Re: Proposal for RandR version 1.6, Leases and EDID-based output grabs

From: Keith Packard <keithp-aN4HjG94KOLQT0dZR+AlfA@public.gmane.org>
To: Pekka Paalanen <ppaalanen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: xorg-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org,
	"Michel Dänzer" <michel-otUistvHUpPR7s880joybQ@public.gmane.org>,
	dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org
Subject: Re: Proposal for RandR version 1.6, Leases and EDID-based output grabs
Date: Wed, 03 May 2017 19:04:38 -0700	[thread overview]
Message-ID: <86tw5174y1.fsf@hiro.keithp.com> (raw)
In-Reply-To: <20170503100809.262906bb@eldfell>

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Pekka Paalanen <ppaalanen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:

> do you mean to list all kinds of display devices in the database? I was
> assuming it would list only HMDs, so not in database would imply it's a
> normal display and good for extending the desktop to.

I intended for it to be a general database to which we could add almost
anything; you can imagine using this to replace broken EDID values,
configure alternate preferred modes or whatever.

The 'desktop' boolean says whether the desktop should be expected to use
the device or not; that's all I need for the HMD case.

> Or did you mean it for exceptions? As in, define a range of HMDs, but
> the vendor put a few normal displays in the middle of the range, so one
> needs to be able to exclude those?

Oh, that's a great thought; I hadn't considered what we would do with
conflicting entries that mapped the same device. I'd like to make that
invalid, and potentially spit out a warning message somewhere...

> The reason I mentioned "virtual 2D display" was that I recall hearing
> that actually exists in some HMD hardware. If you don't do anything to
> enable a 3D mode, the HMD will process the signal to produce a virtual
> 2D display in front the user. In such case, there is no need for a VR
> compositor, the plain old 2D image signal will be shown correctly on a
> plane in the virtual space by the HMD hardware itself.

Oh, cool! That doesn't help as it means the user will want to pick if
this happens or not. Maybe just don't include it in the database and let
the VR application turn off the X output before creating a lease?

> Mind the note towards the bottom: you don't actually need a PS4 to use
> it - so it must be something built into the HMD. However, reading more
> details from
> https://blog.us.playstation.com/2016/10/03/playstation-vr-the-ultimate-faq/
> reveals that there is actually a separate processor box providing the
> cinematic mode. Sounds like it's your VR compositor as a middle-man
> hardware device rather than just a program. :-)

Interesting. I guess it's a way to make it work without hacking the
desktop environment at all?

Thanks for your suggestions; I hope we're getting closer to some kind of
prototype at least...

-- 
-keith

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