Remap `fn` to left mouse button on OSX - macos

Question

I get bad tendinitis from clicking the mouse all day.
In the past I used Karabiner to remap the fn key to simulate a left mouse button. However it doesn't work with Sierra.
I tried to accomplish this in Cocoa, and it correctly performs mouse-down/up when I press and release fn.
However it doesn't handle double-click / triple-click.
Also when dragging, (e.g. dragging a window, or selecting some text) nothing happens visually until I key-up, whereupon it completes.
How can I adapt my code to implement this?
First I create an event tap:
- (BOOL)tapEvents
{
_modifiers = [NSEvent modifierFlags];
if ( ! _eventTap ) {
NSLog( #"Initializing an event tap." );
// kCGHeadInsertEventTap -- new event tap should be inserted before
// any pre-existing event taps at the same location,
_eventTap = CGEventTapCreate( kCGHIDEventTap, // kCGSessionEventTap,
kCGHeadInsertEventTap,
kCGEventTapOptionDefault,
CGEventMaskBit( kCGEventKeyDown )
| CGEventMaskBit( kCGEventFlagsChanged )
| CGEventMaskBit( NSSystemDefined )
,
(CGEventTapCallBack)_tapCallback,
(__bridge void *)(self));
if ( ! _eventTap ) {
NSLog(#"unable to create event tap. must run as root or "
"add privlidges for assistive devices to this app.");
return NO;
}
}
CGEventTapEnable( _eventTap, YES );
return [self isTapActive];
}
Now I implement the callback:
CGEventRef _tapCallback(
CGEventTapProxy proxy,
CGEventType type,
CGEventRef event,
Intercept* listener
)
{
//Do not make the NSEvent here.
//NSEvent will throw an exception if we try to make an event from the tap timout type
#autoreleasepool {
if( type == kCGEventTapDisabledByTimeout ) {
NSLog(#"event tap has timed out, re-enabling tap");
[listener tapEvents];
return nil;
}
if( type != kCGEventTapDisabledByUserInput ) {
return [listener processEvent:event];
}
}
return event;
}
Finally I implement a processEvent that will pass through any event apart from fn key up/down, which will get converted to left mouse up/down:
- (CGEventRef)processEvent:(CGEventRef)cgEvent
{
//NSLog( #"- - - - - - -" );
NSEvent* event = [NSEvent eventWithCGEvent:cgEvent];
//NSLog(#"%d,%d", event.data1, event.data2);
//NSEventType type = [event type];
NSUInteger m = event.modifierFlags &
( NSCommandKeyMask | NSAlternateKeyMask | NSShiftKeyMask | NSControlKeyMask | NSAlphaShiftKeyMask | NSFunctionKeyMask );
NSUInteger flags_changed = _modifiers ^ m;
_modifiers = m;
switch( event.type ) {
case NSFlagsChanged:
{
assert(flags_changed);
//NSLog(#"NSFlagsChanged: %d, event.modifierFlags: %lx", event.keyCode, event.modifierFlags);
if( flags_changed & NSFunctionKeyMask ) {
bool isDown = _modifiers & NSFunctionKeyMask;
CGEventType evType = isDown ? kCGEventLeftMouseDown : kCGEventLeftMouseUp;
CGPoint pt = [NSEvent mouseLocation];
CGPoint mousePoint = CGPointMake(pt.x, [NSScreen mainScreen].frame.size.height - pt.y);
CGEventRef theEvent = CGEventCreateMouseEvent(NULL, evType, mousePoint, kCGMouseButtonLeft);
CGEventSetType(theEvent, evType);
CGEventPost(kCGHIDEventTap, theEvent);
CFRelease(theEvent);
//return theEvent;
}
break;
}
}
_lastEvent = [event CGEvent];
CFRetain(_lastEvent); // must retain the event. will be released by the system
return _lastEvent;
}
EDIT: Performing a double click using CGEventCreateMouseEvent()
EDIT: OSX assign left mouse click to a keyboard key

Answer 1

Karabiner now works on macOS 10.12 and later.