module Kiso::ColorUtils

def contrast_text_color(hex, threshold: nil)

Returns:
  • (String) - "white" or "black"

Parameters:
  • threshold (Float, nil) -- luminance threshold override; defaults to
  • hex (String) -- a hex color string, 3-digit (#abc) or 6-digit (#aabbcc) 
def contrast_text_color(hex, threshold: nil)
  threshold ||= Kiso.config.contrast_threshold
  hex = hex.delete("#")
  hex = hex.chars.map { |c| c * 2 }.join if hex.length == 3
  r, g, b = hex.scan(/../).map { |c| c.to_i(16) / 255.0 }
  luminance = [r, g, b].map { |c|
    (c <= 0.04045) ? c / 12.92 : ((c + 0.055) / 1.055)**2.4
  }.then { |lr, lg, lb| 0.2126 * lr + 0.7152 * lg + 0.0722 * lb }
  (luminance > threshold) ? "black" : "white"
end