flicker : Java Glossary

by Roedy Green ©1996-2009 Canadian Mind Products
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flicker

Here are some things to try to avoid flicker:

In a Canvas.paint(), there is no need to call super.paint() since update() will have already cleared the screen.
In your update routine, don’t erase anything, just call paint. paint then must paint the entire Canvas. You override update() to just directly call paint() without the g.clearRect(0, 0, width, height);.
In your update routine, just erase the parts of the image that will become background, perhaps even only the parts that are not already background.
Use Swing which has double buffering built-in. You must override paintComponent rather than paint to get the automatic double buffering. Oddly, sometimes turning double buffering off with JComponent. setDoubleBuffered( false ) might help.
Use manual double buffering in AWT. Prepare all your images ahead of time with createImage and blast them to the screen (without erasing first) with drawImage in your paint routine. Because Images are platform dependent, you can’t simply instantiate them with a constructor. You have to create them through calls like Applet.getImage(), Component.createImage(), or Toolkit.getDefaultToolkit(). getImage().
In Windows, in Swing, you will see the entire screen repaint from time to time for no apparent reason, causing an annoying flicker. This is due to the fact that Swing uses DirectDraw for rendering which periodically redraws just to be safe. You can turn off DirectDraw and use standard Windows GDI rendering by starting Java with:
```
Java.exe -Dsun.java2d.noddraw=true MyClass
```
This will slightly slow down painting, however.
In Swing, use setOpaque( true ) to arrange for the system to draw the background in for you. This seems to work better than drawing it yourself with clearRect.
If you tie up the Swing thread, it can never get around to processing events and updating the screen. If you have entensive computation, start up a background thread and do your GUI work via SwingUtilities.invokeLater, or EventQueue.invokeLater.

This is a complicated topic. Tricks for AWT and Swing differ.

Sun’s tutorial on double buffering

Canvas
Image
paint
paintComponent
repaint
update

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