Add an .isModifierActive method

Useful when writing an event handler that needs to check if a modifier is
active, but may run before OneShot has a chance to re-register the given
modifier.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>

README.md

@@ -94,6 +94,12 @@ modifiers and one-shot layer keys. It has the following methods:
 > useful for macros that need to fiddle with either modifier or layer state: if
 > one-shots are not active, they need not restore the original state.
 
+### `.isModifierActive(key)`
+
+> Returns if the modifier `key` has a one-shot state active. Use this together
+> with `Keyboard.isModifierActive` to catch cases where a one-shot modifier is
+> active, but not registered yet.
+
 ### `.cancel([withStickies])`
 
 > The `cancel()` method can be used to cancel any pending one-shot effects,

src/Akela/OneShot.cpp

@@ -38,7 +38,7 @@ namespace Akela {
 #define isModifier(key) (key.raw >= Key_LCtrl.raw && key.raw <= Key_RGUI.raw)
 #define isLayerKey(key) (key.flags == (KEY_FLAGS | SYNTHETIC | SWITCH_TO_KEYMAP) && key.keyCode >= MOMENTARY_OFFSET && key.keyCode <= MOMENTARY_OFFSET + 23)
 
-#define isOneShot(idx) (bitRead (State, idx))
+#define isOneShot(idx) (bitRead (State, (idx)))
 #define setOneShot(idx) (bitWrite (State, idx, 1))
 #define clearOneShot(idx) (bitWrite (State, idx, 0))
 
@@ -258,6 +258,14 @@ namespace Akela {
     return (State && !hasTimedOut () && !shouldCancel);
   }
 
+  bool
+  OneShot::isModifierActive (Key key) {
+    if (key.raw < Key_LCtrl.raw || key.raw > Key_RGUI.raw)
+      return false;
+
+    return isOneShot (key.keyCode - Key_LCtrl.keyCode);
+  }
+
   void
   OneShot::cancel (bool withStickies) {
     shouldCancel = true;

src/Akela/OneShot.h

@@ -37,6 +37,8 @@ namespace Akela {
     static void cancel (bool withStickies);
     static void cancel (void) { cancel (false); };
 
+    static bool isModifierActive (Key key);
+
     void inject (Key key, uint8_t keyState);
 
   private: