XComposite Overlay Window usage

Jochen Keil j.keil at gmx.de
Tue Sep 24 12:48:06 PDT 2013

Hello Chris,

On 23.09.2013 15:19, Chris Wilson wrote:
> 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).

thanks for your reply. I looked for documentation for XV_ALWAYS_ON_TOP,
but couldn't find any. Is there documentation available somewhere?

However, I figured, that what I'd like my application to do resembles
more a compositing manager. In particular I wanted my windows to become
transparent only on overlapping parts. For example I have an focused
window which is partially occluded by an unfocused window. The unfocused
window would then be drawn transparently over the focused window. Thus I
think it'd be more appropriate to write a plug-in for an existing
compositing manager.

Best wishes,

> -Chris

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