<Swing Dev> JLayeredPane Questions

[Ben Loud]

I'm puzzled by JLayeredPane. It seems I can't change the layer of
component after it's been added to the layered pane and still get proper
repainting behaviour (except for JInternalFrames, because there's a
special case hack for those). The reason is that if I call setLayer(),
it doesn't revalidate the "optimizedDrawingEnabled" property. It remains
true even though there are now components on different layers, so a
component on layer 0 can paint on top of a component on layer 1. I've
attached a simple test case that demonstrates the problem.

Now, I was going to say that's a bug with an easy fix (call
validateOptimizedDrawing() in setLayer()), except that the JavaDoc for
setLayer(c, layer) says "Should be called before adding to parent". I
don't any justification for this limitation.

It's a little odd, since setLayer(c, layer) just calls straight in to
setLayer(c, layer, position), whose JavaDoc says nothing about when it
should or should not be called, so one would assume it should be safe to
call it at any time and still have things paint correctly. Surely this
must be the case, since why would the method take a position, if it's
only meant to be called before the component is added! A component
doesn't even have a position until it's added! But no, calling it will
not affect optimizedDrawingEnabled, so things will start painting
incorrectly.

I'd like to remove that line from the JavaDoc, and validate the
optimizedDrawingEnabled property whenever the layer of a component in
the layered pane changes, so that things always paint properly. I see
two ways of doing this:

The simplest is to simple call validateOptimizedDrawing() at the end of
setLayer(c, layer, position). This is the only possible way for AWT
Components. 

The way I'd probably prefer, atleast for JComponents, is to add a
listener for any changes to the LAYER_PROPERTY client property, for any
JComponents in the layered pane, and revalidate optimizedDrawingEnabled
whenever there's a change. The only downside to this is that there's a
static method putLayer() that sets this property, but specifies in the
JavaDoc that the method does not cause any side effects, including
repainting. But I don't see why you'd want that. 

Thoughts?

PS: It might be useful for any subclasses to make
validateOptimizedDrawing() protected.

PPS: validateOptimizedDrawing()'s criteria for disabling optimized
drawing is whenever any JInternalFrames or added, or if a component is
found whose layer is not FRAME_CONTENT_LAYER. Perhaps this could be
simplified to disabling whenever there are components on more than one
layer.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: Main.java
Type: application/octet-stream
Size: 2275 bytes
Desc: Main.java
URL: <http://mail.openjdk.java.net/pipermail/swing-dev/attachments/20080521/8f09e81e/Main.java>