X.org version X11R6.8.0 contains experimental support for a new X protocol extension called Composite. This extension allows windows to be drawn into pixmaps instead of directly onto the screen. In conjunction with the DAMAGE and RENDER extensions, this allows a program called a composite manager to blend windows together to draw the screen.
Performance can be improved by enabling the
RenderAccel option in xorg.conf. See
Appendix D, X
Config Options for more details.
Full Composite support will require additional driver support.
Currently, direct rendering clients such as GLX have no way of
knowing that they are supposed to render into a pixmap, and will
draw directly to the screen instead. We are currently investigating
what is necessary for such clients to interoperate seamlessly with
Composite. In the meantime, GLX will be disabled by default when
the Composite extension is detected. An option has been provided to
re-enable it. See
AllowGLXWithComposite in Appendix D, X
This issue was discussed on the xorg mailing list: http://freedesktop.org/pipermail/xorg/2004-May/000607.html
Composite also causes problems with other driver components:
Xv cannot draw into pixmaps that have been redirected offscreen and will draw directly onto the screen instead. For some programs you can work around this issue by using an alternative video driver. For example, "mplayer -vo x11" will work correctly, as will "xine -V xshm". If you want to use Xv, you can simply disable the compositing manager and re-enable it when you are finished.
Workstation overlays are incompatible with Composite.
More information about Composite can be found at http://freedesktop.org/Software/CompositeExt