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#![deny(unsafe_code)]
#![allow(clippy::many_single_char_names)]
const ANSI256_FROM_GREY: [u8; 256] = [
16, 16, 16, 16, 16, 232, 232, 232, 232, 232, 232, 232, 232, 232, 233, 233, 233, 233, 233, 233,
233, 233, 233, 233, 234, 234, 234, 234, 234, 234, 234, 234, 234, 234, 235, 235, 235, 235, 235,
235, 235, 235, 235, 235, 236, 236, 236, 236, 236, 236, 236, 236, 236, 236, 237, 237, 237, 237,
237, 237, 237, 237, 237, 237, 238, 238, 238, 238, 238, 238, 238, 238, 238, 238, 239, 239, 239,
239, 239, 239, 239, 239, 239, 239, 240, 240, 240, 240, 240, 240, 240, 240, 59, 59, 59, 59, 59,
241, 241, 241, 241, 241, 241, 241, 242, 242, 242, 242, 242, 242, 242, 242, 242, 242, 243, 243,
243, 243, 243, 243, 243, 243, 243, 244, 244, 244, 244, 244, 244, 244, 244, 244, 102, 102, 102,
102, 102, 245, 245, 245, 245, 245, 245, 246, 246, 246, 246, 246, 246, 246, 246, 246, 246, 247,
247, 247, 247, 247, 247, 247, 247, 247, 247, 248, 248, 248, 248, 248, 248, 248, 248, 248, 145,
145, 145, 145, 145, 249, 249, 249, 249, 249, 249, 250, 250, 250, 250, 250, 250, 250, 250, 250,
250, 251, 251, 251, 251, 251, 251, 251, 251, 251, 251, 252, 252, 252, 252, 252, 252, 252, 252,
252, 188, 188, 188, 188, 188, 253, 253, 253, 253, 253, 253, 254, 254, 254, 254, 254, 254, 254,
254, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 231, 231,
231, 231, 231, 231, 231, 231, 231,
];
pub const fn rgb_to_ansi256(r: u8, g: u8, b: u8) -> u8 {
let rgb = ((r as u32) << 16) + ((g as u32) << 8) + b as u32;
if r == g && g == b {
return ANSI256_FROM_GREY[(rgb as usize) & 0xff];
}
let grey_index: u8 = ANSI256_FROM_GREY[luminance(rgb) as usize];
let grey_distance: u32 = distance(rgb, rgb_from_ansi256(grey_index));
let cube: u32 = cube_index_red(r) + cube_index_green(g) + cube_index_blue(b);
if distance(rgb, cube) < grey_distance {
(cube >> 24) as u8
} else {
grey_index
}
}
const fn luminance(rgb: u32) -> u8 {
let v: u32 =
3567664u32 * (rgb >> 16 & 0xff) + 11998547u32 * (rgb >> 8 & 0xff) + 1211005 * (rgb & 0xff);
((v + (1 << 23)) >> 24) as u8
}
const fn rgb_from_ansi256(index: u8) -> u32 {
const SYSTEM_COLOURS: [u32; 16] = [
0x000000, 0xcd0000, 0x00cd00, 0xcdcd00, 0x0000ee, 0xcd00cd, 0x00cdcd, 0xe5e5e5, 0x7f7f7f,
0xff0000, 0x00ff00, 0xffff00, 0x5c5cff, 0xff00ff, 0x00ffff, 0xffffff,
];
if index < 16 {
SYSTEM_COLOURS[index as usize]
} else if index < 232 {
let index = index - 16;
(cube_value(index / 36) << 16) | (cube_value(index / 6 % 6) << 8) | (cube_value(index % 6))
} else {
let index = (index - 232) * 10 + 8;
(index as u32) * 0x010101
}
}
const fn cube_value(idx: u8) -> u32 {
[0, 95, 135, 175, 215, 255][idx as usize]
}
const fn distance(x: u32, y: u32) -> u32 {
const fn r(c: u32) -> i32 {
((c >> 16) & 0xff) as i32
}
const fn g(c: u32) -> i32 {
((c >> 8) & 0xff) as i32
}
const fn b(c: u32) -> i32 {
(c & 0xff) as i32
}
let r_sum: i32 = r(x) + r(y);
let r = r(x) - r(y);
let g = g(x) - g(y);
let b = b(x) - b(y);
((1024 + r_sum) * r * r + 2048 * g * g + (1534 - r_sum) * b * b) as u32
}
#[rustfmt::skip]
macro_rules! cube_thresholds {
($v:ident, $a:expr, $b:expr, $c:expr, $d:expr, $e:expr, $idx:ident) => {
if $v < $a { $idx(0, 0) }
else if $v < $b { $idx(1, 95) }
else if $v < $c { $idx(2, 135) }
else if $v < $d { $idx(3, 175) }
else if $v < $e { $idx(4, 215) }
else { $idx(5, 255) }
}
}
const fn cube_index_red(v: u8) -> u32 {
const fn idx(i: u32, v: u32) -> u32 {
((i * 36 + 16) << 24) | (v << 16)
}
cube_thresholds!(v, 38, 115, 155, 196, 235, idx)
}
const fn cube_index_green(v: u8) -> u32 {
const fn idx(i: u32, v: u32) -> u32 {
((i * 6) << 24) | (v << 8)
}
cube_thresholds!(v, 36, 116, 154, 195, 235, idx)
}
const fn cube_index_blue(v: u8) -> u32 {
const fn idx(i: u32, v: u32) -> u32 {
(i << 24) | v
}
cube_thresholds!(v, 35, 115, 155, 195, 235, idx)
}
#[cfg(test)]
mod tests {
use super::rgb_to_ansi256;
const MEDIUM_SPRING_GREEN: u8 = rgb_to_ansi256(0, 255, 175);
#[test]
fn validate_const_eval() {
assert_eq!(MEDIUM_SPRING_GREEN, 49);
}
#[test]
fn validate_with_ansi_colours() {
for r in 0..=255 {
for g in 0..=255 {
for b in 0..=255 {
let got = rgb_to_ansi256(r, g, b);
let expected = ansi_colours::ansi256_from_rgb((r, g, b));
assert_eq!(expected, got, "r={}, g={}, b={}", r, g, b);
}
}
}
}
}