D13095: Scren brightness follow a quatratic progression

[Roman Gilg]

romangg added a comment.


  Please create a table with what would happen when. To me it sounds like 
something would not work out in the end, but I can be wrong.

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: kjslag, sharvey, zzag, ngraham, romangg, plasma-devel, LeGast00n, 
ericadams, jraleigh, GB_2, ragreen, Pitel, ZrenBot, himcesjf, lesliezhai, 
ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Nathaniel Graham]

ngraham added a comment.


  In D13095#473975 , @kjslag wrote:
  
  > > Well it's not me that matters; it's all the other people with weird 
screens like mine, as well as the prople whose screens don't do this. We need 
to wither come up with a solution that works for everyone, or else mark some 
class of screen as misconfigured so we can tell those people to file kernel 
bugs.
  >
  > My goal was to propose a solution that should work for everyone. For your 
laptop and the solution I proposed, the lowest brightness would still turn off 
the backlight, and the next brightness would turn it on, just as it currently 
does. For screens like mine where only brightness=0 turns off the display, the 
solution I proposed would never turn off the backlight. In both cases, it 
doesn't seem like there would be a regression.
  
  
  All right, sounds good enough to me!

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: kjslag, sharvey, zzag, ngraham, romangg, plasma-devel, LeGast00n, 
ericadams, jraleigh, GB_2, ragreen, Pitel, ZrenBot, himcesjf, lesliezhai, 
ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Kevin Slagle]

kjslag added a comment.


  > Well it's not me that matters; it's all the other people with weird screens 
like mine, as well as the prople whose screens don't do this. We need to wither 
come up with a solution that works for everyone, or else mark some class of 
screen as misconfigured so we can tell those people to file kernel bugs.
  
  My goal was to propose a solution that should work for everyone. For your 
laptop and the solution I proposed, the lowest brightness would still turn off 
the backlight, and the next brightness would turn it on, just as it currently 
does. For screens like mine where only brightness=0 turns off the display, the 
solution I proposed would never turn off the backlight. In both cases, it 
doesn't seem like there would be a regression.

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: kjslag, sharvey, zzag, ngraham, romangg, plasma-devel, LeGast00n, 
ericadams, jraleigh, GB_2, ragreen, Pitel, ZrenBot, himcesjf, lesliezhai, 
ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Nathaniel Graham]

ngraham added a comment.


  In D13095#472946 , @kjslag wrote:
  
  > In D13095#467997 , @ngraham 
wrote:
  >
  > > Moving the brightness to zero is supposed to turn the //backlight// off, 
not the //screen// right?
  >
  >
  > I don't see why. It seems better to put the screen into a low energy mode 
than to just turn off the backlight in order to save more watts. It also seems 
strange for the brightness slider to go all the way down to zero brightness. Do 
any other desktop environments or operating systems do that?
  
  
  On macOS, it turns the backlight off but keeps the screen on. But yeah, I can 
see how this isn't exactly very useful. I think I'm okay with the bottom level 
turning off the screen entirely.
  
  > In D13095#467733 , @kjslag wrote:
  > 
  >> In order to deal with Nate's problem, perhaps instead of starting with 
brightness=0, we could just start with the next increment of brightness, which 
happens to be 2 for Nate. Nate's situation would be similar to before the patch 
was applied: only the lowest brightness setting turns off his screen. So there 
wouldn't be a regression for Nate.
  > 
  > 
  > Are there still any objections to this solution?
  
  Well it's not me that matters; it's all the other people with weird screens 
like mine, as well as the prople whose screens don't do this. We need to wither 
come up with a solution that works for everyone, or else mark some class of 
screen as misconfigured so we can tell those people to file kernel bugs.

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: kjslag, sharvey, zzag, ngraham, romangg, plasma-devel, ericadams, jraleigh, 
GB_2, ragreen, Pitel, ZrenBot, himcesjf, lesliezhai, ali-mohamed, 
jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Kevin Slagle]

kjslag added a comment.


  In D13095#467997 , @ngraham wrote:
  
  > Moving the brightness to zero is supposed to turn the //backlight// off, 
not the //screen// right?
  
  
  I don't see why. It seems better to put the screen into a low energy mode 
than to just turn off the backlight in order to save more watts. It also seems 
strange for the brightness slider to go all the way down to zero brightness. Do 
any other desktop environments or operating systems do that?
  
  In D13095#467733 , @kjslag wrote:
  
  > In order to deal with Nate's problem, perhaps instead of starting with 
brightness=0, we could just start with the next increment of brightness, which 
happens to be 2 for Nate. Nate's situation would be similar to before the patch 
was applied: only the lowest brightness setting turns off his screen. So there 
wouldn't be a regression for Nate.
  
