Update on screen brightness handling for Wayland

[Sebastian Kügler]

On Wednesday, August 26, 2015 09:47:11 Martin Graesslin wrote:
> at Akademy we discussed some plans on how to handle screen brightness on 
> Wayland. Unfortunately I must say that this doesn't work at all as we
> imagined 
> 
> 
> I had a look at what Weston is doing for brightness. It uses a forked 
> "libbacklight" which internally interacts with the sysfs brighness helpers.
> 
> I integrated this into KWin and tried to change backlight. But this
> obviously  did not work as only root user is allowed to write to the sysfs
> file. 

It's worse, it apparently depends on the driver, for example on the Nexus5, 
the brightness is world-readable, on my intel laptop, it's root-only.

> I then tried to open it with the logind wrapper, but logind doesn't
> have support for this kind of files, so that unfortunately doesn't work
> either.
> 
> And here, poor fool, I stand once more, no wiser than I was before. We have
> a  file only root can write to, but we are not root. Adding a KAuth helper
> to KWin would not gain us anything compared to having it in powerdevil.
> 
> So I suggest that we drop the idea that KWin is responsible for backlight
> and  move this feature completely to powerdevil and use the KAuth helper.

Sounds like the way forward.
-- 
sebas

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