How to reassign CAPSLOCK to OSX?

Question

How to reassign CAPSLOCK to OSX?

CapsLock appears to be one of the two most difficult keys to reassign (the other is the power button).

I can globally intercept NSEvent's:

_eventTap = CGEventTapCreate( kCGHIDEventTap, kCGHeadInsertEventTap, kCGEventTapOptionDefault, CGEventMaskBit( kCGEventFlagsChanged ), (CGEventTapCallBack)_tapCallback, (__bridge void *)(self)); :

However, I do not receive an event for each key up / down. This actually happens:

(CapsLock initial state is off)
Key down: NSSystemDefined: 40a00 NSSystemDefined: 40b00 (Green light is currently on)
Key: NSSystemDefined: 40b00
Key down: NSSystemDefined: 40a00 (Green light is currently off)
Key: (nothing)

Therefore, I cannot display at this level.

But I thought that I could track at a lower level using IOKit, which defines every keystroke / up event, and then eats up the CAPSLOCK events at that level (returning NULL):

 - (CGEventRef)processEvent:(CGEventRef)cgEvent { NSEvent* event = [NSEvent eventWithCGEvent:cgEvent]; NSUInteger modifiers = [event modifierFlags] & ( NSCommandKeyMask | NSAlternateKeyMask | NSShiftKeyMask | NSControlKeyMask | NSAlphaShiftKeyMask ); NSUInteger flags_changed = _modifiers ^ modifiers; if( flags_changed & NSAlphaShiftKeyMask ) { NSLog( @"Eating CAPSLOCK" ); return NULL; } _modifiers = modifiers; :

However, this does not stop CapsLock from doing its job (such as capital letters).

I even tried to remove the CapsLock modifier flag from each keyboard event inside the handler:

 if( modifiers & NSAlphaShiftKeyMask ) event = [NSEvent keyEventWithType: event.type location: NSZeroPoint modifierFlags: event.modifierFlags & ! NSAlphaShiftKeyMask timestamp: event.timestamp windowNumber: event.windowNumber context: event.context characters: event.characters charactersIgnoringModifiers: event.charactersIgnoringModifiers isARepeat: event.isARepeat keyCode: event.keyCode ];