  
  Are there still any objections to this solution?

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: kjslag, sharvey, zzag, ngraham, romangg, plasma-devel, jraleigh, GB_2, 
ragreen, Pitel, ZrenBot, himcesjf, lesliezhai, ali-mohamed, jensreuterberg, 
abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Nathaniel Graham]

ngraham added a comment.


  In D13095#467779 , @romangg wrote:
  
  > In D13095#279659 , @thsurrel 
wrote:
  >
  > > - accept to break some systems (but who wants that ?)
  >
  >
  > If these systems' breakage is because of an erroneous kernel driver, we can 
accept it. My system goes with brightness from 0 to 7500, and screen is 
activated at 1. It going dark at some higher value than 0 seems buggy to me. Is 
there some kernel directive on how it is supposed to work, i.e. if a display 
should be on at 1? @ngraham: what laptop model do you have?
  
  
  HP Spectre x360, late 2016 model

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: kjslag, sharvey, zzag, ngraham, romangg, plasma-devel, jraleigh, GB_2, 
ragreen, Pitel, ZrenBot, himcesjf, lesliezhai, ali-mohamed, jensreuterberg, 
abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Nathaniel Graham]

ngraham added a comment.


  Moving the brightness to zero is supposed to turn the //backlight// off, not 
the //screen// right?

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: kjslag, sharvey, zzag, ngraham, romangg, plasma-devel, jraleigh, GB_2, 
ragreen, Pitel, ZrenBot, himcesjf, lesliezhai, ali-mohamed, jensreuterberg, 
abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Kevin Slagle]

kjslag added a comment.


  @romangg The current code selects from a discrete set of brightness levels 
which starts at zero. I was suggesting just removing the zero brightness level 
and using the next level as the minimum brightness level.
  
  I didn't realize turning off the screen at the lowest brightness level was an 
intended feature. My past 3 laptops didn't do that, and I've never seen a 
laptop do that on any operating system. It seems like an unintuitive feature 
and could confuse someone who doesn't realize that their screen is black 
because the brightness is all the way down. Perhaps it would be better to add a 
different hotkey for this function. (That's what I did.)
  
  Also note that setting brightness=0 probably isn't a power efficient way to 
turn the screen off. My laptop uses 4W less energy when I turn the screen off 
with
  xset dpms force off
  than when I set brightness=0.

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: kjslag, sharvey, zzag, ngraham, romangg, plasma-devel, jraleigh, GB_2, 
ragreen, Pitel, ZrenBot, himcesjf, lesliezhai, ali-mohamed, jensreuterberg, 
abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Roman Gilg]

romangg added a comment.


  In D13095#279659 , @thsurrel wrote:
  
  > - accept to break some systems (but who wants that ?)
  
  
  If these systems' breakage is because of an erroneous kernel driver, we can 
accept it. My system goes with brightness from 0 to 7500, and screen is 
activated at 1. It going dark at some higher value than 0 seems buggy to me. Is 
there some kernel directive on how it is supposed to work, i.e. if a display 
should be on at 1? @ngraham: what laptop model do you have?

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: kjslag, sharvey, zzag, ngraham, romangg, plasma-devel, jraleigh, GB_2, 
ragreen, Pitel, ZrenBot, himcesjf, lesliezhai, ali-mohamed, jensreuterberg, 
abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Kevin Slagle]

kjslag added a comment.


  I like the idea of this patch. I just reassigned my brightness hotkeys to a 
small script that does almost exactly what this patch does before I discovered 
this patch.
  
  In order to deal with Nate's problem, perhaps instead of starting with 
brightness=0, we could just start with the next increment of brightness, which 
happens to be 2 for Nate. Nate's situation would be similar to before the patch 
was applied: only the lowest brightness setting turns off his screen. So there 
wouldn't be a regression for Nate.
  
  On my laptop, brightness=0 turns the screen off and brightness 1 through 46 
correspond to the minimum brightness, and max_brightness=24242. My proposal 
would also be better for me since then my screen wouldn't turn off with the 
minimum brightness.

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: kjslag, sharvey, zzag, ngraham, romangg, plasma-devel, jraleigh, GB_2, 
ragreen, Pitel, ZrenBot, himcesjf, lesliezhai, ali-mohamed, jensreuterberg, 
abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Scott Harvey]

sharvey added a comment.


