optenter.c

// Map right-side Option to Enter in OS X
// by Henrik Nyh <http://henrik.nyh.se> 2008-03-15.
// Free to modify and redistribute with credit.
//
// The Enter key does not always do the same thing as Return: when editing
// text in Photoshop, Return breaks lines and Enter commits the changes.
// The Adium IM client and and Colloquy IRC client can be set up much the
// same way: Return breaks lines, Enter sends. The TextMate editor 
// (http://macromates.com) makes good use of Enter in its commands.
//
// For a while up until recently (2007 or so), Apple keyboards had a 
// dedicated Enter key. It has since been replaced with a right-side
// Option key. While this was probably a change for the better to most
// users, some users have gotten used to the Enter key and miss it.
// While you can still produce Enter with Fn+Return, this is not nearly
// as convenient. This app, when running, remaps right-Option to Enter.
//
// Compile like:
//   gcc -Wall -o optenter optenter.c -framework ApplicationServices 
// then just keep the app running to have right-side Option send Enter.
//
// Based on http://www.osxbook.com/book/bonus/chapter2/alterkeys/.
// http://gemma.apple.com/documentation/Carbon/Reference/QuartzEventServicesRef/Reference/reference.html
// is a good reference.
//
// Half-broken bonus feature:
// Enter is only sent if you press no other key at the same
// time; otherwise it still sends Option. So you can still e.g. use
// right-Option plus "." for ellipsis. Half-broken because you'll get
// a line break too, after you hit Option and before you hit "."
// TODO: Fix this by attaching to keyup instead? But then we'd need to
// make sure we don't send Option+Enter, and keep-pressed-for-multiples
// would become trickier.
//
// TODO: Keep app running in some nice way. Prefpane, launchd, daemon?
// TODO: Respect other modifiers, so eg Ctrl+Enter works.
// TODO: Bit logic instead of just checking integer. Necessary for "other modifiers" TODO.
// TODO: Keeping it pressed should send multiple Enters.

#include <ApplicationServices/ApplicationServices.h>

const CGKeyCode ENTER     = (CGKeyCode)76;
const CGKeyCode RIGHT_OPT = (CGKeyCode)61;
const int RIGHT_OPT_DOWN  = 524608;
const int MODIFIER_UP     = 256;

CGEventRef myCGEventCallback(CGEventTapProxy proxy, CGEventType type, CGEventRef event, void *refcon) {
        
   CGKeyCode keycode = (CGKeyCode)CGEventGetIntegerValueField(event, kCGKeyboardEventKeycode);
   CGEventFlags modifiers = CGEventGetFlags(event);
   printf("x: %i y: %i\n", kCGEventFlagMaskNumericPad, kCGEventFlagMaskAlternate);


   // Debug
   printf("Type: %i Modifiers: %i Keycode: %i\n", type, (int)modifiers, keycode);

  // Swap right-Opt for Enter
  if (modifiers == RIGHT_OPT_DOWN && keycode == RIGHT_OPT) {
    printf("swap!\n");
    CGEventRef press, release;
    press   = CGEventCreateKeyboardEvent(NULL, ENTER, true);
    release = CGEventCreateKeyboardEvent(NULL, ENTER, false);
    CGEventPost(kCGHIDEventTap, press);
    CGEventPost(kCGHIDEventTap, release);
  }

  // FIXME: Not necessary? We must return the event for it to be useful.
  return event;
}

int main(void) {
  CFMachPortRef      eventTap;
  CFRunLoopSourceRef runLoopSource;

  // Create an event tap. We are interested in modifier changes.
  CGEventFlags oldFlags =
     CGEventSourceFlagsState(kCGEventSourceStateCombinedSessionState);
  eventTap = CGEventTapCreate(kCGSessionEventTap,
                              kCGHeadInsertEventTap,
                              0,
                              CGEventMaskBit(kCGEventFlagsChanged),
                              myCGEventCallback,
                              &oldFlags);
  if (!eventTap) {
    fprintf(stderr, "failed to create event tap\n");
    exit(1);
  }

  // Create a run loop source,
  runLoopSource = CFMachPortCreateRunLoopSource(kCFAllocatorDefault, eventTap, 0);
  // add to the current run loop,
  CFRunLoopAddSource(CFRunLoopGetCurrent(), runLoopSource, kCFRunLoopCommonModes);
  // enable the event tap
  CGEventTapEnable(eventTap, true);
  // and set it all running.
  CFRunLoopRun();

  exit(0);
}