The current Swing implementation in JDK 1.4 on X11 cannot tell if a paint event
following a scroll (XCopyArea) of a JViewport is as a result of some sequence
of GraphicsExpose events or some other "normal" paint event after scrolling.
So a paint event after a scroll will be a full viewport repaint.

There is a method that swing can call to determine the obscurity state of
the window but this is unimplemented on X11 (solaris and Linux) and
consquently returns a value that will forgo the optimisation that can
result.

This method should be implemented.