OLED laptop display brightness changer

This script handles OLED display brightness settings.

the issue

With many modern laptops you're able to change the internal display brightness, by changing the "background light" via FN-key combinations. But OLED displays do not have a traditional "Background-LED" to change. That given, without proper hardware support, the FN-Keys won't change the brightness, but rather trigger some error messages like:

Precision-5540 kernel: [22999.402040] ACPI Error: [LCD_] Namespace lookup failure, AE_NOT_FOUND (20170831/psargs-364)
Precision-5540 kernel: [22999.402072] No Local Variables are initialized for Method [BRT6]
Precision-5540 kernel: [22999.402077] Initialized Arguments for Method [BRT6]:  (2 arguments defined for method invocation)
Precision-5540 kernel: [22999.402079]   Arg0:   00000000424112d7 <Obj>           Integer 0000000000000001
Precision-5540 kernel: [22999.402092]   Arg1:   0000000097f471df <Obj>           Integer 0000000000000000
Precision-5540 kernel: [22999.402107] ACPI Error: Method parse/execution failed \_SB.PCI0.PEG0.PEGP.BRT6, AE_NOT_FOUND (20170831/psparse-550)
Precision-5540 kernel: [22999.402313] ACPI Error: Method parse/execution failed \EV5, AE_NOT_FOUND (20170831/psparse-550)
Precision-5540 kernel: [22999.402510] ACPI Error: Method parse/execution failed \SMEE, AE_NOT_FOUND (20170831/psparse-550)
Precision-5540 kernel: [22999.402706] ACPI Error: Method parse/execution failed \SMIE, AE_NOT_FOUND (20170831/psparse-550)
Precision-5540 kernel: [22999.402900] ACPI Error: Method parse/execution failed \NEVT, AE_NOT_FOUND (20170831/psparse-550)
Precision-5540 kernel: [22999.403103] ACPI Error: Method parse/execution failed \_SB.PCI0.LPCB.ECDV._Q66, AE_NOT_FOUND (20170831/psparse-550)

possible workaround for OLED displays

Given that, the brightness can also be changed via xrandr:

xrandr --output eDP1 --brightness 0.3

The useful brightness values range from 0.1 to 1.0. You'll propably not use 0.0, as that might turn the screen completely black.

attaching to the FN-Keys / usage

The oled-brightness script replicates the original FN-Key behaviour. It accepts a change value as parameter, e.g. ./oled-brightness -0.1 to reduce brightness by 10% or ./oled-brightness 0.3 to raise it by 30%.

Furthermore it persists the new brightness value in the user's home directory in ~/.brightness

A call without a change value, will read the users value from ~/.brightness and set the display's brightness value accordingly.

This way you may set up your X session's key binding to call this script with a change value. And additionally call this script, without change value, at session start to reset it to the last value. (Unfortunately the X session will likely restart at 1.0 again otherwise.)

requirements - or - why PHP?

• any available php-cli interpreter
• xrandr

Well mostly, because

• Bash can't handle float values, without jumping some "dirty" loops.
• Zsh might be a hurdle to the unexperienced users.
• php was ... nah, that hammer was in reach.

I'll propably supply a zsh version later on.