Draw image using paint() only once.

Question

I am having performance issues with my application. It is creates a graph like data display. The display is static. However each time paint is called the image is re-rendered. I want it only rendered once to improve performance, I tried to do this using the following code:
public void paint(Graphics g){
          if (alreadyRun) return;
          //super.paint(g);
          alreadyRun = true;
// draw graphics code
}Unfortunately the required image appears for a moment then disappears. Is there any way to render the image only once? Also, are there any other performance improving measures I can take? I was thinking of rendering only the part of the image that appears on screen (my graphics display is usually bigger than the actual screen size)

Answer 1

The common way to deal with performance like this is to draw the graph (or whatever) onto a BufferedImage then have the paint (or paintComponent in Swing) simply draw the image. The single draw image is quite fast and keeps the pixel values persistant across paints. If you already have a single image as the thread title hints, the paint shouldn't create much of a performance hit. The reason you are seeing your image disappear is that any time a window is resized, repacked, moved, covered up, or a multitude of other reasons, it calls paint again, so even with static data, there will be times the paint method is called again, causing your drawing to disappear.