SmoothCirclepublic class SmoothCircle extends Applet implements Runnable| An applet that displays a simple animation using double-buffering
and clipping |
| Fields Summary |
|---|
| int | x | | int | y | | int | r | | int | dx | | int | dy | | Dimension | size | | Image | buffer | | Graphics | bufferGraphics | | Thread | animator | | boolean | please_stop |
| Methods Summary |
|---|
| public void | init()Set up an off-screen Image for double-buffering // A flag asking animation thread to stop
size = this.size();
buffer = this.createImage(size.width, size.height);
bufferGraphics = buffer.getGraphics();
| | public boolean | mouseDown(java.awt.Event e, int x, int y)Allow the user to start and stop the animation by clicking
if (animator != null) please_stop = true; // if running request a stop
else start(); // otherwise start it.
return true;
| | public void | paint(java.awt.Graphics g)Draw the circle at its current position, using double-buffering
// Draw into the off-screen buffer.
// Note, we could do even better clipping by setting the clip rectangle
// of bufferGraphics to be the same as that of g.
// In Java 1.1: bufferGraphics.setClip(g.getClip());
bufferGraphics.setColor(this.getBackground());
bufferGraphics.fillRect(0, 0, size.width, size.height); // clear the buffer
bufferGraphics.setColor(Color.red);
bufferGraphics.fillOval(x-r, y-r, r*2, r*2); // draw the circle
// Then copy the off-screen buffer onto the screen
g.drawImage(buffer, 0, 0, this);
| | public void | run()The body of the animation thread
while(!please_stop) {
// Bounce the circle if we've hit an edge.
if ((x - r + dx < 0) || (x + r + dx > size.width)) dx = -dx;
if ((y - r + dy < 0) || (y + r + dy > size.height)) dy = -dy;
// Move the circle.
x += dx; y += dy;
// Ask the browser to call our paint() method to redraw the circle
// at its new position. Tell repaint what portion of the applet needs
// be redrawn: the rectangle containing the old circle and the
// the rectangle containing the new circle. These two redraw requests
// will be merged into a single call to paint()
repaint(x-r-dx, y-r-dy, 2*r, 2*r); // repaint old position of circle
repaint(x-r, y-r, 2*r, 2*r); // repaint new position of circle
// Now pause 1/10th of a second before drawing the circle again.
try { Thread.sleep(100); } catch (InterruptedException e) { ; }
}
animator = null;
| | public void | start()Start the animation thread
if (animator == null) {
please_stop = false;
animator = new Thread(this);
animator.start();
}
| | public void | stop()Stop the animation thread please_stop = true;
| | public void | update(java.awt.Graphics g)Don't clear the screen; just call paint() immediately
It is important to override this method like this for double-buffering paint(g);
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