Re: [Qemu-devel] Re: Spice project is now open

[Anthony Liguori]

Paolo Bonzini wrote:
> On 12/12/2009 04:34 AM, Anthony Liguori wrote:
> > > Firefox uses that extensively, for example to render tiled backgrounds
> > > (though probably GTK user interface elements can do so less
> > > successfully).
> >
> > Yes, but this is just a single application.  The point is that these
> > things are not as widely standardized on X as they are on Windows.
>
> They are standardized (Xrender) and there are high-level de facto 
> standard APIs (Cairo or the Qt equivalent).

Cairo is pretty new and not widely used by applications yet.  But even 
Xrender is very limited compared to all of the things that GDI 
supports.  If it's just a matter of offloading Xrender, you could 
implement compositing in VNC fairly easily.

> Regarding compositing, this is done via OpenGL so even though it is 
> true that nothing goes through X calls, it is also true that 
> everything does go though a high-level API which can be sent on the 
> wire (cfr. AIGLX).

Right, but 3D is a different topic.  Spice doesn't address this today.

> Actually, compositing might really be where a protocol like SPICE 
> shines, since it does not generate nearly as many expose events, and 
> since you do not have to resend occluded contents on the wire any time 
> someone raises a window.

It's a trade off.  If you're sending each windows contents verses 
sending the visible screen, you're incurring an upfront cost assuming 
interaction will be improved.  This is something that I'd really like to 
see perf data on because.

> I have no idea how SPICE performs now, but there's definitely nothing 
> in a modern X Windows desktop that it cannot deal with.  The only 
> negative point it might have compared to Windows is IMO the rendering 
> of text.

I think the question I was raising was not whether Spice could handle X, 
but that given the things you can do with X, is all of Spice really 
needed.  IOW, would we get 99% of the way there with Xv accelerated 
overlays and Xrender based compositing for VNC?

BTW, can someone split out these VDI patches and get them on the list?  
Maybe at least an ETA of when that will happen.  I think it would make 
this whole discussion a lot more fruitful if we had more context..

Regards,

Anthony Liguori