class Magick::RVG

def dpi=(n)
  unless defined?(@dpi)
    [Float, Integer].each do |c|
      c.class_eval <<-END_DEFS, __FILE__, __LINE__ + 1
        # the default measurement - 1px is 1 pixel
        def px
          self
        end
        # inches
        def in
          self * ::Magick::RVG.dpi
        end
        # millimeters
        def mm
          self * ::Magick::RVG.dpi / 25.4
        end
        # centimeters
        def cm
          self * ::Magick::RVG.dpi / 2.54
        end
        # points
        def pt
          self * ::Magick::RVG.dpi / 72.0
        end
        # picas
        def pc
          self * ::Magick::RVG.dpi / 6.0
        end
        # percentage of the argument
        def pct(of)
          self * Float(of) / 100.0
        end
        # the default is deg
        def deg
          self
        end
        # radians -> degrees
        def rad
          self * 180.0 / Math::PI
        end
        # grads -> degrees
        def grad
          self * 9.0 / 10.0
        end
      END_DEFS
    end
  end
  @dpi = Float(n)
  @dpi
rescue ArgumentError
  raise TypeError, "Can't convert `#{n}' to Float"
end