Add a way to optimize for a one-shot-only setup.

OneShot has a convenient way to tell us if any OneShot keys are active:
`OneShot.isActive()`. Thus, if we are using oneshots only, we can skip scanning
the whole keymap if no one-shots are active, saving us a whole lot of time per
cycle we would be spending needlessly.

The optimization is off by default, and must be turned on by the user's sketch.

Signed-off-by: Gergely Nagy <kaleidoscope@gergo.csillger.hu>

README.md

@@ -46,6 +46,15 @@ property:
 
 > The color to use for highlighting the modifiers. Defaults to a white color.
 
+### `.oneshot_only`
+
+> A flag one can set to tell the plugin that they are using one-shot modifiers
+> and layers only. This allows it to take some shortcuts, and optimize
+> performance, at the cost of not highlighting any non-oneshot keys it otherwise
+> would.
+>
+> Defaults to `false`.
+
 ## Dependencies
 
 * [Kaleidoscope-LEDControl](https://github.com/keyboardio/Kaleidoscope-LEDControl)

src/Kaleidoscope/LED-ActiveModColor.cpp

@@ -25,6 +25,7 @@ namespace kaleidoscope {
 cRGB ActiveModColorEffect::highlight_color = (cRGB) {
   0xff, 0xff, 0xff
 };
+bool ActiveModColorEffect::oneshot_only;
 
 void ActiveModColorEffect::begin(void) {
   Kaleidoscope.useLoopHook(loopHook);
@@ -34,6 +35,9 @@ void ActiveModColorEffect::loopHook(bool is_post_clear) {
   if (is_post_clear)
     return;
 
+  if (oneshot_only && !::OneShot.isActive())
+    return;
+
   for (byte r = 0; r < ROWS; r++) {
     for (byte c = 0; c < COLS; c++) {
       Key k = Layer.lookupOnActiveLayer(r, c);

src/Kaleidoscope/LED-ActiveModColor.h

@@ -29,6 +29,7 @@ class ActiveModColorEffect : public KaleidoscopePlugin {
   void begin(void) final;
 
   static cRGB highlight_color;
+  static bool oneshot_only;
 
  private:
   static void loopHook(bool is_post_clear);