XComposite Overlay Window usage

[Chris Wilson]

On Mon, Sep 23, 2013 at 01:23:08PM +0200, Jochen Keil wrote:
> Hello,
> 
> I'm trying to write an application with which I'd like to draw "over"
> other windows. So far my attempts have been:

> * Drawing to an transparent overlay window I create myself: Main problem
> is to keep this window always on top of of all the other windows
> (repeated calls to XRaiseWindow, possible flicker) + requires a
> compositing manager.

I took this approach (using the hw overlay plane), plus a
XV_ALWAYS_ON_TOP attribute. (Eliminates the raise requirement, and
allows the user to write to the scanout without waking the GPU.) Using
the overlay also ensures that it appears over all windows, including the
compositing manager or fullscreen games (without interferring with those).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre