// file:    testGraphics4.java
// author:  Robert Keller
// purpose: Showing how to redefine update.
//          

/* In this program, we over-ride the 'update' method of the base Frame.

   This is the standard model for flicker-free graphics in the JDK 1.0 AWT.

   By over-riding update, we can have it not draw the background at all.
   Then we call paint and have it draw the off-screen image, which has
   its own background.

   Compare with testGraphics3a, where there can be some flicker.  Here there 
   is no flicker.  The image motion is a bit jerky because the step size 
   is fairly large (10 pixels).  We could make the step size smaller, but 
   then the image would not appear to move as fast.
*/

import java.awt.*;                      // to get awt (abstract window toolkit)
import java.lang.Thread;

class testGraphics4 extends Frame       // needed to allow over-ride of paint
{                                       // consider this to be magic for now

Image image;                            // image provides graphics buffer

// paint(Graphics) will be called by the system to paint the Frame when 
// necessary.  At that time, the Graphics of the frame will be passed as 
// an argument.

public void paint(Graphics g)
  {
  g.drawImage(image, 0, 0, null);
  }


public void update(Graphics g)
  {
  paint(g);
  }

// draw stuff at position x, y

void drawStuff(int x, int y)
  {
  Graphics g= image.getGraphics();
  g.setColor(Color.white);                        // paint image background
  g.fillRect(0, 0, image.getWidth(null), image.getHeight(null));

  g.setColor(Color.black);                        // set the color for drawing
  g.drawRect(x+50, y+50, 400, 300);               // draw a rectangle

  g.setColor(Color.blue);
  g.fillOval(x+100, y+100, 300, 200);             // fill an oval

  g.setColor(Color.yellow);
  g.drawOval(x+100, y+100, 300, 200);             // draw an oval

  g.setFont(new Font("Times", Font.BOLD, 28));  
  g.drawString("Harvey Mudd College", x+140, y+210);  // draw a string
  }


public static void main(String[] arg)
  {
  testGraphics4 frame = new testGraphics4();      // create the frame

  frame.reshape(50, 50, 600, 500);                // set the location and size

  frame.show();                                   // show the frame 

  // Note: the following must be done AFTER the frame is shown.

  frame.image = frame.createImage(frame.size().width, frame.size().height);

  for( int i = 0; i < 100; i += 10 )
    { 
    frame.drawStuff(i, i);
    try{Thread.sleep(5);} catch(Exception e){}  // delay 5 milliseconds
    frame.repaint();
    }
  }
}