Add Fn as a modifier key

SquirrelInputController.m

@@ -120,6 +120,13 @@ - (BOOL)handleEvent:(NSEvent*)event client:(id)sender
           release_mask = modifiers & OSX_ALT_MASK ? 0 : kReleaseMask;
           [self processKey:rime_keycode modifiers:(rime_modifiers | release_mask)];
         }
+        if (changes & OSX_FN_MASK) {
+          if (!keyCodeAvailable) {
+            rime_keycode = XK_Hyper_L;
+          }
+          release_mask = modifiers & OSX_FN_MASK ? 0 : kReleaseMask;
+          [self processKey:rime_keycode modifiers:(rime_modifiers | release_mask)];
+        }
         if (changes & OSX_COMMAND_MASK) {
           if (!keyCodeAvailable) {
             rime_keycode = XK_Super_L;
@@ -150,6 +157,11 @@ - (BOOL)handleEvent:(NSEvent*)event client:(id)sender
           modifiers & OSX_CAPITAL_MASK);
         if (rime_keycode) {
           int rime_modifiers = osx_modifiers_to_rime_modifiers(modifiers);
+          // revert non-modifier function keys' FunctionKeyMask (FwdDel, Navigations, F1..F19)
+          if ((keyCode <= 0xff && keyCode >= 0x60) || keyCode == 0x50 || keyCode == 0x4f ||
+              keyCode == 0x47 || keyCode == 0x40) {
+            rime_modifiers ^= kHyperMask;
+          }
           handled = [self processKey:rime_keycode modifiers:rime_modifiers];
           [self rimeUpdate];
         }

macos_keycode.h

@@ -9,6 +9,7 @@
 #define OSX_CTRL_MASK         1 << 18
 #define OSX_ALT_MASK          1 << 19
 #define OSX_COMMAND_MASK      1 << 20
+#define OSX_FN_MASK           1 << 23
 
 // key codes
 //

macos_keycode.m

@@ -17,6 +17,8 @@ int osx_modifiers_to_rime_modifiers(unsigned long modifiers)
     ret |= kAltMask;
   if (modifiers & OSX_COMMAND_MASK)
     ret |= kSuperMask;
+  if (modifiers & OSX_FN_MASK)
+    ret |= kHyperMask;
 
   return ret;
 }