Thanks for the responses guys.
1. System.setProperty("sun.awt.noerasebackground", "true");
This will turn off automatic background clearing
of AWT components, which GLCanvas is based on.
This seems to only not redraw it during resizing.
I've set up a JFrame with no other components.
The window shows the default light blue color (I think) . If I don't set the property, then it resizes and retains it's color. If I set the property to true, then it shows through during resize, but leaves rubbish behind at intervals where the border was as it resized, and it also fills out with colour when i finish the resize. unfortunately not transparent.
Perhaps i'm missing something.
2. Use the Robot class to capture an image of
your desktop and turn it into a JOGL texture
which you use to fill the background of your
window.
This smells very CPU intensive. Especially when I will have at least one canvas the size of the screen ALWAYS as the bottom-most window. if I have to grab a texture for every window that's open over the canvas 23 times per second (if thats my refresh rate), this is going to hurt performance hugely.
Hmmmm.
Ken, I'll have to read your response again, perhaps a few times, to see what I have to do on that idea.

Ta.
Greg.