objects/internal/color.go

package internal

import "fmt"
import "image/color"

// FormatNRGBA formats an NRGBA value into a hex string.
func FormatNRGBA (nrgba color.NRGBA) string {
	return fmt.Sprintf("%02X%02X%02X%02X", nrgba.R, nrgba.G, nrgba.B, nrgba.A)
}

// ParseNRGBA parses an NRGBA value from a hex string. It can be of the format:
//   - RGB
//   - RGBA
//   - RRGGBB
//   - RRGGBBAA
// If none of these are specified, this function will return an opaque black
// color. Hex digits may either be upper case or lower case.
func ParseNRGBA (str string) color.NRGBA {
	runes := []rune(str)
	c := color.NRGBA { A: 255 }
	switch len(runes) {
	case 3:
		c.R = fillOctet(hexDigit(runes[0]))
		c.G = fillOctet(hexDigit(runes[1]))
		c.B = fillOctet(hexDigit(runes[2]))
	case 4:
		c.R = fillOctet(hexDigit(runes[0]))
		c.G = fillOctet(hexDigit(runes[1]))
		c.B = fillOctet(hexDigit(runes[2]))
		c.A = fillOctet(hexDigit(runes[3]))
	case 6:
		c.R = hexOctet(runes[0], runes[1])
		c.G = hexOctet(runes[2], runes[3])
		c.B = hexOctet(runes[4], runes[5])
	case 8:
		c.R = hexOctet(runes[0], runes[1])
		c.G = hexOctet(runes[2], runes[3])
		c.B = hexOctet(runes[4], runes[5])
		c.A = hexOctet(runes[6], runes[7])
	}
	return c
}

func hexDigit (r rune) uint8 {
	switch {
	case r >= '0' && r <= '9': return uint8(r - '0')
	case r >= 'A' && r <= 'F': return uint8(r - 'A') + 10
	case r >= 'a' && r <= 'f': return uint8(r - 'a') + 10
	default: return 0
	}
}

func fillOctet (low uint8) uint8 {
	return low << 4 | low
}

func hexOctet (high, low rune) uint8 {
	return hexDigit(high) << 4 | hexDigit(low)
}