Brightness applet doesnt work on the desktop, fix it with "xrandr --output HDMI-1 --brightness 0.7" but no slider. ... ok lets fix that
or maybe I should just track down the source code for the brightness applet. Im currious. its just a flipping slider, but Im currious about what it actualy does, and why the heck it fails for real...
x11 dependent obviously.
Get display info:
$ xrandr
Screen 0: minimum 320 x 200, current 3840 x 2160, maximum 16384 x 16384
HDMI-1 connected primary 3840x2160+0+0 (normal left inverted right x axis y axis) 1600mm x 900mm
3840x2160 30.00*+ 25.00 24.00 29.97 23.98
4096x2160 30.00 25.00 24.00 29.97 23.98
1920x1080 60.00 50.00 59.94 30.00 25.00 24.00 29.97 23.98
...
HDMI-2 disconnected (normal left inverted right x axis y axis)
so this command, doesnt dim the TV, monitor, whatver, it dicounts the output. true dimming, backlight dimming may be a function of the interface, suchas hdmi-cec and the model of tv / monitor. The method above is to provide a means which will work, independent of specific hardware / capabilities.
#utils for cec sudo apt install cec-utils
while I learned about CEC from some previous HDMI projects, I guess CEC is possible on other modern video sources. I havent used cec-utils yet, just reading about it.
$ cec-client No device type given. Using 'recording device' CEC Parser created - libCEC version 6.0.2 no serial port given. trying autodetect: FAILED
man cec-config man cec-client both are sorta junk. but maybe the util is usable.
... is horrible. bad docs, dead projects, ... better go find that applet src... maybe in here some place. https://github.com/mate-desktop/mate-panel