Programmatically change Mac display brightness - cocoa

Question

How to change Mac display brightness from cocoa application?

Answer 1

CGDisplayIOServicePort is deprecated in OS 10.9 – so you have to use IOServiceGetMatchingServices to get the service parameter for IODisplaySetFloatParameter. Here's a basic function that looks for services named "display" and changes their brightness.
- (void) setBrightnessTo: (float) level
{
io_iterator_t iterator;
kern_return_t result = IOServiceGetMatchingServices(kIOMasterPortDefault,
IOServiceMatching("IODisplayConnect"),
&iterator);
// If we were successful
if (result == kIOReturnSuccess)
{
io_object_t service;
while ((service = IOIteratorNext(iterator))) {
IODisplaySetFloatParameter(service, kNilOptions, CFSTR(kIODisplayBrightnessKey), level);
// Let the object go
IOObjectRelease(service);
return;
}
}
}
And in Swift (via #Dov):
private func setBrightnessLevel(level: Float) {
var iterator: io_iterator_t = 0
let result = IOServiceGetMatchingServices(kIOMasterPortDefault,
IOServiceMatching("IODisplayConnect").takeUnretainedValue(),
&iterator)
if result == kIOReturnSuccess {
var service: io_object_t = 1
for ;; {
service = IOIteratorNext(iterator)
if service == 0 {
break
}
IODisplaySetFloatParameter(service, 0, kIODisplayBrightnessKey, level)
IOObjectRelease(service)
}
}
}
(code is open source of course)

Answer 2

Expanding on Alex's answer:
In Xcode8 beta3 with Swift3, the code is a lot more streamlined.
private func setBrightness(level: Float) {
let service = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("IODisplayConnect"))
IODisplaySetFloatParameter(service, 0, kIODisplayBrightnessKey, level)
IOObjectRelease(service)
}

Answer 3

From Alec Jacobson's Brightness Menu source code:
- (void) set_brightness:(float) new_brightness {
CGDirectDisplayID display[kMaxDisplays];
CGDisplayCount numDisplays;
CGDisplayErr err;
err = CGGetActiveDisplayList(kMaxDisplays, display, &numDisplays);
if (err != CGDisplayNoErr)
printf("cannot get list of displays (error %d)\n",err);
for (CGDisplayCount i = 0; i < numDisplays; ++i) {
CGDirectDisplayID dspy = display[i];
CFDictionaryRef originalMode = CGDisplayCurrentMode(dspy);
if (originalMode == NULL)
continue;
io_service_t service = CGDisplayIOServicePort(dspy);
float brightness;
err= IODisplayGetFloatParameter(service, kNilOptions, kDisplayBrightness,
&brightness);
if (err != kIOReturnSuccess) {
fprintf(stderr,
"failed to get brightness of display 0x%x (error %d)",
(unsigned int)dspy, err);
continue;
}
err = IODisplaySetFloatParameter(service, kNilOptions, kDisplayBrightness,
new_brightness);
if (err != kIOReturnSuccess) {
fprintf(stderr,
"Failed to set brightness of display 0x%x (error %d)",
(unsigned int)dspy, err);
continue;
}
}
}

Answer 4

in Xcode 8 beta 6 does not compile:
IODisplaySetFloatParameter(service, 0, kIODisplayBrightnessKey, level)
Cannot convert value of type 'String' to expected argument type 'CFString!'
so let' cast it:
IODisplaySetFloatParameter(service, 0, kIODisplayBrightnessKey as CFString!, level)