  A couple of random ideas:
  
  - The Arch Wiki has a lengthy page 
 on screen brightness. Maybe 
there's something there that can help.
  - Is there a valid use case for going all the way to zero? Minimum doesn't 
necessarily need to equal "off". If it's an external screen, it's got a power 
button. The only complex situation I can imagine is a laptop + monitor dual 
screen setup. Thoughts?
  - Perhaps, when starting from zero, move two steps instead of just one. That 
would fix the "Nate Problem", and i doubt anyone would say "okay, my screen is 
really dim, but I wanted it even dimmer."

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: sharvey, zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, 
lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Nathaniel Graham]

ngraham added a comment.


  I don't think we want the possibility of breaking anyone. A setting doesn't 
seem ideal either; who would ever find and change this?
  
  Rather, let's focus on the issue that's hurting us here to see if we can 
resolve it somehow. Is there any way to programmatically detect the minimum 
brightness before the backlight turns off? Or could it be a kernel bug that 
there are ever any non-zero brightness values that still have the backlight off?

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: sharvey, zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, 
lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Thomas Surrel]

thsurrel added a comment.


  > Same values as `/sys/class/backlight/*/brightness`, in other words.
  
  Thanks Nate, even if that's not the answer I was hoping for ...
  The future of this patch:
  
  - accept to break some systems (but who wants that ?)
  - add an option for this quadratic progression somehwere
  - drop it
  
  What do you think ? (the question is for anybody interested!)

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: sharvey, zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, 
lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Nathaniel Graham]

ngraham added a comment.


Lowest setting:
$ cat /sys/class/backlight/intel_backlight/actual_brightness 
0
Next setting:
$ cat /sys/class/backlight/intel_backlight/actual_brightness 
2
  
  Same values as `/sys/class/backlight/*/brightness`, in other words.

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: sharvey, zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, 
lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Scott Harvey]

sharvey added a comment.


  It seems I have some system rebuilding to do first. I'm not up for tackling 
it tonight. I'll work on it in the morning and try to get you some more data.

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: sharvey, zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, 
lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Scott Harvey]

sharvey added a comment.


  In D13095#277963 , @thsurrel wrote:
  
  > Hi Scott, thanks for the help!
  >  If you can apply the patch, we could see if you have the same behavior 
than Nate with his hardware: when setting a very low value (for him, it's in 
the range 1 to 5) to /sys/class/backlight//brightness his screen does 
not turn on at all. I would like to know if 
/sys/class/backlight//actual_brightness is then saying something 
different than /sys/class/backlight//brightness.
  >  On my computer the backlight goes on as soon as I put 1 to 
/sys/class/backlight//brightness, so I cannot reproduce this.
  >  I hope I'm clear enough :)
  
  
  Makes sense. I'll get it patched and repost in a couple of hours.
  
  FYI: this where a remote control app like NoMachine comes in handy - you can 
issue commands on your tablet (or phone!) and watch what happens on the big 
screen.

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: sharvey, zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, 
lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Thomas Surrel]

thsurrel added a comment.


  Hi Scott, thanks for the help!
  If you can apply the patch, we could see if you have the same behavior than 
Nate with his hardware: when setting a very low value (for him, it's in the 
range 1 to 5) to /sys/class/backlight//brightness his screen does not 
turn on at all. I would like to know if 
/sys/class/backlight//actual_brightness is then saying something 
different than /sys/class/backlight//brightness.
  On my computer the backlight goes on as soon as I put 1 to 
/sys/class/backlight//brightness, so I cannot reproduce this.
  I hope I'm clear enough :)

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: sharvey, zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, 
lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Scott Harvey]

sharvey added a comment.


  Hope you don't mind me jumping in - I'm another one of Nate's protegees... 
here's some data for you. These values are before your patch. Let me know if 
you'd like me to apply your patch and redo the testing.
  
0 (lowest)
75 (backlight on)
150
225
300
375
450
525
600
675
750
825
900
975
1050
1125
1200
1275
1350
1425
1500 (highest)
  
  1500 matches what's in the `mac_brightness` file.

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: sharvey, zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, 
lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Thomas Surrel]

thsurrel added a comment.


  Hi Nate, sorry I'm asking you one more thing before giving up on this patch 
(even though I find it really useful for my personal use).
  When your screen is off, with a brightness value of 4 for example, could you 
tell me what is the value reported in /sys/class/backlight//actual_brightness ?

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, lesliezhai, 
ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Nathaniel Graham]

ngraham added a comment.


  My backlight turns on at 6. It's off at 5.

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, lesliezhai, 
ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Thomas Surrel]

thsurrel added a comment.


