Mac OS X: Intercept keyboard layout change

Question

I have a problem. I have two keyboard layouts in my Mac because I have to type in two different languages while communicating with different people. I use the keyboard shortcut Cmd+Space to switch from one layout (language) to another.

I wonder if I can run custom script when Cmd+Space is pressed? I know there is an app called Punto Switcher that can do that.

My idea is to change keyboard highlighting level to indicate current language.

• Bright = German (or Russian or whatever)
• Dim = English

The question is where to find API that can

1. intercept keyboard layout in Mac OS X
2. change brightness of the keyboard highlight

Answer 1

Neat pointer to the LED brightness stuff from @Anoop Vaidya -- looks interesting!

The system sends a notification when the input method changes.

First, declare a function to receive the notification:

void theKeyboardChanged(CFNotificationCenterRef center, void *observer, CFStringRef name, const void *object, CFDictionaryRef userInfo) {
    NSLog(@"Keyboard/input method changed.");
}

Then register for the change notification:

CFNotificationCenterAddObserver(CFNotificationCenterGetDistributedCenter(),
    myContextInfo, theKeyboardChanged,
    kTISNotifySelectedKeyboardInputSourceChanged, NULL,
    CFNotificationSuspensionBehaviorDeliverImmediately);

Answer 2

I found a blog of Amit Singh, where he gave idea as in undocumented APIs , he used C, for this, you can surely find some sort of help from this.

Experimenting With Light.

Or you can try with these codes:

UInt64 lightInsideGetLEDBrightness(){
    kern_return_t kr = 0;
    IOItemCount   scalarInputCount  = 1;
    IOItemCount   scalarOutputCount = 1;
    UInt64        in_unknown = 0, out_brightness;
    kr = IOConnectCallScalarMethod(dataPort, kGetLEDBrightnessID, &in_unknown, scalarInputCount, &out_brightness, &scalarOutputCount);
    return out_brightness;
}