Preventing RootPane repaint on GlassPane repaint

Question

This question is similar to Paint on a glass pane without repainting other components. But I can't figure out how to apply the solution offered there.

My problem is that we have a very complicated RootPane, lots of components, and repainting it is expensive. We also have an animation running on the JFrame's GlassPane. I've noticed that every tick of the animation is repainting the animation as it should, but then also causing everything on the underlying RootPane to also be repainted.

I've tried overriding the paint() method for the RootPane with various code, but it always causes the components on the RootPane to be wiped and lots of flickering, probably from when child components try to repaint themselves as things update during the animation:

pnlContent = new JRootPane() {
   @Override
   public void paint(Graphics g) {
      OurGlassPaneWithAnimation glass = ...
      if (glass != null && glass.animation != null && glass.animation.isAlive()) {
         //Animation running, do something cool so root pane still looks good without repainting out the wazoo
      } else { super.paint(g); }
   }
};

Maybe putting the animation in a GlassPane is a bad idea? We've though about changing it to be in centered JPanel instead. Or is there a good way to do this using GlassPane and keeping the repaints done to the background RootPane to a minimum?

It sounds like you are doing something you shouldn't be inside `paint`, like changing state, changing the component tree, etc... Please consider posting a [minimal, complete example](http://stackoverflow.com/help/mcve) that reproduces the issue. Painting should be a strictly passive operation that can be run at any time. — Radiodef, Apr 21 '15 at 23:29
Generally speaking, a glass is transparent. This means that in order to paint it correctly, the paint engine MUST paint beneath it. You could try using something like [`JComponent#repaint(Rectangle)`](http://docs.oracle.com/javase/7/docs/api/javax/swing/JComponent.html#repaint(java.awt.Rectangle)) which defines the area you want updated, which might reduce the amount of painting that is performed — MadProgrammer, Apr 22 '15 at 00:35

medloh · Accepted Answer · 2015-04-22T16:32:22.107

@MadProgrammer Thanks for the suggestion doing a repaint(rect) instead of just a repaint() solved the problem. Now we can crank up the animation fps as high as we want and it doesn't noticeably affect the load time of the RootPane behind it. Here's the code snippet.

while (keepOnAnimating) {
   BufferedImage bi = vFrames.elementAt(0);
   if (bi != null) {
      // This only repaints area of image rect
      // Prevents lots of repaints from happening in rootpane behind glasspane.
      int x = getWidth() / 2 - bi.getWidth() / 2;
      int y = getHeight() / 2 - bi.getHeight() / 2;
      jc.repaint(x, y, bi.getWidth(), bi.getHeight());
  } else {
     jc.repaint();
  }
  ...
}

Preventing RootPane repaint on GlassPane repaint

1 Answers1