This allows to control the backlight level on certain Intel(R) GPUs,
including i915.

This has been taken from intel-gpu-tools which can be found
here: http://cgit.freedesktop.org/xorg/app/intel-gpu-tools/

This is a fork of https://github.com/grembo/intel_backlight_fbsd.

Build:
  pkg install git libdrm libpciaccess
  git clone https://github.com/maurizio-emmex/intel_backlight_fbsd
  cd intel_backlight_fbsd
  make install
(this installs intel_backlight setuid root, so any user can execute it).

Usage:
  $ intel_backlight
  current backlight value: 30% (281/937)
  $ intel_backlight 50
  current backlight value: 15% (141/937)
  set backlight to 50% (469/937)
  $ intel_backlight incr
  current backlight value: 50% (469/937)
  set backlight to 51% (478/937)
  $ intel_backlight incr
  current backlight value: 51% (478/937)
  set backlight to 60% (562/937)
  $ intel_backlight incr
  current backlight value: 60% (562/937)
  set backlight to 70% (656/937)
  $ intel_backlight decr
  current backlight value: 70% (656/937)
  set backlight to 60% (562/937)
  $ intel_backlight decr
  current backlight value: 60% (562/937)
  set backlight to 51% (478/937)

Also you can:
# pkg install xbindkeys
and add/create in ~/.xbindkeysrc
"intel_backlight decr"
        control+shift + F2
"intel_backlight incr"
        control+shift + F3
Then you can just use Ctrl+Shift+F2/F3 for this, for example, as they are
labeled with the symbols of up/down brightness in the Samsung Ativ Book2 laptop. 

The included example allows adjusting brightness automatically based on the
input of the isl driver (currently not part of standard FreeBSD).

Usage:
  ./isl_backlight.sh &