Client-side decorations, RGBA opaque regions

[Cody Russell <bratsche gnome org>]

Hi,

I'm working on adding support to GTK+ for doing client-side window
decorations, and there are a couple additional hints that seem like they
would be useful to propose.

Part of this work is involving changing GTK+ to use RGBA windows by
default.  For this, I'd like to propose an XserverRegion hint that
contains a region marking what parts of the window are known to be
opaque.  The idea being that this could be used by a WM/compositor to
optimize which parts of the window it needs to composite, if it's useful
to the WM/compositor (or it could be ignored; a GL compositor may not
find this kind of information very useful, for example).  This might be
called _NET_OPAQUE_REGION.

The other hint that would be useful is a hint similar to
_NET_FRAME_EXTENTS that specifies client-side drop shadow extents.  The
main idea here being that the WM could take advantage of this to know
where to perform window snapping for windows whose decorations and
drop-shadows are drawn client-side.  This might be called
_NET_SHADOW_EXTENTS.

Lastly, after reading the documentation about _NET_FRAME_EXTENTS [1] it
says that "the window manager MUST set _NET_FRAME_EXTENTS to the extents
of the window's frame."  If an application is drawing the decorations,
should it set this property?

Thanks,
   Cody

[1]. http://standards.freedesktop.org/wm-spec/1.3/ar01s05.html