Re: [Qemu-devel] X support for QXL and SPICE

[Dave Airlie <airlied@gmail.com>]

On Sat, Dec 12, 2009 at 1:31 PM, Anthony Liguori <anthony@codemonkey.ws> wrote:
> Soeren Sandmann wrote:
>>
>> Hi,
>>
>> Here is an overview of what the current QXL driver does and does not
>> do.  The parts of X rendering that are currently being used by cairo
>> and Qt are:
>>
>> - Most of XRender        - Image compositing
>>        - Glyphs
>>
>
> Does anything use Xrender for drawing glyphs these days?

Yes all of cairo apps and gtk, pretty much anything doing anti-aliased
fonts on a modern Linux desktop
uses X render to draw glyps. I think QT can use Xrender also but not
100% sure what the default is.
>
> Certainly, with a compositing window manager, nothing is getting rendered by
> X...

Yes there is, with a GL compositing window manager nothing is rendered
by X, with an Xrender
compositing window manager (metacity or kwin xrender mode). Also
allanti-aliased font operations, and
a number of cairo operations are done using xrender, which means most
of the modern desktop,
I actually broke sw fallbacks to the frontbuffer on my driver last
week and it took me nearly a half a day to realise it.

X rendering in modern apps is like Soeren describes, render to
offscreen pixmap, copy to onscreen.

> Scrolling is accelerated in VNC.  In the Cirrus adapter, both X and Windows
> use a video-to-video bitblt, we use this to create a VNC CopyRect which
> makes scrolling and Window movement smooth.

Firefox scrolling? (though I'm not sure anyone deals with it sainly).

>
>> However, as things stand right now, there is not much point in adding
>> this support, because X applications essentially always work like
>> this:
>>
>>        - render to offscreen pixmap
>>        - copy pixmap to screen
>>
>> There is not yet support for offscreen pixmaps in SPICE, so at the
>> moment, solid fill and CopyArea are the two main things that actually
>> make a difference.
>>
>
> Okay, that's in line with what my expectations were.  So what's the future
> of Spice for X?  Anything clever or is Windows the only target right now?
>

If spice grows offscreen surfaces along with some a few more rendering
operations I expect we can make it go fairly fast for most X apps. Since
at RH we have both spice and X teams I think we can probably produce
some sort of collaborative plan in the short term on how to go forward.

Dave.