Though forward declarations of the implementations are ok, it is cleaner
to have proper header files for each variant (default, kwin, quartz
right now). Of course these new header files are not installed and must
be kept private for build only.
In GimpPickButton, try to pick from the local window under the
cursor, before falling back to picking from the root window, so
that we can at least pick from local windows on Wayland.
The common code relies on X11 pointer grabbing semantics, which does
not work well on OS X. An attempt using event taps also proved
problematic, in particular with regard to setting the mouse cursor.
This patch implements a fully separate code for use on OS X platforms.
It works by simply overlaying the desktop with big transparent windows
on which the mouse cursor is set and motion events are captured. Evil,
but it works.
Michael Natterer