XPLMGetAvionicsBrightnessRheo
XPLM_API float XPLMGetAvionicsBrightnessRheo(
XPLMAvionicsID inHandle);
Returns the brightness setting value, between 0 and 1, for the screen of the cockpit device with the given handle.
If the device is bound to the current aircraft, this is a shortcut to getting the brightness rheostat value from the `sim/cockpit2/switches/instrument_brightness_ratio[]` dataref; this gets the slot in the `instrument_brightness_ratio` array to which the device is bound.
If the device is not currently bound, this returns the device's own brightness rheostat value.