Mute channel when shift + play pressed (#14)

Fixes https://github.com/awonak/alt-gravity/issues/2

Reviewed-on: https://git.pinkduck.xyz/awonak/libGravity/pulls/14

firmware/Gravity/Gravity.ino

@@ -168,6 +168,21 @@ void HandleExtClockTick() {
 //
 
 void HandlePlayPressed() {
+    // Check if SHIFT is pressed to mute all/current channel.
+    if (gravity.shift_button.On()) {
+        if (app.selected_channel == 0) {
+            // Mute all channels
+            for (int i = 0; i < Gravity::OUTPUT_COUNT; i++) {
+                app.channel[i].toggleMute();
+            }
+        } else {
+            // Mute selected channel
+            auto& ch = GetSelectedChannel();
+            ch.toggleMute();
+        }
+        return;
+    }
+
     gravity.clock.IsPaused()
         ? gravity.clock.Start()
         : gravity.clock.Stop();

firmware/Gravity/channel.h

@@ -161,6 +161,8 @@ class Channel {
     byte getSteps(bool withCvMod = false) const { return withCvMod ? pattern.GetSteps() : base_euc_steps; }
     byte getHits(bool withCvMod = false) const { return withCvMod ? pattern.GetHits() : base_euc_hits; }
 
+    void toggleMute() { mute = !mute; }
+
     /**
      * @brief Processes a clock tick and determines if the output should be high or low.
      * Note: this method is called from an ISR and must be kept as simple as possible.
@@ -168,6 +170,12 @@ class Channel {
      * @param output The output object to be modified.
      */
     void processClockTick(uint32_t tick, DigitalOutput& output) {
+        // Mute check
+        if (mute) {
+            output.Low();
+            return;
+        }
+
         const uint16_t mod_pulses = pgm_read_word_near(&CLOCK_MOD_PULSES[cvmod_clock_mod_index]);
 
         // Conditionally apply swing on down beats.
@@ -298,6 +306,9 @@ class Channel {
     // Euclidean pattern
     Pattern pattern;
 
+    // Mute channel flag
+    bool mute;
+
     // Pre-calculated pulse values for ISR performance
     uint16_t _duty_pulses;
     uint16_t _offset_pulses;