[PATCH 1/6] Add weston randr protocol

Pekka Paalanen ppaalanen at gmail.com
Wed Mar 5 00:48:22 PST 2014


first, could you please try to do proper quoting in emails so we can
clearly see what you wrote and what is a quotation, for more levels
than just the most recent email. See how I do it. Thanks.

I previously bypassed the question "why", but in the below let's dig
deeped into that.

On Wed, 5 Mar 2014 05:48:33 +0000
"Wang, Quanxian" <quanxian.wang at intel.com> wrote:

> From: wayland-devel-bounces at lists.freedesktop.org
> [mailto:wayland-devel-bounces at lists.freedesktop.org] On Behalf Of
> Jasper St. Pierre Sent: Wednesday, March 05, 2014 12:51 PM To: Jason
> Ekstrand Cc: Hardening; Matthias Clasen;
> wayland-devel at lists.freedesktop.org; Pekka Paalanen; Zhang, Xiong Y;
> Wang, Quanxian Subject: Re: [PATCH 1/6] Add weston randr protocol
> I'd also say that in the automotive case, you *don't* want arbitrary
> modesetting. The user of the infotainment system in your Land Rover
> will not want to change the display resolution from 800x600 to
> 1024x768; she won't choose it from a dropdown, and it's very likely
> she doesn't know what such functionality is. [Wang, Quanxian] For
> example, someone like screen to contain more icons(big resolution)
> and someone like big icons in screen(small resolution). Resolution
> changed will be one way. I just say one way. In randr protocol, I
> don't want arbitrary. It is under the control. If security is fine,
> we could make it. If you really need it at once, just make it happen
> as a module. That is fine. Someone like 1024 or some one like 1920.
> It is different. I just provide one method for user or developer to
> choose under  their requirement. Such UIs are also fairly closely
> designed for various resolutions, with pixel-perfect graphics and so
> forth. Letting any client change the mode would be disaster, as now
> all the button sizes which were tested with various labels and font
> sizes and fingers are all different, and the rest of everything is
> chopped off! [Wang, Quanxian] I don't' see xrandr is a disaster for
> xserver. It is a useful tool. Just like in window system, I will
> change the resolution from 1024 to 1920. One thing we need to be done
> is that it is must under the control. Basically we expected wayland
> could do that. Actually we have the same goal, let right client do
> right thing. But not means we should less some function. I expected
> wayland security will be powerful.

But RandR is a disaster if random applications use it! Windows and
icons squashed into top-left corner, dialogs too large to fit on the
screen after the random application fails to restore the video mode,
or the picture just looking horrible and an average user not even
knowing why everything suddenly went ugly.

I must agree with Jasper and Jason here. What you are doing is a
dynamic compositor configuration protocol. Configuration is for system
administrators, not for the average Joe User. Furthermore, configuration
changes made this way are not permanent, not with RandrR either (which
for X is a blessing, a reboot will fix a messed up configuration). That
means if Joe the User is lucky and finds a command line snippet to do
what he wants, the setting will be gone after a reboot.

Only the technical users may want to "change the resolution", others
simply don't care as long as the picture is good. The non-technical
users probably would not know they could do that, or cannot even
imagine why they would ever want to do it.

If a graphical system wants to expose a setting like "big icons" vs.
"small icons" or whatever, they build that option into the window system
stack, which for something like automotive would include at least the
compositor, toolkits, and applications acting together to maintain the
quality of the UI. And that kind of cooperation is best done with a
specific protocol designed just for that, not a generic protocol,
because in such a stack all those programs are known in advance. On a
desktop system, such a setting is for the DE, is DE specific, and they
likely already have their own ways to communicate the settings.

Therefore it is very hard to see the benefit of a standardised
configuration protocol.

The way you are presenting this makes us assume, that you want to make
it a standard, rather than making something for your own use case and
asking for advice to make it better. This assumption colors our replies
very much.

> If some video player wants to go full-screen and all it has is a
> 800x600 surface, then let the compositor set the mode based on seeing
> that a full-screen surface has size 800x600, and we can natively set
> the mode, without the client ever communicating that it wants to do a
> mode change. [Wang, Quanxian] Yes, surface full screen mode set could
> do that. But it is only for one surface. How about others surface. It
> is really different thing. Output configuration is for all things
> happened on the output. Surface configuration is for all things
> happened on the surface. One case, if it is pixel-perfect for
> graphics like you said, why monitor or screen producer provide more
> resolutions for that? Can you expect the reason? I think fix mode
> provided will be more cheap that more. Why producer like to do that?
> from my view, it is definitely the requirement of their customers.

The hardware driver may offer several video modes just because it is
using standard drivers and components which just happen to support
multiple video modes out of the box. It would take more effort to not
expose them.

Then again, the compositor could just not expose them, in which case
the whole configuration protocol would be useless.

To me it seems that the goal, the use cases, and the target audience of
this proposal are still up in the air. I think you should re-think the
questions I gave you:
- Would you be happy with something that works for your specific use
  case only?
- Do you want to establish a universal standard, i.e. get this into
  Wayland core? If so, why?
- Do you want a sample implementation and the protocol be included in
  Weston specifically? If so, why?

The foremost, what is the use case?

"Because someone might want to change the video mode at runtime" is not
a use case, and I don't think we have yet heard a good reason why
anyone would want to do that in the way that you have proposed. That
is, why would anyone want to use the xrandr-command?

For example, if you meant this for desktop environments so that they
can implement their output management GUIs, you should first find out
if they actually need it, or if they already have a solution.

Once you are clear on the "what" and "why", we can help you with the
technical "how".

FWIW, I could see some value in dynamic configuration of Weston, the
same way as xrandr is used, to easily try new video mode settings
before writing them into the server configuration file for permanent
use. That would make it specific to Weston, and have fairly different
requirements to what we have been talking here. Trying new settings to
find a good one is very different to allowing a client do modesetting
at will. E.g. one thing that xrandr lacks AFAIK is a way to show what
you should write into the server config file to achieve the current
output setup.

On Wed, 5 Mar 2014 06:02:45 +0000
"Wang, Quanxian" <quanxian.wang at intel.com> wrote:

> [Wang, Quanxian] not only for configuration. If configuration, just
> admin or root does that. It provides the mode set including
> transform, scale as a whole for output(screen) instead of for
> surface.

Yeah, ok, but *why* would anyone use that if not only for testing new
output configurations?


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