Re: [Qemu-devel] [PATCH] opengl rendering in the sdl window

[Daniel P. Berrange]

On Mon, Sep 08, 2008 at 04:47:00PM +0100, Daniel P. Berrange wrote:
> On Mon, Sep 08, 2008 at 04:08:01PM +0100, Jamie Lokier wrote:
> > Gerd Hoffmann wrote:
> > > Beside that I still think it would be a good idea to separate qemu and
> > > the gui into two separate processes, so you can close the GUI window and
> > > keep the VM running.  It also solves the dependency issue for distros as
> > > the gtk frontend with all the dependencies can just go into a separate
> > > sub-package.
> > 
> > Extending VNC with a "shared memory" extension, similar to Xlib's
> > MIT-SHM extension, and implementing it in QEMU and Gtk-VNC would be a
> > nice way to do this.
> 
> Funny you should mention that. Anthony had code todo exactly that against
> for both QEMU and GTK-VNC a while back. We had it in the GTK-VNC for a 
> short while but removed it due to some race conditions in its impl, and
> it interracted badly with our OpenGL impl. We could easily revisit this
> idea if it were thought to be important / useful.

Just thought I'd mention one other thing - it is not actually clearcut / or
guarenteed that XShm + VNC would improve performance in all circumstances.
This is because X pixmaps created via XShm apparently cannot live in video
memory, and thus it is not so easy to get full performance advantage of
hardware acceleration - this could impact scaling for example. The need to
perform XSync operations when updating the pixmaps may also negate the
benefit of avoiding the socket I/O. It would all depend on the size of the
updates vs frequency of them. Still defintely worth a try to see what kind
of difference Shm makes in a real world scenario with QEMU.

Daniel
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