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colette.go
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colette.go
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// Convert between truecolor, xterm(1) 256 color and 16 color.
// Single-header library.
// Arranged from [tmux].
//
// [tmux]: https://github.com/tmux/tmux
package colette
// RgbTo256 converts an RGB triplet to the xterm(1) 256 color palette.
//
// xterm provides a 6x6x6 color cube (16 - 231) and 24 greys (232 - 255). We
// map our RGB color to the closest in the cube, also work out the closest
// grey, and use the nearest of the two.
//
// Note that the xterm has much lower resolution for darker colors (they are
// not evenly spread out), so our 6 levels are not evenly spread: 0x0, 0x5f
// (95), 0x87 (135), 0xaf (175), 0xd7 (215) and 0xff (255). Greys are more
// evenly spread (8, 18, 28 ... 238).
func RgbTo256(r, g, b byte) int {
q2c := []int{0x00, 0x5f, 0x87, 0xaf, 0xd7, 0xff}
ir := int(r)
ig := int(g)
ib := int(b)
var qr, qg, qb, cr, cg, cb, idx, greyAvg, greyIdx, grey int
/* Map RGB to 6x6x6 cube. */
qr = colorTo6cube(ir)
cr = q2c[qr]
qg = colorTo6cube(ig)
cg = q2c[qg]
qb = colorTo6cube(ib)
cb = q2c[qb]
/* If we have hit the color exactly, return early. */
if cr == ir && cg == ig && cb == ib {
return 16 + 36 * qr + 6 * qg + qb
}
/* Work out the closest grey (average of RGB). */
greyAvg = (ir + ig + ib) / 3
if greyAvg > 238 {
greyIdx = 23
} else {
greyIdx = (greyAvg - 3) / 10
}
grey = 8 + (10 * greyIdx)
/* Is grey or 6x6x6 color closest? */
if distSq(grey, grey, grey, ir, ig, ib) < distSq(cr, cg, cb, ir, ig, ib) {
idx = 232 + greyIdx
} else {
idx = 16 + 36*qr + 6*qg + qb
}
return idx
}
// JoinRgb joins RGB into a color.
func JoinRgb(r, g, b byte) int {
return int(r)<<16 | int(g)<<8 | int(b)
}
// SplitRgb converts 256 color to RGB color.
func SplitRgb(c int) (r, g, b byte) {
return byte(c >> 16), byte(c >> 8), byte(c)
}
// Color256ToRgb converts 256 color to RGB color.
func Color256ToRgb(c byte) int {
return color256ToRgbTable[c]
}
// Color256To16 converts 256 color to 16 color.
func Color256To16(c byte) byte {
return color256To16Table[c]
}
func distSq(R, G, B, r, g, b int) int {
return (R-r)*(R-r) + (G-g)*(G-g) + (B-b)*(B-b)
}
func colorTo6cube(v int) int {
if v < 48 {
return 0
}
if v < 114 {
return 1
}
return (v - 35) / 40
}
var (
color256ToRgbTable = []int{
0x000000, 0x800000, 0x008000, 0x808000,
0x000080, 0x800080, 0x008080, 0xc0c0c0,
0x808080, 0xff0000, 0x00ff00, 0xffff00,
0x0000ff, 0xff00ff, 0x00ffff, 0xffffff,
0x000000, 0x00005f, 0x000087, 0x0000af,
0x0000d7, 0x0000ff, 0x005f00, 0x005f5f,
0x005f87, 0x005faf, 0x005fd7, 0x005fff,
0x008700, 0x00875f, 0x008787, 0x0087af,
0x0087d7, 0x0087ff, 0x00af00, 0x00af5f,
0x00af87, 0x00afaf, 0x00afd7, 0x00afff,
0x00d700, 0x00d75f, 0x00d787, 0x00d7af,
0x00d7d7, 0x00d7ff, 0x00ff00, 0x00ff5f,
0x00ff87, 0x00ffaf, 0x00ffd7, 0x00ffff,
0x5f0000, 0x5f005f, 0x5f0087, 0x5f00af,
