def setup
  createCanvas(100, 100)
  background(0)
  button = createButton('Action')
  button.position(0, 0)
  button.mouseWheel do |event|
    event = Native(`event`)
    if event.deltaY > 0
      @d += 10
    else
      @d -= 10
    end
    @d = constrain(@d, 10, 100)
    @g = rand(255)
  end
  @g = 220
  @d = 50
end

def draw
  background(@g)
  ellipse(width / 2, height / 2, @d, @d)
end