avoid using global variable $beat

external_library/java/minim/drum_machine.rb

@@ -14,6 +14,7 @@ class DrumMachine < Processing::App
   java_import 'ddf.minim.ugens.Sampler'
   attr_reader :minim, :out, :kick, :snare, :hat, :bpm, :buttons
   attr_reader :kikRow, :snrRow, :hatRow
+  attr_accessor :beat
   def setup
     sketch_title 'Drum Machine'
     minim = Minim.new(self)
@@ -23,7 +24,7 @@ def setup
     @kikRow = Array.new(16, false)
     @buttons = []
     @bpm = 120
-    $beat = 0
+    @beat = 0
     # load all of our samples, using 4 voices for each.
     # this will help ensure we have enough voices to handle even
     # very fast tempos.
@@ -50,9 +51,9 @@ def draw
     # text(frameRate, width - 60, 20)
     buttons.each(&:draw)
     stroke(128)
-    ($beat % 4).zero? ? fill(200, 0, 0) : fill(0, 200, 0)
+    (beat % 4).zero? ? fill(200, 0, 0) : fill(0, 200, 0)
     # beat marker
-    rect(10 + $beat * 24, 35, 14, 9)
+    rect(10 + beat * 24, 35, 14, 9)
   end
 
   def mouse_pressed

external_library/java/minim/library/tick/lib/tick.rb

@@ -1,20 +1,21 @@
 # frozen_string_literal: true
 
 java_import 'ddf.minim.ugens.Instrument'
-
+# class Tick can access app variables by including Processing::App module
+# But we must use instance variable to set the beat
 class Tick
   include Instrument
   include Processing::Proxy
 
   def noteOn(_dur)
-    hat.trigger if hatRow[$beat]
-    snare.trigger if snrRow[$beat]
-    kick.trigger if kikRow[$beat]
+    hat.trigger if hatRow[beat]
+    snare.trigger if snrRow[beat]
+    kick.trigger if kikRow[beat]
   end
 
   def noteOff
     # next beat
-    $beat = ($beat + 1) % 16
+    Processing.app.beat = (beat + 1) % 16
     # set the new tempo
     out.setTempo(bpm)
     # play this again right now, with a sixteenth note duration