Passive vs. Active Rendering
Trail: Bonus
Lesson: Full-Screen Exclusive Mode API

Passive vs. Active Rendering

As mentioned before, most full-screen applications usually function better if they are at the helm during drawing. In traditional windowed GUI applications, the question of when to paint is usually handled by the operating system. When operating in a windowed environment, this makes perfect sense. A windowed application does not know when the user is going to move, resize, expose, or cover an application by another window until it actually happens. In a Java GUI application, the operating system delivers a paint event to the AWT, which figures out what needs to be painted, creates a java.awt.Graphics object with the appropriate clipping region, then calls the paint method with that Graphics object:

// Traditional GUI Application paint method:
// This can be called at any time, usually 
// from the event dispatch thread
public void paint(Graphics g) {
    // Use g to draw my Component

This is sometimes referred to as passive rendering. As you can imagine, such a system incurs a lot of overhead, much to the annoyance of many performance-sensitive AWT and Swing programmers.

When in full-screen exclusive mode, you don't have to worry anymore about the window being resized, moved, exposed, or occluded (unless you've ignored my suggestion to turn off resizing). Instead, the application window is drawn directly to the screen (active rendering). This simplifies painting quite a bit, since you don't ever need to worry about paint events. In fact, paint events delivered by the operating system may even be delivered at inappropriate or unpredictable times when in full-screen exclusive mode.

Instead of relying on the paint method in full-screen exclusive mode, drawing code is usually more appropriately done in a rendering loop:

public void myRenderingLoop() {
    while (!done) {
        Graphics myGraphics = getPaintGraphics();
        // Draw as appropriate using myGraphics

Such a rendering loop can done from any thread, either its own helper thread or as part of the main application thread.

Programming Tips

Some tips about using active rendering:

Previous page: Display Mode
Next page: Double Buffering and Page Flipping