Positioning and Multi display support for Weston Wayland

Fri May 18 10:24:22 UTC 2018

On Fri, 2018-05-18 at 13:08 +0300, Pekka Paalanen wrote:
> On Fri, 18 May 2018 08:25:26 +0000
> Sandeep Chandak <ba.sandeep at tataelxsi.co.in> wrote:
> 
> > Hi Pekka,
> > 
> > Thanks for a detailed response, need some more clarifications
> > though
> > 
> > The final solution will use drm-backend we are in process of
> > getting
> > the drm-backend work on the platform, while we use x11-backend for
> > development.
> > 
> > a)  I assume from Shared-CRTC support you mean monitors with same
> > resolutions, refresh rate etc. So cloned mode is supported for use
> > cases for displays with similar properties for resolution, refresh
> > rate etc.
> 
> Yes. It literally means using the same CRTC to feed several
> connectors,
> which means they share the video mode and timings. This requires
> explicit support in hardware, and whether it is available varies
> between chips.
> 
> > Is this supported for x11-backend also?
> 
> Not currently, and there are no plans to do so. You would simply have
> two windows with the same content, and I'm not sure what the benefit
> of
> supporting that would be. The only visible difference is that all
> heads
> advertise their own wl_output globals, so in clone mode you would get
> two (or more) wl_outputs that behave identically while reporting
> per-monitor details.
> 
> If independent-CRTC mode worked, you could just use that with the
> x11-backend, as the only difference with a proper configuration would
> be the output timings, and the x11-backend is bad with timings
> anyway.
> 
> > As you mentioned
> > Independent-CRTC mode (i.e monitors with different refresh rate
> > etc),
> > cloning is not supported currently. Can you please confirm if this
> > understanding is correct?
> 
> Yes.
> 
> You can read more about the clone mode design here:
> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fph
> abricator.freedesktop.org%2FT7727&data=02%7C01%7Cmarius-
> cristian.vlad%40nxp.com%7Cfa1425f456fb4107c98e08d5bca75666%7C686ea1d3
> bc2b4c6fa92cd99c5c301635%7C0%7C0%7C636622349257323713&sdata=tFViB1BXM
> 5Yct6wifjnZbaja7dmWYu1pdvWNAK3phv8%3D&reserved=0
> 
> > b) Different configuration for us means - Either a single or
> > multiple
> > compositor instance (running on same physical hardware) driving
> > different monitors to display different composited content. In this
> > case the displays can be placed far off from each other. I assume
> > this would be supported. Please confirm? 
> 
> Sorry, I'm not sure I understand. The only case I have talked about
> here is a single Weston compositor instance controlling all outputs.
> 
> It has been impossible to run more than one compositor instance on
> the
> same DRM device node, and this is still true today with Weston. DRM
> leases is a new kernel feature that would allow one compositor to
> "lease" some display resources to another compositor instance, but
> the
> Weston support for giving out leases is only coming, and Weston
> running
> on a lease development has not started yet AFAIK.

Some attempts have been posted albeit they haven't got too much review,
and will have to be adapted due to clone changes. 

