Moar Powersavingz, yo.

[V!NCENT]

Hey everyone,

I just saw an option on my mobile phone regarding display settings, that I thought would benefit X.org's usability and your wallets. I have no clue what required effort would be, but I guess it would be nice for a Summer Of Code project?

What is it?
Dynamic display brightness.

What the hell does it mean?
The brightness of the screen goes up/down depending on light shining on the screen.

How does it work?
There's a front camera on my phone (that point towards whoever looks at the screen) and it checks for brightness (I think, it might also be a light sencor, but it doesn't matter) and whenever the sun is shining on my screen, my phone automatically ups the brightness.

What are the benefits?
Well, the user never has to re-adjust the brightness of the monitor.
The displayed image will always be at optimal brightness, so you can look at it when you're outside with your laptop and at night it will make sure you don't screw with your eyes.
In come cases it saves power and thus battery life of laptops.

[curaga]

Oh, you mean like with Apple laptops?

And IIRC it's already supported in linux (toggling screen brightness based on the ambient light sensor).

[whizse]

I seem to remember gnome-power-manager having support for using a webcam as an optional brightness sensor.

I think this functionality was later removed, so I guess it's one of those things that's quite hard to get working right.

[V!NCENT]

Oh, you mean like with Apple laptops?

And IIRC it's already supported in linux (toggling screen brightness based on the ambient light sensor).

Ah I see... Didn't know that. What software would I need?

[curaga]

Well, for manual changes/reading data kernel support is enough.

Then there are a couple userspace daemons for tracking the light sensor, and acting on that. I can only remember the name of one right now, pommed.

On my MBP I decided to just bind the functionality to hotkeys instead of having a daemon running.

[whizse]

This is what g-p-m was doing (for a short while):

Using the webcam is more sane that you think. Using gstreamer, the webcam is turned on for about 300ms every minute, and a picture is taken. The luminance is used to find the ambient brightness. This means we can dim the screen when walking into a dark room, and also make the screen brighter when the sun comes out of the clouds. This uses about 5mW extra power, but saves many times that if we can automatically reduce the panel brightness by 15%

http://blogs.gnome.org/hughsie/2007/05/24/backlight-brightness-fun/

g-p-m also had support for proper ambient light sensors, but that feature was disabled and later removed as it was too untested and didn't work properly on the full range of macbooks.

If you're interested in looking at how it was implemented:

http://git.gnome.org/browse/gnome-power-manager/commit/?id=c8a560caf488129c03a4e437ff7bd54f173c2f55