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

[Anthony Liguori <anthony@codemonkey.ws>]

Izik Eidus wrote:
> I personaly dont like mjpeg, and yes in the end of the day you can add
> the video streaming into vnc, but what is the point here?
>   

What I'm trying to understand is, what can we do with Spice that we 
couldn't possibly do with vnc.  That means understanding each feature 
and then figuring out if there's a vnc analog.

If there are compellingly unique features to Spice that can't be 
duplicated in vnc, then it's a no brainer.  If you can do most things in 
vnc but it would be hackish whereas Spice makes it all elegant, then 
provided we can merge Spice without a huge amount of pain, then it's a 
net win.

However, if we need to make a few changes to vnc in order to get the 
same performance as Spice, then it's not quite as clear that it's what 
we should be using.

We're talking about a major change here.  There is a ton of management 
software that assumes vnc today.  Even though there are Spice clients 
out there, there are embedded vnc clients in certain tools today along 
with java applets.

That's not to say we shouldn't embrace Spice, we just have to make sure 
we have a good reason to.

> We acctuly want to kick away that video streaming, and move into the
> DirectX and X video extentions video support (that will be made using
> the qxl driver) - will give much better performence.
>   

Okay, I suspect we're in agreement here then.

>> By the time we get to video memory, the display server has already 
>> straightened out what portions of the screen are visible and what 
>> aren't.  It will not render a hidden window and then render another 
>> window on top of it.
>>     
>
> I dont understand, if you have applciation that draw Rectangle, and
> just another Rectanlge on top of it, wont it hide it?, doesnt we want
> just to send the newest Rectangle?
>   

If you're using something like gdk, the toolkit double buffers windows 
by default and does a single flip on expose.  So this sort of thing 
never makes it way to the X server.  But the other point is, if you draw 
a rectangle with gdk, all the X server ever sees is the drawing of an image.

> Well any driver can use what ever spice commands it want, the X driver
> doesnt have to use all the spice commands, what is so bad about that?
>   

What I'm asking is what's the performance of the X driver vs. say, VNC?  
Do these high level operations really make sense for a Linux guest if we 
cannot ever implement them in an X driver?

I can see where this is a win with Windows because you can hook into 
GDI, but I'm not sure that this could ever do better than say, NX 
without something really clever or really deep integration with toolkits.

> Spice is not protocol for just windows or X or whatever, it id display
> protocol that implment common display commands that can be used over
> every display system.
>   

Are there plans to integrate Spice support in gdk (or cairo)?  I think 
that would be required to get performance parity with Windows.

Regards,

Anthony Liguori