https://lists.freedesktop.org/archives/wayland-devel/2018-February/0369
47.html

> 
> If your system has multiple display devices (DRM card device nodes),
> then it should be possible to run a Weston instance on each
> simultaneously, though I'm not sure it has been tested.
> 
> Different Weston instances are naturally independent from each other,
> but the outputs inside a single instance are all naturally part of
> the
> same extended desktop without isolation between the outputs. It is
> possible to write code to isolate outputs at the window manager
> level,
> but I'm not sure it would be enough for a nice user experience. Hence
> for independent seats, I would recommed separate Weston instances.
> 
> If your aim is to use a single computer to drive several physical
> seats
> (monitors, input devices), then if you have a DRM card device node
> for
> each seat it should be mostly a configuration issue to get that
> running. If you need to share the same DRM card node between several
> physical seats, then you would need a single host compositor and
> guest
> compositors for each seat. This could use DRM leases, fullscreen-
> shell
> extension, or normal fullscreen windows in the host compositor, but I
> believe they would all require some development effort.
> 
> > c) Extended/Tiled mode for us means - Multiple monitors connected
> > to
> > form a larger display (e.g. Video wall use case), just wanted to
> > confirm can this be achieved with a single compositor instance?
> 
> Theoretically yes, in practice the current state of Weston might fall
> a
> little short.
> 
> The extended mode is the only mode Weston does at the moment, so
> that's
> good. Where it falls short are output timings (we have nothing to
> actually synchronize the output refresh cycles, so you can have
> timing
> differences up to the longest refresh period) and layout
> configuration,
> as I mentioned before. I do think that developing Weston to implement
> these lacking features would be welcome. Synchronizing outputs will
> need also kernel driver and API support, mind.
> 
> 
> Thanks,
> pq
> 
> 
> > -----Original Message-----
> > From: Pekka Paalanen [mailto:ppaalanen at gmail.com] 
> > Sent: 17 May 2018 17:48
> > To: Sandeep Chandak <ba.sandeep at tataelxsi.co.in>
> > Cc: wayland-devel at lists.freedesktop.org
> > Subject: Re: Positioning and Multi display support for Weston
> > Wayland
> > 
> > On Wed, 16 May 2018 06:41:08 +0000
> > Sandeep Chandak <ba.sandeep at tataelxsi.co.in> wrote:
> > 
> > > Hi,
> > > 
> > > We are using Weston Wayland based compositing for our solution,
> > > though we are able to render image, video text etc.
> > > 
> > > We are using x11 backend along with desktop shell to build the 
> > > solution which requires rendering of multiple media contents
> > > (image, videos etc) together. We are using following versions of
> > > packages 
> > 
> > Hi,
> > 
> > I presume the x11-backend is only for development purposes and the
> > final product will run on DRM-backend instead.
> > 
> > > 
> > > a)       Weston - version 5.0
> > > 
> > > b)      Wayland - version 1.15.0
> > > 
> > > c)       Ubuntu 16.04
> > > 
> > > d)      Hardware - Intel i5 processors
> > > 
> > > e)      Cairo - 1.14 with EGL/OpenGL ES enabled
> > > 
> > > We have below queries for which we need some inputs
> > > 
> > > 
> > > a)       Positioning of windows - We would like to position
> > > windows
> > > to a specific x,y location. However, we see that Weston positions
> > > it at a random location. We would like to confirm if positioning
> > > of 
> > > windows to specific location is supported by Weston.  
> > 
> > No, you cannot position windows from the application into specific
> > x,y coordinates chosen by the application. There are a couple of
> > design approaches to achieve the positioning you want:
> > 
> > What I would personally recommend is to modify the window manager
> > to
> > position your windows appropriately. You may need to write a new
> > protocol extension so that the application can tell the special
> > role
> > of the window to the compositor, so that the compositor can place
> > it
> > correctly in the space it happens to have available.
> > 
> > You could also write a protocol extension to allow explicit
> > positioning of windows from applications, but that will have the
> > problem that any single application will be completely unaware of
> > any
> > other applications' windows or desktop elements. Explicit
> > positioning
> > in applications may seem like an easy solution at first, but it
> > really only works in extremely narrow use cases. I consider it as a
> > workaround, not a solution.
> > 
> > However, depending on your use case, there might be much more
> > straightforward solutions.
> > 
> > > 
> > > b)      Multi display Support - We need to support following use
> > > cases and would like to confirm if this is currently supported
> > > by 
> > > Weston?
> > > 
> > > *       Cloned display (same content on multiple screens)  
> > 
> > Shared-CRTC clone mode is available in Weston upstream master
> > branch,
> > but the final patch to allow it to be configured is not yet
> > reviewed:
> > https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2F
> > patchwork.freedesktop.org%2Fpatch%2F217906%2F&data=02%7C01%7Cmarius
> > -cristian.vlad%40nxp.com%7Cfa1425f456fb4107c98e08d5bca75666%7C686ea
> > 1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C636622349257323713&sdata=oGyj
> > 1s15%2FZUtR0yS2FqdiPVrIJQVcx0ioyBz0fZrpAA%3D&reserved=0
> > 
> > Note, that shared-CRTC clone mode requires hardware support that
> > recent Intel display controllers do not have as far as I know.
> > 
> > Independent-CRTC clone mode is currently not supported due to
> > design
> > problems with damage tracking in libweston. Even if you could
> > configure two weston_outputs to show the same area of the desktop,
> > there would likely be problems with outdated contents on screen.
> > This
> > would be good to fix, but so far has not been a priority for
> > anyone.
> > 
> > > 
> > > *       Extended display/Tiled (Multiple displays are combined to
> > > form a single display)  
> > 
> > Weston supports extended display, but the output layout
> > configuration
> > is essentially missing. Currently you can only realize a single row
> > of outputs in an implicit order. This too would be nice to fix.
> > 
> > There is no synchronization implemented as that would require
> > kernel
> > interfaces and hardware support, either gen-lock or variable
> > refresh
> > rate.
> > 
> > > 
> > > *       Different (Different displays rendering different
> > > content)  
> > 
> > How does this differ from Extended display?
> > 
> > > 
> > > *       Portrait/Landscape orientation (this we believe is
> > > supported
> > > via configuring Weston.ini)  
> > 
> > Yes.
> > 
> > 
> > Thanks,
> > pq
> > _______________________________________________
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