[Spice-devel] [protocol RFC 0/2] RANDR support via QXLHead + SpiceHead

[Alon Levy]

On Mon, May 07, 2012 at 01:36:03PM +0300, Alon Levy wrote:
> On Mon, May 07, 2012 at 01:28:58PM +0300, Alon Levy wrote:
> > On Mon, May 07, 2012 at 12:01:42PM +0200, Gerd Hoffmann wrote:
> > >   Hi,
> > > 
> > > > But there is no concept of an additional surface in the guest driver.
> > > > RANDR 1.2 (and I think the same for 1.3, 1.4, since we don't have per
> > > > CRTC pixmaps) has a single screen wide pixmap. A screen is one per X
> > > > server, so there is just one even if you have multiple heads. And the
> > > > CRTCs scan out of it. To copy the RANDR docs diagram (removed the double
> > > > output):
> > > > 
> > > > 
> > > >        ┌─────────────────────────────────┐
> > > >     ┏━━━━━━━┳───────────────┐       ╔════════╗
> > > >     ┃   1   ┃               │       ║   A    ║
> > > >     ┃   ┏━━━╋━━━━━━━━━━━━━━━┫       ║        ║
> > > >     ┣━━━╋━━━┛               ┃       ╚════════╝
> > > >     │   ┃         2         ┃─────────────────┐
> > > >     │   ┃                   ┃        ╔═══════════════════╗
> > > >     │   ┃                   ┃        ║                   ║
> > > >     │   ┗━━━━━━━━━━━━━━━━━━━┫        ║        B          ║
> > > >     └───────────────────────┘        ║                   ║
> > > >     ┌──────┐  ┏━━━━┓  ╔══════╗       ║                   ║
> > > >     │screen│  ┃CRTC┃  ║output║       ╚═══════════════════╝
> > > >     └──────┘  ┗━━━━┛  ╚══════╝
> > > > 
> > > > So if we were to create an additional surface we will have to issue copy
> > > > commands for it from the primary surface.
> > > 
> > > I don't think you have to copy.  You have both width and stride fields
> > > for surfaces.  stride doesn't need to be width * depth, you can add
> > > padding.  Which allows you to allocate a large pixmap in device memory,
> > > then create multiple surfaces which each representing parts of your
> > > large pixmap.
> > 
> > OK, sorry, this was exactly what I had in mind for the client side
> > implementation of QXLHead, so I should have thought of it for the
> > additional surfaces as well.
> > 
> > > 
> > > The approach still has its drawbacks:  Rendering ops need some extra
> > > math, and you can't submit rendering ops for invisible regions of your
> > > large pixmap.  The biggest issue are overlapping crts I suspect.  They
> > > would lead to overlapping surfaces.  Ouch.
> > 
> > I don't follow. Your suggestion if I understand is to have a new surface
> > generated by the driver that uses the same image with different stride,
> > width, and starting location (allowing it to be a rect within the
> > primary surfaces) compared to the primary surfaces. The only problem is
> > that I don't think we have any notion of shared surfaces for the client
> > side - so you would still need to issue every rendering op twice (or do
> > the copy I suggested) by the server (guest issues one draw copy, server
> > issues two to client)? or we will need to expand the surface creation
> > command to allow this relation (in which case it would be similar to
> > QXLHead). My suggestion of QXLHead creates a shared bitmap
> > surface on the client side, so doesn't have this drawback. Am I
> > misunderstanding you?
> > 
> > > 
> > > I guess Izik had windows guests in mind which would probably deal fine
> > > with the multiple surfaces approach, given that the windows monitor
> > > layout dialog box allows alot less to do compared to xrandr ...
> 
> Forgot to mention, from reading the WDDM related docs (Video
> Presentation Network is the umbrella term, they have sources and

Mean Video Present Network, VidPN -
http://msdn.microsoft.com/en-us/library/windows/hardware/ff568500%28v=vs.85%29.aspx

> targets, respectively crtc and output in RANDR speak), it isn't clear if
> there can be a different surface for each source, but it is definitely a
> surface, so just extending QXLHead with a surface id (and the flags
> field Hans suggested can't hurt) would probably work. Or take your
> suggestion (the way I understand it) and add flags to the same effect to
> the SurfaceCreate message.
> 
> > > 
> > > cheers,
> > >   Gerd
> > > _______________________________________________
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