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package gfx
import (
"image"
"image/color"
"image/draw"
"math"
"math/rand"
"sort"
)
// Palette is a slice of colors.
type Palette []color.NRGBA
// Color returns the color at index n.
func (p Palette) Color(n int) color.NRGBA {
if n >= 0 && n < p.Len() {
return p[n]
}
return color.NRGBA{}
}
// Len returns the number of colors in the palette.
func (p Palette) Len() int {
return len(p)
}
// Sort palette.
func (p Palette) Sort(less func(i, j int) bool) {
sort.Slice(p, less)
}
// Random color from the palette.
func (p Palette) Random() color.NRGBA {
return p[rand.Intn(p.Len())]
}
// Tile returns a new image based on the input image, but with colors from the palette.
func (p Palette) Tile(src image.Image) *Paletted {
dst := NewPalettedImage(src.Bounds(), p)
draw.Draw(dst, dst.Bounds(), src, image.ZP, draw.Src)
return dst
}
// Convert returns the palette color closest to c in Euclidean R,G,B space.
func (p Palette) Convert(c color.Color) color.Color {
if len(p) == 0 {
return color.RGBA{}
}
return p[p.Index(c)]
}
// Index returns the index of the palette color closest to c in Euclidean
// R,G,B,A space.
func (p Palette) Index(c color.Color) int {
cr, cg, cb, ca := c.RGBA()
ret, bestSum := 0, uint32(1<<32-1)
for i, v := range p {
vr, vg, vb, va := v.RGBA()
sum := sqDiff(cr, vr) + sqDiff(cg, vg) + sqDiff(cb, vb) + sqDiff(ca, va)
if sum < bestSum {
if sum == 0 {
return i
}
ret, bestSum = i, sum
}
}
return ret
}
// AsColorPalette converts the Palette to a color.Palette.
func (p Palette) AsColorPalette() color.Palette {
var cp = make(color.Palette, len(p))
for i, c := range p {
cp[i] = c
}
return cp
}
// At returns the color at the given float64 value (range 0-1)
func (p Palette) At(t float64) color.Color {
n := len(p)
if t <= 0 || math.IsNaN(t) {
return p[0]
}
if t >= 1 {
return p[n-1]
}
i := int(math.Floor(t * float64(n-1)))
s := 1 / float64(n-1)
return LerpColors(p[i], p[i+1], (t-float64(i)*s)/s)
}
// sqDiff returns the squared-difference of x and y, shifted by 2 so that
// adding four of those won't overflow a uint32.
//
// x and y are both assumed to be in the range [0, 0xffff].
func sqDiff(x, y uint32) uint32 {
d := x - y
return (d * d) >> 2
}
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