Basic stroke_dashed_horizontal_line to draw dashed lines/dotted lines in Prawn.

prawn_stroke_dashed_horizontal_line.rb

module Prawn::Graphics
  # E.g. stroke_dashed_horizontal_line(0, 5.cm, :at => 10.cm, :line_length => 1.cm, :space_length => 1.mm)
  # Currently rounds up line/space periods: 1 cm line length + 1 mm space as a 3 cm line would be "- - -", 3.2 cm total.
  def stroke_dashed_horizontal_line(x1,x2,options={})
    options = options.dup
    line_length = options.delete(:line_length) || 0.5.mm
    space_length = options.delete(:space_length) || line_length
    period_length = line_length + space_length
    total_length = x2 - x1

    (total_length/period_length).ceil.times do |i|
      left_bound = x1 +  i * period_length
      stroke_horizontal_line(left_bound, left_bound + line_length, options)
    end
  end
end