open.rb

require 'gruff'

g = Gruff::Line.new(400)
g.maximum_value = 100
g.minimum_value = 0
g.y_axis_increment = 5
g.theme = {
  :colors => %w(black red),
  :marker_color => 'grey',
  :font_color => 'black',
  :background_colors => 'transparent'
}

# results may vary slightly due to pseudorandomness.
real_data = (0..100).map { (1..100).count { open?(0.5) } }
g.data(:real, real_data)
g.data(:target, Array.new(100,50))
g.write('line_transparent.png')

def open?(percentage)
  rand < percentage
end