[Development] Foreign windows, embedding and transiency

[Alberto Mardegan]

Hi all,
   while digging a bit more deeply into the code of QX11EmbedWidget (in 
order to port it to Qt5), I started wondering if we really need a 
special API for embedding, or whether QWindow could already offer most 
of it:

==========
   QWindow::QWindow(QWindow * parent)

   Creates a window as a child of the given parent window.

   The window will be embedded inside the parent window, its coordinates
   relative to the parent.
==========

What about adding an API to create QWindow objects for foreign windows 
as well? (by "foreign window" I mean a window created by another process)

Then we could provide embedding functionality by using the QWindow 
constructor or the QWindow::setParent() method. Also, the 
QWindow::setTransientParent() could be use to set our QWindow as 
transient for a foreign window.
Of course, this might not work in all platforms, but the documentation 
could explain where it works and where it doesn't.

In order to create a QWindow for a foreign window, there might be a 
special subclass of QWindow (QForeignWindow?) or maybe it could just be 
a QWindow with a special Qt::ForeignWindow flag (and maybe a constructor 
like QWindow::QWindow(WinId foreignWindow)).

Your opinions on which way foreign windows could be created (and on 
whether all of this sounds like a good idea to you) are very welcome. :-)

Ciao,
   Alberto