How to change screen brightness in Mac os x?

Question

I am working on Safari Plugin (Objective c). I want to change screen brightness from my plugin. I have tried it with "IODisplayGetFloatParameter" and "IODisplaySetFloatParameter". But it is giving me error "failed to get brightness of display 0x1b5098cc (error -536870201)". How to solve this bug?

Answer 1

Here is the answer from thread Adjust Mac display brightness Objective-C?

// almost completely from: http://mattdanger.net/2008/12/adjust-mac-os-x-display-brightness-from-the-terminal/
- (float) get_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;
        }
        return brightness;
    }       
    return -1.0;//couldn't get brightness for any display
}


// almost completely from: http://mattdanger.net/2008/12/adjust-mac-os-x-display-brightness-from-the-terminal/
- (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;
        }

        if(brightness > 0.0){
        }else{
        }
    }       

}