OpenGL in USB Display Devices under wayland

[Sannu K]

On Sun, Jun 24, 2012 at 12:59 PM, Pekka Paalanen <ppaalanen at gmail.com>wrote:

> On Sat, 23 Jun 2012 22:21:28 +0530
> Sannu K <sannumail4foss at gmail.com> wrote:
>
> > On Sat, Jun 23, 2012 at 2:04 AM, Casey Dahlin <cdahlin at redhat.com>
> wrote:
> >
> > > On Fri, Jun 22, 2012 at 10:29:04PM +0300, Pekka Paalanen wrote:
> > > > The trick is in the kernel DRM, which has to be able to deal with the
> > > > buffer and actually push it to the USB device. This may require
> special
> > > > allocation flags or somehow using the dmabuf infrastructure to
> allocate
> > > > the buffer, where the composite is drawn.
> > >
> > > Pretty sure it's possible right now to just copy the buffer out to
> normal
> > > userspace memory and then in to another DRM buffer. Not the quickest
> > > transition, but functional.
> > >
> > > --CJD
> > >
> >
> > Does this mean wayland (rather weston) does not support multiple graphics
> > card seamlessly (as of now without dmabuf patches)?
>
> To my understanding, for now, correct.
>
> > Consider that an
> > application creates a DRM buffer and uses it for rendering, when user
> moves
> > the window to another screen that is driven by another graphics card this
> > case could appear. Will the memory content be copied (in current state)?
>
> In current state, I do not think it would work at all.
>
> You do not even have to think that far. Just think about how Weston
> composites per output, and how a resulting buffer could be used on
> an output that is on a different graphics card than what Weston uses
> for compositing.
>
> I have also never heard of a Wayland developer using a multi-card setup.
>
> > Will there be a better solution without buffer sharing (what if the
> window
> > buffer is in graphics card's RAM)? Please provide some pointers and/or
> > documentation on how wayland and weston works (which libraries it calls
> for
> > what purpose).
>
> I don't think it works right now. Anyway, the libraries are the usual:
> libdrm, Mesa (GBM). And of course the kernel DRM. You can look at Weston's
> DRM backend.
>
> Just like for many other concerns, you can be sure (I am, at least) that
> all this will work somehow, some day. There are just more pressing
> matters for now.
>
> A key point here is to realise, that GPU interoperability is not
> really a Wayland problem, but a problem for the whole graphics stack.
>
>
> Thanks,
> pq
>

Thanks for the details. Hope the multi GPU setup will come soon to wayland
and weston.
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