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/** USE EXISTING JAVA CLASSES **/
import java.awt.*;
import java.applet.Applet;
/** EXTEND THE JAVA APPLET CLASS AND IMPLEMENT THE RUNNABLE INTERFACE **/
public class AnimatorApplet3 extends Applet implements Runnable
{int frameNumber = -1;
// Define and/or initialize some
int delay;
// AnimatorApplet3 class variables.
Thread animatorThread;
boolean frozen = true;
Font font=new Font("TimesRoman",Font.BOLD,24);
String framestr = "";
int rval, gval, bval;
// Define red, green, blue color variables.
Dimension preImageDim;
// Define preImage variables needed to
Image preImage;
// create the offscreen copy of the image
Graphics preImageGraphics;
// we want to paint on the screen.
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public void init()
{String str;
int fps = 1;
// Define the default fps (frames per second).
str = getParameter("fps");
// Possibly, get HTML string specifying the
try
// fps.
{if (str != null)
{fps =
Integer.parseInt(str);} // If possible, convert HTML fps to an
}
// integer.
catch (Exception e) {}
// In case the try caused something strange.
delay = (fps > 0) ? (1000/fps):
100; // Convert fps to the milisecond delay
}
// time between frames.
/** CLICK TO START OR STOP THE APPLET **/
public boolean mouseDown(Event e, int x, int y)
{if (frozen)
{frozen = false;
start();}
else
{frozen = true;
animatorThread
= null; //
Instead of calling stop() here, since
}
// stop() now nullifies our preImage context,
return true;
// nullify only the animation thread in case
}
// we want to build on our current preImage.
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/** GENERATE AND/OR START THE ANIMATION THREAD **/
public void start()
{if (frozen) { }
// The animation is supposed to stay frozen.
else
// Otherwise, generate and/or start the
{if (animatorThread
== null) // animation thread. Apparently, if run
{animatorThread
= new Thread(this);} // breaks after catching an exception,
animatorThread.start();
// the animatorThread though not null
}
// will still need to be restarted.
}
/** CREATE AND DISPLAY FRAMES OF THE ANIMATION THREAD **/
public void run()
{setBackground(Color.white);
Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
// Set the priority low.
long startTime = System.currentTimeMillis();
// Remember start time.
while (Thread.currentThread()
== animatorThread)
// The animation loop.
{frameNumber++;
// Advance the frame number.
framestr = "Frame " + frameNumber;
// Create the frame string.
repaint();
// Display the frame.
try
// Sleep for the delay period.
{startTime += delay;
Thread.sleep(Math.max(0,
startTime-System.currentTimeMillis()));
}
catch (InterruptedException e) {break;}
// In case the try caused
}
// something strange, exit
}
// the while loop.
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/** CREATE THE CURRENT FRAME OF THE ANIMATION THREAD
**/
public void paint(Graphics g)
// This technique of painting by calling
{if (!frozen) update(g);}
// update, prevents the default (and hidden)
// behavior of update, and instead allows
public void update(Graphics g)
// the creation of an offscreen preImage
{Dimension d = size();
// preImage before painting the screen.
if ((preImageGraphics == null) ||
(d.width !=
preImageDim.width) ||
// Compare the current applet
(d.height !=
preImageDim.height))
// viewing size to our preImage,
{preImageDim = d;
// and if different, resize our
preImage = createImage(d.width,d.height);
// next preImage.
preImageGraphics = preImage.getGraphics();
}
preImageGraphics.setColor(getBackground());
// Clear the previous preImage
preImageGraphics.fillRect(0,0,d.width,d.height);
// by filling with the current
preImageGraphics.setFont(font);
// background color (white),
preImageGraphics.setColor(Color.blue);
// and then create the next
preImageGraphics.drawString(framestr,155,27);
// offscreen preImage.
for (int j = 40; j < (size().height
- 25); j += 30) // Set up vertical
spacing.
{for (int i = 5; i <
(size().width - 25); i += 30) // Set
up horizontal spacing.
{rval =(int)
Math.floor(Math.random()*256); // Generate a random
color
gval =(int)
Math.floor(Math.random()*256); // red, green, blue
mix.
bval =(int)
Math.floor(Math.random()*256); // Note the "casting"
here.
preImageGraphics.setColor(new
Color(rval,gval,bval)); // Draw a small box with
preImageGraphics.fillRect(i,j,25,25);
// the current random color.
preImageGraphics.setColor(Color.black);
// Draw a black border around
preImageGraphics.drawRect(i-1,j-1,26,26);
// the edge of the small box.
}
}
// Offscreen preImage completed.
g.drawImage(preImage,0,0,this);
// Paint preImage on the screen.
}
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/** STOP THE ANIMATION THREAD **/
public void stop()
{animatorThread = null;
// The user either clicked to stop or left the page,
preImageGraphics = null;
// so wipe out the current thread and preImage context.
preImage = null;
}
}