Module: Windraw::Color

Defined in:
lib/windraw/color.rb

Overview

Parses CSS-style hex colors into straight (non-premultiplied) RGBA floats in 0.0..1.0, the form Direct2D’s D2D1::ColorF expects.

Class Method Summary collapse

Class Method Details

.parse(spec, default_alpha: 1.0) ⇒ Object

Accepts “#rgb”, “#rgba”, “#rrggbb”, “#rrggbbaa” (leading “#” optional). Returns [r, g, b, a] as floats in 0.0..1.0. Raises ArgumentError otherwise.



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# File 'lib/windraw/color.rb', line 11

def parse(spec, default_alpha: 1.0)
  unless spec.is_a?(String) || spec.respond_to?(:to_str)
    raise ArgumentError, "invalid hex color: #{spec.inspect} (expected a String)"
  end
  s = spec.to_s.strip
  s = s[1..] if s.start_with?("#")

  unless s.match?(/\A\h+\z/)
    raise ArgumentError, "invalid hex color: #{spec.inspect} (non-hex characters)"
  end

  case s.length
  when 3 # rgb
    r, g, b = s.chars.map { |c| (c * 2).to_i(16) }
    a = (default_alpha * 255).round
  when 4 # rgba
    r, g, b, a = s.chars.map { |c| (c * 2).to_i(16) }
  when 6 # rrggbb
    r, g, b = s.scan(/../).map { |h| h.to_i(16) }
    a = (default_alpha * 255).round
  when 8 # rrggbbaa
    r, g, b, a = s.scan(/../).map { |h| h.to_i(16) }
  else
    raise ArgumentError,
          "invalid hex color: #{spec.inspect} (use #rgb, #rgba, #rrggbb, or #rrggbbaa)"
  end

  [r / 255.0, g / 255.0, b / 255.0, a / 255.0]
end