objects/internal/color.go

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package internal
2024-06-22 13:37:20 -06:00
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)
}