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Re: [Qemu-devel] Ongoing changes to the displaying code

From: Jamie Lokier
Subject: Re: [Qemu-devel] Ongoing changes to the displaying code
Date: Sat, 10 Jan 2009 00:01:02 +0000
User-agent: Mutt/1.5.13 (2006-08-11)

Anthony Liguori wrote:
> >>Of course, with the right VNC extension to support a shared memory 
> >>transport, I still contend VNC can be just as efficient as SDL.
> >>    
> >
> >It still puts a big speed and flexibility limit IMHO.
> Why?  There's no additional memory copying.  There's a very small update 
> latency addition.

Fwiw, I agree with Anthony.

If VNC performance is a concern (it probably should be when you want
to do to video, or 1:1 full-screen, or 3d, or vsync-locked display),
extending localhost VNC to be as good as any "native" display method
can be would be the best way forward.

Obviously this would involve (at least) shared memory with both the X
server and QEMU, to remove all image copying and conversion when possible.
Similar mechanisms can be found on Windows and MacOS X.

SDL is good at some things but it's not perfect itself.  It may even
be better to remove SDL from QEMU proper, and provide a separate
localhost-VNC-to-SDL client.  (Same for the other frontends?)
Localhost-VNC does not need to support the whole VNC protocol, only
that used in localhost-VNC mode.

The other concern with VNC might be its complexity means you really
always want to use the existing VNC client library, which may not be a
desirable dependency for some applications.  For this, localhost-VNC
being both an extension to VNC and a subset of it would be helpful, as
you wouldn't have to use a full-fledged VNC client library for local
GUI apps if that isn't wanted.

-- Jamie

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