objects/internal/color.go

232 lines
5.3 KiB
Go

package internal
import "fmt"
import "image/color"
// HSV represents a color with hue, saturation, and value components. Each
// component C is in range 0 <= C <= 1.
type HSV struct {
H float64
S float64
V float64
}
// HSVA is an HSV color with an added 8-bit alpha component. The alpha component
// ranges from 0x0000 (fully transparent) to 0xFFFF (opaque), and has no bearing
// on the other components.
type HSVA struct {
H float64
S float64
V float64
A uint16
}
var (
HSVModel color.Model = color.ModelFunc(hsvModel)
HSVAModel color.Model = color.ModelFunc(hsvaModel)
)
func (hsv HSV) RGBA () (r, g, b, a uint32) {
// Adapted from:
// https://www.cs.rit.edu/~ncs/color/t_convert.html
component := func (x float64) uint32 {
return uint32(float64(0xFFFF) * x)
}
s := clamp01(hsv.S)
v := clamp01(hsv.V)
if s == 0 {
light := component(v)
return light, light, light, 0xFFFF
}
h := clamp01(hsv.H) * 360
sector := int(h / 60)
// otherwise when given 1.0 for H, sector would overflow to 6
if sector > 5 { sector = 5 }
offset := (h / 60) - float64(sector)
p := component(v * (1 - s))
q := component(v * (1 - s * offset))
t := component(v * (1 - s * (1 - offset)))
va := component(v)
switch sector {
case 0: return va, t, p, 0xFFFF
case 1: return q, va, p, 0xFFFF
case 2: return p, va, t, 0xFFFF
case 3: return p, q, va, 0xFFFF
case 4: return t, p, va, 0xFFFF
default: return va, p, q, 0xFFFF
}
}
func (hsva HSVA) RGBA () (r, g, b, a uint32) {
r, g, b, a = HSV {
H: hsva.H,
S: hsva.S,
V: hsva.V,
}.RGBA()
a = uint32(hsva.A)
// alpha premultiplication
r = (r * a) / 0xFFFF
g = (g * a) / 0xFFFF
b = (b * a) / 0xFFFF
return
}
// Canon returns the color but with the H, S, and V fields are constrained to
// the range 0.0-1.0
func (hsv HSV) Canon () HSV {
hsv.H = clamp01(hsv.H)
hsv.S = clamp01(hsv.S)
hsv.V = clamp01(hsv.V)
return hsv
}
// Canon returns the color but with the H, S, and V fields are constrained to
// the range 0.0-1.0
func (hsva HSVA) Canon () HSVA {
hsva.H = clamp01(hsva.H)
hsva.S = clamp01(hsva.S)
hsva.V = clamp01(hsva.V)
return hsva
}
func clamp01 (x float64) float64 {
if x > 1.0 { return 1.0 }
if x < 0.0 { return 0.0 }
return x
}
func hsvModel (c color.Color) color.Color {
switch c := c.(type) {
case HSV: return c
case HSVA: return HSV { H: c.H, S: c.S, V: c.V }
default:
r, g, b, a := c.RGBA()
// alpha unpremultiplication
r = (r / a) * 0xFFFF
g = (g / a) * 0xFFFF
b = (b / a) * 0xFFFF
return rgbToHSV(r, g, b)
}
}
func hsvaModel (c color.Color) color.Color {
switch c := c.(type) {
case HSV: return HSVA { H: c.H, S: c.S, V: c.V, A: 0xFFFF }
case HSVA: return c
default:
r, g, b, a := c.RGBA()
hsv := rgbToHSV(r, g, b)
return HSVA {
H: hsv.H,
S: hsv.S,
V: hsv.V,
A: uint16(a),
}
}
}
func rgbToHSV (r, g, b uint32) HSV {
// Adapted from:
// https://www.cs.rit.edu/~ncs/color/t_convert.html
component := func (x uint32) float64 {
return clamp01(float64(x) / 0xFFFF)
}
cr := component(r)
cg := component(g)
cb := component(b)
var maxComponent float64
if cr > maxComponent { maxComponent = cr }
if cg > maxComponent { maxComponent = cg }
if cb > maxComponent { maxComponent = cb }
var minComponent = 1.0
if cr < minComponent { minComponent = cr }
if cg < minComponent { minComponent = cg }
if cb < minComponent { minComponent = cb }
hsv := HSV {
V: maxComponent,
}
delta := maxComponent - minComponent
if delta == 0 {
// hsva.S is undefined, so hue doesn't matter
return hsv
}
hsv.S = delta / maxComponent
switch {
case cr == maxComponent: hsv.H = (cg - cb) / delta
case cg == maxComponent: hsv.H = 2 + (cb - cr) / delta
case cb == maxComponent: hsv.H = 4 + (cr - cg) / delta
}
hsv.H *= 60
if hsv.H < 0 { hsv.H += 360 }
hsv.H /= 360
return hsv
}
// 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)
}