True-colour ↔ ANSI terminal palette converter

ansi_colours is a library which converts between 24-bit sRGB colours and 8-bit colour palette used by ANSI terminals such as xterm on rxvt-unicode in 256-colour mode.

The most common use case is when using 24-bit colours in a terminal emulator which only support 8-bit colour palette. This package allows true-colours to be approximated by values supported by the terminal.

When mapping true-colour into available 256-colour palette (of which only 240 are actually usable), this package tries to balance accuracy and performance. It doesn’t implement the fastest algorithm nor is it the most accurate, instead it uses a formula which should be fast enough and accurate enough for most use-cases.

Usage

This library has C, C++ and Rust bindings and can be easily used from any of those languages.

For best performance the package contains two separate (but equivalent) implementations of the conversion algorithms: one written in C and another written in Rust. Since version 1.0.4 the Rust crate has sped up by over 25% when doing True Colour → ANSI index conversion and % when doing conversion in the other direction.

Rust

Using this package with Cargo projects is as simple as adding a single dependency:

toml [dependencies] ansi_colours = "1.1"

and then using one of the two functions that the library provides:

```rust extern crate ansi_colours;

use ansi_colours::*;

fn main() { // Colour at given index: println!("{:-3}: {:?}", 50, rgbfromansi256(50));

// Approximate true-colour by colour in the palette:
let rgb = (100, 200, 150);
let index = ansi256_from_rgb(rgb);
println!("{:?} ~ {:-3} {:?}", rgb, index, rgb_from_ansi256(index));

} ```

To facilitate better interoperability, since version 1.1, this crate supports the rgb::RGB type defined by rgb crate. The support is controlled by an rgb feature. With it enabled (which is the default), ansi256_from_rgb function will accept RGB<u8> and RGB<u16> values as arguments though rgb_from_ansi256 will still return

C and C++

The easiest way to use this library in C or C++ is to copy the ansi_colour.h and ansi256.c files to your project, set up compilation step for the ansi256.c file, add the header file to the include path and once all that is done use the two provided functions:

```c

include

include "ansi_colours.h"

int main() { // Colour at given index: printf("%-3u #%06x\n", 50, rgbfromansi256(50));

// Approximate true-colour by colour in the palette:
uint32_t rgb = 0x64C896;
uint8_t index = ansi256_from_rgb(rgb);
printf("#%06x ~ %-3u %06x\n", rgb, index, rgb_from_ansi256(index));

return 0;

} ```

Unfortunately neither C nor C++ ecosystem has a centralised package distribution service so there currently is no more convenient solution..