def setup
  background(220)
  button = createButton('Play').size(60, 30).position(20, 35)
  button.mousePressed do
    button.elt.disabled = true
    @track.play_score(score)
  end
  @track = Track.new(SQUARE, 50.0)
end

class Track
  def initialize(type, bpm = 60.0)
    @osc  = Oscillator.new(type)   # Oscillator
    @bpm  = bpm                    # beats per minute
    @time = 0.0
  end
  def play_score(score)
    score.each do |sc|
      f = sc[:f]
      v = sc[:v]
      l = sc[:l]
      @osc.start(@time).amp(v).freq(f)  # 鳴動(音量v, 周波数f)
      @time += l * (60.0 / @bpm)        # 鳴動時間
      @osc.stop(@time)                  # 鳴動時間後に停止
      @time += 0.01                     # 音同士の区切り
    end
  end
end

def score
  [
    {f: D5,  v: 0.2, l: 0.5  },
    {f: D5,  v: 0.2, l: 0.125},
    {f: E5,  v: 0.2, l: 0.125},
    {f: Fs5, v: 0.2, l: 0.25 },
    {f: Fs5, v: 0.2, l: 0.25 },
    {f: E5,  v: 0.2, l: 0.25 },
    {f: E5,  v: 0.2, l: 0.25 },
    {f: D5,  v: 0.2, l: 0.25 },
    {f: Cs5, v: 0.2, l: 0.25 },
    {f: B4,  v: 0.2, l: 0.25 },
    {f: B4,  v: 0.2, l: 0.125},
    {f: Cs5, v: 0.2, l: 0.125},
    {f: D5,  v: 0.2, l: 0.25 },
    {f: D5,  v: 0.2, l: 0.5  },
    {f: Cs5, v: 0.2, l: 0.25 },
    {f: B4,  v: 0.2, l: 0.25 },
    {f: A4,  v: 0.2, l: 1    },
  ]
end