
      }
      return super.handleEvent(e);
    }

  public boolean action(Event e, Object o) {
    if (e.target == btnClear) resetDrawing();
    if (e.target == btnUndo)  undo();
    return true;
    }
 
  public void undo() {
    if (np>0) {
       lines.removeElementAt(np-1);
       np--;
       repaint();
       }
    }
  
  public void resetDrawing() {
    lines.removeAllElements();
    np=0;
    repaint();
    }
}