  Thanks Nate. If your screen does not turn on while passing from 0 to 2, than 
this patch is in trouble ...
  Could you tell me at what value your screen does turn on for the first time, 
starting from 0 (by writing values directly in /sys/class/backlight//brightness) ?

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, lesliezhai, 
ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Nathaniel Graham]

ngraham added a comment.


  Max brightness: 937
  
  Individual brightness levels per key-press:
  
0 (lowest setting)
2
9
21
37
59
84
115
150
190
234
283
337
396
459
527
600
677
759
846
937 (highest setting)

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, lesliezhai, 
ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Thomas Surrel]

thsurrel added a comment.


  Could you provide the value of the system brightness after each key press 
(cat /sys/class/backlight/*/brightness) as well as the maximun brightness of 
your hardware (cat /sys/class/backlight/*/max_brightness) ?
  I know, I'm asking you to work with a black screen ...

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, lesliezhai, 
ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Vlad Zagorodniy]

zzag added inline comments.

INLINE COMMENTS

> powerdevilbrightnesslogic.cpp:135
> +return value * 100.0 / m_valueMax;
> +} else {
> +return valueToStep(value) * 100.0 / m_steps;

Coding style nitpick: don't use "else" after a return statement. Same down 
below.

Kdelibs/Frameworks coding style doesn't say anything about early returns so 
here are links to other coding styles

- https://releases.llvm.org/2.7/docs/CodingStandards.html#hl_else_after_return
- 
https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Coding_Style#General_C.2FC.2B.2B_Practices
 (the first item)
- https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md 
(see Code Formatting section)

- 
https://clang.llvm.org/extra/clang-tidy/checks/readability-else-after-return.html

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel, #plasma, broulik, ngraham
Cc: zzag, ngraham, romangg, plasma-devel, ragreen, Pitel, ZrenBot, lesliezhai, 
ali-mohamed, jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Thomas Surrel]

thsurrel updated this revision to Diff 34825.
thsurrel added a reviewer: Plasma.
thsurrel added a comment.


  Added context

REPOSITORY
  R122 Powerdevil

CHANGES SINCE LAST UPDATE
  https://phabricator.kde.org/D13095?vs=34812=34825

REVISION DETAIL
  https://phabricator.kde.org/D13095

AFFECTED FILES
  daemon/actions/bundled/brightnesscontrol.cpp
  daemon/powerdevilbackendinterface.cpp
  daemon/powerdevilbackendinterface.h
  daemon/powerdevilbrightnesslogic.cpp

To: thsurrel, #plasma
Cc: romangg, plasma-devel, ragreen, Pitel, ZrenBot, lesliezhai, ali-mohamed, 
jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Roman Gilg]

romangg added a comment.


  Pls add context and reviewer Plasma.

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

To: thsurrel
Cc: romangg, plasma-devel, ragreen, Pitel, ZrenBot, lesliezhai, ali-mohamed, 
jensreuterberg, abetts, sebas, apol, mart

D13095: Scren brightness follow a quatratic progression

[Thomas Surrel]

thsurrel created this revision.
Restricted Application added a project: Plasma.
Restricted Application added a subscriber: plasma-devel.
thsurrel requested review of this revision.

REVISION SUMMARY
  Modern hardware allow to adjust the screen brightness very precisely,
  with more than hundreds or thousands different possible levels. When
  modifying the screen brightness through the keyboard shortcuts, we
  are not making the best use of this very fine grain possibility,
  notably when in low light conditions. As of today, the progression
  is linear, so for a maximum brightness level of 1000 we are making
  20 steps of 50. This is not great since jumping from 0 to 50 can be
  already too bright when using a laptop in the dark. And when in full
  light, going from 950 to 1000 is barely noticeable.
  
  This patch tries to improve the situation by switching from a
  linear to a quadratic progression, offering smaller steps in the
  low level brightness.
  
  The switch to the quadratic progression is done in
  powerdevilbrightnesslogic.cpp, the other modifications ensure that
  the OSD still displays equal steps when giving a visual feedback,
  otherwise the lower steps are barely distinguishible.
  
  BUG: 362830

REPOSITORY
  R122 Powerdevil

REVISION DETAIL
  https://phabricator.kde.org/D13095

AFFECTED FILES
  daemon/actions/bundled/brightnesscontrol.cpp
  daemon/powerdevilbackendinterface.cpp
  daemon/powerdevilbackendinterface.h
  daemon/powerdevilbrightnesslogic.cpp

To: thsurrel
Cc: plasma-devel, ragreen, Pitel, ZrenBot, lesliezhai, ali-mohamed, 
jensreuterberg, abetts, sebas, apol, mart