Method: Color::RGB#to_hsl

Defined in:
lib/extensions/pdf-writer/color/rgb.rb

#to_hsl ⇒ Object

Returns the HSL colour encoding of the RGB value. The conversions here are based on forumlas from www.easyrgb.com/math.php and elsewhere.



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# File 'lib/extensions/pdf-writer/color/rgb.rb', line 197

def to_hsl
  min   = [ @r, @g, @b ].min
  max   = [ @r, @g, @b ].max
  delta = (max - min).to_f

  lum   = (max + min) / 2.0

  if Color.near_zero?(delta) # close to 0.0, so it's a grey
    hue = 0
    sat = 0
  else
    if Color.near_zero_or_less?(lum - 0.5)
      sat = delta / (max + min).to_f
    else
      sat = delta / (2 - max - min).to_f
    end

    # This is based on the conversion algorithm from
    # http://en.wikipedia.org/wiki/HSV_color_space#Conversion_from_RGB_to_HSL_or_HSV
    # Contributed by Adam Johnson
    sixth = 1 / 6.0
    if @r == max # Color.near_zero_or_less?(@r - max)
      hue = (sixth * ((@g - @b) / delta))
      hue += 1.0 if @g < @b
    elsif @g == max # Color.near_zero_or_less(@g - max)
      hue = (sixth * ((@b - @r) / delta)) + (1.0 / 3.0)
    elsif @b == max # Color.near_zero_or_less?(@b - max)
      hue = (sixth * ((@r - @g) / delta)) + (2.0 / 3.0)
    end

    hue += 1 if hue < 0
    hue -= 1 if hue > 1
  end
  Color::HSL.from_fraction(hue, sat, lum)
end