Phoenix Revived said the following:
While this may all be true, WebKit/Gtk+ with DirectFB seems to be able to render irregular windows just fine. I haven't been able to figure out how they do it by perusing the code - I was hoping someone here knew.
I did a little digging and this may be what you're looking for. The following e-mail tells how the webkit developer handles the situation you describe: http://lists.macosforge.org/pipermail/webkit-dev/2008-October/005372.html. Particularly interesting is point 3 which explains how the developer works around the problem.
-- José Alburquerque jaalburquerque cox net