0x5f00d7, 0x5f00ff, 0x5f5f00, 0x5f5f5f,
0x5f5f87, 0x5f5faf, 0x5f5fd7, 0x5f5fff,
0x5f8700, 0x5f875f, 0x5f8787, 0x5f87af,
0x5f87d7, 0x5f87ff, 0x5faf00, 0x5faf5f,
0x5faf87, 0x5fafaf, 0x5fafd7, 0x5fafff,
0x5fd700, 0x5fd75f, 0x5fd787, 0x5fd7af,
0x5fd7d7, 0x5fd7ff, 0x5fff00, 0x5fff5f,
0x5fff87, 0x5fffaf, 0x5fffd7, 0x5fffff,
0x870000, 0x87005f, 0x870087, 0x8700af,
0x8700d7, 0x8700ff, 0x875f00, 0x875f5f,
0x875f87, 0x875faf, 0x875fd7, 0x875fff,
0x878700, 0x87875f, 0x878787, 0x8787af,
0x8787d7, 0x8787ff, 0x87af00, 0x87af5f,
0x87af87, 0x87afaf, 0x87afd7, 0x87afff,
0x87d700, 0x87d75f, 0x87d787, 0x87d7af,
0x87d7d7, 0x87d7ff, 0x87ff00, 0x87ff5f,
0x87ff87, 0x87ffaf, 0x87ffd7, 0x87ffff,
0xaf0000, 0xaf005f, 0xaf0087, 0xaf00af,
0xaf00d7, 0xaf00ff, 0xaf5f00, 0xaf5f5f,
0xaf5f87, 0xaf5faf, 0xaf5fd7, 0xaf5fff,
0xaf8700, 0xaf875f, 0xaf8787, 0xaf87af,
0xaf87d7, 0xaf87ff, 0xafaf00, 0xafaf5f,
0xafaf87, 0xafafaf, 0xafafd7, 0xafafff,
0xafd700, 0xafd75f, 0xafd787, 0xafd7af,
0xafd7d7, 0xafd7ff, 0xafff00, 0xafff5f,
0xafff87, 0xafffaf, 0xafffd7, 0xafffff,
0xd70000, 0xd7005f, 0xd70087, 0xd700af,
0xd700d7, 0xd700ff, 0xd75f00, 0xd75f5f,
0xd75f87, 0xd75faf, 0xd75fd7, 0xd75fff,
0xd78700, 0xd7875f, 0xd78787, 0xd787af,
0xd787d7, 0xd787ff, 0xd7af00, 0xd7af5f,
0xd7af87, 0xd7afaf, 0xd7afd7, 0xd7afff,
0xd7d700, 0xd7d75f, 0xd7d787, 0xd7d7af,
0xd7d7d7, 0xd7d7ff, 0xd7ff00, 0xd7ff5f,
0xd7ff87, 0xd7ffaf, 0xd7ffd7, 0xd7ffff,
0xff0000, 0xff005f, 0xff0087, 0xff00af,
0xff00d7, 0xff00ff, 0xff5f00, 0xff5f5f,
0xff5f87, 0xff5faf, 0xff5fd7, 0xff5fff,
0xff8700, 0xff875f, 0xff8787, 0xff87af,
0xff87d7, 0xff87ff, 0xffaf00, 0xffaf5f,
0xffaf87, 0xffafaf, 0xffafd7, 0xffafff,
0xffd700, 0xffd75f, 0xffd787, 0xffd7af,
0xffd7d7, 0xffd7ff, 0xffff00, 0xffff5f,
0xffff87, 0xffffaf, 0xffffd7, 0xffffff,
0x080808, 0x121212, 0x1c1c1c, 0x262626,
0x303030, 0x3a3a3a, 0x444444, 0x4e4e4e,
0x585858, 0x626262, 0x6c6c6c, 0x767676,
0x808080, 0x8a8a8a, 0x949494, 0x9e9e9e,
0xa8a8a8, 0xb2b2b2, 0xbcbcbc, 0xc6c6c6,
0xd0d0d0, 0xdadada, 0xe4e4e4, 0xeeeeee,
}
color256To16Table = []byte{
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
0, 4, 4, 4, 12, 12, 2, 6, 4, 4, 12, 12, 2, 2, 6, 4,
12, 12, 2, 2, 2, 6, 12, 12, 10, 10, 10, 10, 14, 12, 10, 10,
10, 10, 10, 14, 1, 5, 4, 4, 12, 12, 3, 8, 4, 4, 12, 12,
2, 2, 6, 4, 12, 12, 2, 2, 2, 6, 12, 12, 10, 10, 10, 10,
14, 12, 10, 10, 10, 10, 10, 14, 1, 1, 5, 4, 12, 12, 1, 1,
5, 4, 12, 12, 3, 3, 8, 4, 12, 12, 2, 2, 2, 6, 12, 12,
10, 10, 10, 10, 14, 12, 10, 10, 10, 10, 10, 14, 1, 1, 1, 5,
12, 12, 1, 1, 1, 5, 12, 12, 1, 1, 1, 5, 12, 12, 3, 3,
3, 7, 12, 12, 10, 10, 10, 10, 14, 12, 10, 10, 10, 10, 10, 14,
9, 9, 9, 9, 13, 12, 9, 9, 9, 9, 13, 12, 9, 9, 9, 9,
13, 12, 9, 9, 9, 9, 13, 12, 11, 11, 11, 11, 7, 12, 10, 10,
10, 10, 10, 14, 9, 9, 9, 9, 9, 13, 9, 9, 9, 9, 9, 13,
9, 9, 9, 9, 9, 13, 9, 9, 9, 9, 9, 13, 9, 9, 9, 9,
9, 13, 11, 11, 11, 11, 11, 15, 0, 0, 0, 0, 0, 0, 8, 8,
8, 8, 8, 8, 7, 7, 7, 7, 7, 7, 15, 15, 15, 15, 15, 15,
}
)