Sass transparent color function for legacy IE (<= 8)

Sass::Script::Functions#ms_filter_rgba

module Sass::Script::Functions
	def ms_filter_rgba(*args)
		if args.size == 4
			red, green, blue, alpha = args
			return ms_rgba(rgb(red, green, blue), alpha)
		end

		if args.size != 2
			raise ArgumentError.new("wrong number of arguments (#{args.size} for 2 or 4")
		end

		color, alpha = args

		assert_type color, :Color, :color
		assert_type alpha, :Number, :alpha

		Sass::Util.check_range('Alpha channel', 0..1, alpha)

		hex = '#%02x%02x%02x%02x' % [
			alpha.value * 255,
			color.red,
			color.green,
			color.blue]
		retval = "progid:DXImageTransform.Microsoft.gradient(startColorStr='#{hex}', endColorStr='#{hex}')"

		return Sass::Script::String.new(retval)
	end
	declare :ms_filter_rgba, [:red, :green, :blue, :alpha]
	declare :ms_filter_rgba, [:color, :alpha]
end