Re: subwindow-less Gtk+ and offscreen windows

[Jean-Philippe Chancelier <jpc cermics enpc fr>]

    Lieven> For OpenGL, something we could do is let the OpenGL
    Lieven> widget's user render to an offscreen buffer, and when he's
    Lieven> done, blit the whole result to the target window. This
    Lieven> way, all the stuff like overlapping windows will still
    Lieven> work with opengl widgets, like with any other widget. It
    Lieven> may have a slight performance impact, but I think it will
    Lieven> be really minimal if the blitting is done by the hardware
    Lieven> (so no cpu reading back from video mem). Of course we'll
    Lieven> have to do a performance test before we implement
    Lieven> something like this, but I think it might work.

    I use gtkglext for rendering opengl graphics in a Gtkwindow 
    and it can be used as you describe i.e render in an offscreen buffer 
    managed by the GtkWindow or directly render in the GtkWindow. 
    The two modes seams not that different when performance is considered 
    and for the kind of graphics I realized.
    But rendering in an offscreen buffer with opengl crashed (in a recent past) 
    the application and/or the X server on some architectures/configuration 
    (for example on dell machines with intel graphics). 
    jpc