/*
   This applet demonstrates how an applet can respond when
   the user drags the mouse.  The user can draw on the applet
   by dragging the mouse.  Right-click on the applet to
   clear it.  (This applet does not preperly deal with
   changes in size.)
 */

import java.awt.*;
import java.awt.event.*;
import java.applet.Applet;

public class applet_draw extends Applet implements MouseListener, MouseMotionListener {
    Image offscreen;     // an offscreen image, to hold a copy of the sketch for repainting
    Graphics bufferGraphics;  // graphics context for drawing to offscreen
    
    public void init() {
        // Initialize the applet.
        setBackground(Color.white);
        addMouseListener(this);         // Register the applet to receive
        addMouseMotionListener(this);   //   mouse events from itself.
    }
    
    public void update(Graphics g)  {
        // override this to avoid erasing the applet before drawwing
        paint(g);
    }
    
    public void paint(Graphics g) {
        // copy the off-screen image to the applet, creating it first
        // if it does not already exist
        if (offscreen == null)
            makeoffscreen();
        g.drawImage(offscreen,0,0,this);
    }
    
    void makeoffscreen() {
        // create the off-screen image and graphics context
        offscreen = createImage(getSize().width,getSize().height);
        bufferGraphics = offscreen.getGraphics();
        clearImage();
    }
    
    void clearImage() {
        // make the off-screen image into a white rectagle with a red border
        bufferGraphics.setColor(Color.white);
        bufferGraphics.fillRect(0,0,getSize().width,getSize().height);
        bufferGraphics.setColor(Color.red);
        bufferGraphics.drawRect(0,0,getSize().width - 1,getSize().height - 1);
        bufferGraphics.setColor(Color.black);
    }
    
    void drawLine(int x1, int y1, int x2, int y2) {
        // Draw a line from (x1,y1) to (x2,y2) both on the off-screen
        // image and on the applet itself.  This keeps the two
        // images in proper sync.
        bufferGraphics.drawLine(x1,y1,x2,y2);
        Graphics g = getGraphics();  // Graphics context for drawing to the applet.
        g.drawLine(x1,y1,x2,y2);
        g.dispose();
    }
    
    boolean dragging = false;  // This is true when a drag is in progress.
    int prev_x;  // Previous position of cursor during a drag.
    int prev_y;
    
    public void mousePressed(MouseEvent evt) {
        // If user right-clicks the applet, clear the image;
        // otherwise start drawing by setting dragging = true
        if (offscreen == null)
            makeoffscreen();
        if (evt.isMetaDown()) {
            clearImage();
            repaint();
        } else {
            dragging = true;
            prev_x = evt.getX();
            prev_y = evt.getY();
        }
    }
    
    public void mouseDragged(MouseEvent evt) {
        // Draw a line from previous mouse position to current
        // position, but only if a drag is in progress.
        if (dragging) {
            int new_x = evt.getX();
            int new_y = evt.getY();
            drawLine(prev_x, prev_y, new_x, new_y);
            prev_x = new_x;
            prev_y = new_y;
        }
    }
    
    public void mouseReleased(MouseEvent evt) {
        // Finish off the drag, if one is in progress.
        if (dragging) {
            int new_x = evt.getX();
            int new_y = evt.getY();
            drawLine(prev_x, prev_y, new_x, new_y);
            dragging = false;
        }
    }
    
    public void mouseClicked(MouseEvent evt) { }  // required by listener interface
    public void mouseEntered(MouseEvent evt) { }
    public void mouseExited(MouseEvent evt) { }
    public void mouseMoved(MouseEvent evt) { }
    
}