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// +build !tinygo
package gfx
import (
"image/color"
"math"
)
// SortByHue sorts based on (HSV) Hue.
func (p Palette) SortByHue() {
p.Sort(func(i, j int) bool {
return ColorToHSV(p[i]).Hue > ColorToHSV(p[i]).Hue
})
}
// ColorToHSV converts a color into HSV.
func ColorToHSV(c color.Color) HSV {
var (
r, g, b = floatRGB(c)
min, max = minRGB(r, g, b), maxRGB(r, g, b)
h, s, v, d = max, max, max, max - min
)
if max == 0 {
s = 0
} else {
s = d / max
}
if max == min {
h = 0 // achromatic
} else {
switch max {
case r:
if g < b {
h = (g-b)/d + 6.0
} else {
h = (g - b) / d
}
case g:
h = (b-r)/d + 2.0
case b:
h = (r-g)/d + 4.0
}
}
return HSV{h, s * 100.0, v * 100.0}
}
// HSV is the hue, saturation and value color representation.
// - Hue [0,360]
// - Saturation [0,1]
// - Value [0,1]
type HSV struct {
Hue float64
Saturation float64
Value float64
}
// Components in HSV.
func (hsv HSV) Components() (h, s, v float64) {
return hsv.Hue, hsv.Saturation, hsv.Value
}
// RGBA converts a HSV color value to color.RGBA.
func (hsv HSV) RGBA() color.RGBA {
h, s, v := hsv.Components()
hprime := h / 60.0
var r, g, b float64
c := v * s
x := c * math.Abs(math.Remainder(hprime, 2))
m := v - c
switch {
case hprime >= 0 && hprime < 1:
r = c
g = x
b = 0
case hprime >= 1 && hprime < 2:
r = x
g = c
b = 0
case hprime >= 2 && hprime < 3:
r = 0
g = c
b = x
case hprime >= 3 && hprime < 4:
r = 0
g = x
b = c
case hprime >= 4 && hprime < 5:
r = x
g = 0
b = c
case hprime >= 5 && hprime < 6:
r = c
g = 0
b = x
}
return ColorRGBA(
uint8(math.Round((r+m)*255)),
uint8(math.Round((g+m)*255)),
uint8(math.Round((b+m)*255)),
255,
)
}
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