ActiveModColor: Improve latency by caching interesting keys on layer change

Keys normally only change when switching layers, so instead of going through
every key in every cycle to look for modifiers, do that once, when layers
change (using the new `onLayerChange` event), and store the coordinates of keys
we consider modifiers in an array (currently limited to 16 items).

Then, when we want to highlight them, go over this array only, significantly
reducing the work we need to do. In a typical case, on a full-size keyboard, one
would have eight modifiers and a few layer keys, so instead of going through a
hundred keys, we go through sixteen at most, but usually considerably less.

This fixes #403, at the cost of noticeably higher PROGMEM and RAM use.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

src/kaleidoscope/plugin/LED-ActiveModColor.cpp

@@ -22,19 +22,44 @@
 namespace kaleidoscope {
 namespace plugin {
 
+uint8_t ActiveModColorEffect::mod_keys_[MAX_MODS_PER_LAYER];
+uint8_t ActiveModColorEffect::mod_key_count_;
+
 cRGB ActiveModColorEffect::highlight_color = (cRGB) {
   0xff, 0xff, 0xff
 };
 
 cRGB ActiveModColorEffect::sticky_color = CRGB(0xff, 0x00, 0x00);
 
-EventHandlerResult ActiveModColorEffect::beforeReportingState() {
+EventHandlerResult ActiveModColorEffect::onLayerChange() {
   if (!Kaleidoscope.has_leds)
     return EventHandlerResult::OK;
 
+  mod_key_count_ = 0;
+
   for (byte r = 0; r < ROWS; r++) {
     for (byte c = 0; c < COLS; c++) {
-      Key k = Layer.lookupOnActiveLayer(r, c);
+      Key k = Layer.lookup(r, c);
+
+      if (::OneShot.isOneShotKey(k) ||
+          (k.raw >= Key_LeftControl.raw && k.raw <= Key_RightGui.raw) ||
+          (k.flags == (SYNTHETIC | SWITCH_TO_KEYMAP))) {
+        uint8_t coords = r * COLS + c;
+        mod_keys_[mod_key_count_++] = coords;
+      }
+    }
+  }
+
+  return EventHandlerResult::OK;
+}
+
+EventHandlerResult ActiveModColorEffect::beforeReportingState() {
+  for (uint8_t i = 0; i < mod_key_count_; i++) {
+    uint8_t coords = mod_keys_[i];
+    byte c = coords % COLS;
+    byte r = (coords - c) / COLS;
+
+    Key k = Layer.lookup(r, c);
 
     if (::OneShot.isOneShotKey(k)) {
       if (::OneShot.isSticky(k))
@@ -59,7 +84,6 @@ EventHandlerResult ActiveModColorEffect::beforeReportingState() {
         ::LEDControl.refreshAt(r, c);
     }
   }
-  }
 
   return EventHandlerResult::OK;
 }

src/kaleidoscope/plugin/LED-ActiveModColor.h

@@ -20,6 +20,8 @@
 #include <Kaleidoscope.h>
 #include <Kaleidoscope-LEDControl.h>
 
+#define MAX_MODS_PER_LAYER 16
+
 namespace kaleidoscope {
 namespace plugin {
 class ActiveModColorEffect : public kaleidoscope::Plugin {
@@ -30,6 +32,11 @@ class ActiveModColorEffect : public kaleidoscope::Plugin {
   static cRGB sticky_color;
 
   EventHandlerResult beforeReportingState();
+  EventHandlerResult onLayerChange();
+
+ private:
+  static uint8_t mod_keys_[MAX_MODS_PER_LAYER];
+  static uint8_t mod_key_count_;
 };
 }
 }