deltachat/
color.rs

1//! Color generation.
2//!
3//! This is similar to Consistent Color Generation defined in XEP-0392,
4//! but uses OKLCh colorspace instead of HSLuv
5//! to ensure that colors have the same lightness.
6use colorutils_rs::{Oklch, Rgb, TransferFunction};
7use sha1::{Digest, Sha1};
8
9/// Converts an identifier to Hue angle.
10#[expect(clippy::arithmetic_side_effects)]
11fn str_to_angle(s: &str) -> f32 {
12    let bytes = s.as_bytes();
13    let result = Sha1::digest(bytes);
14    let checksum: u16 = result.first().map_or(0, |&x| u16::from(x))
15        + 256 * result.get(1).map_or(0, |&x| u16::from(x));
16    f32::from(checksum) / 65536.0 * 360.0
17}
18
19/// Converts RGB tuple to a 24-bit number.
20///
21/// Returns a 24-bit number with 8 least significant bits corresponding to the blue color and 8
22/// most significant bits corresponding to the red color.
23#[expect(clippy::arithmetic_side_effects)]
24fn rgb_to_u32(rgb: Rgb<u8>) -> u32 {
25    65536 * u32::from(rgb.r) + 256 * u32::from(rgb.g) + u32::from(rgb.b)
26}
27
28/// Converts an identifier to RGB color.
29///
30/// Lightness is set to half (0.5) to make colors suitable both for light and dark theme.
31pub fn str_to_color(s: &str) -> u32 {
32    let lightness = 0.5;
33    let chroma = 0.23;
34    let angle = str_to_angle(s);
35    let oklch = Oklch::new(lightness, chroma, angle);
36    let rgb = oklch.to_rgb(TransferFunction::Srgb);
37
38    rgb_to_u32(rgb)
39}
40
41/// Returns color as a "#RRGGBB" `String` where R, G, B are hex digits.
42pub fn color_int_to_hex_string(color: u32) -> String {
43    format!("{color:#08x}").replace("0x", "#")
44}
45
46#[cfg(test)]
47mod tests {
48    use super::*;
49
50    #[test]
51    #[allow(clippy::excessive_precision)]
52    fn test_str_to_angle() {
53        // Test against test vectors from
54        // <https://xmpp.org/extensions/xep-0392.html#testvectors-fullrange-no-cvd>
55        assert!((str_to_angle("Romeo") - 327.255249).abs() < 1e-6);
56        assert!((str_to_angle("juliet@capulet.lit") - 209.410400).abs() < 1e-6);
57        assert!((str_to_angle("😺") - 331.199341).abs() < 1e-6);
58        assert!((str_to_angle("council") - 359.994507).abs() < 1e-6);
59        assert!((str_to_angle("Board") - 171.430664).abs() < 1e-6);
60    }
61
62    #[test]
63    fn test_rgb_to_u32() {
64        assert_eq!(rgb_to_u32(Rgb::new(0, 0, 0)), 0);
65        assert_eq!(rgb_to_u32(Rgb::new(0xff, 0xff, 0xff)), 0xffffff);
66        assert_eq!(rgb_to_u32(Rgb::new(0, 0, 0xff)), 0x0000ff);
67        assert_eq!(rgb_to_u32(Rgb::new(0, 0xff, 0)), 0x00ff00);
68        assert_eq!(rgb_to_u32(Rgb::new(0xff, 0, 0)), 0xff0000);
69        assert_eq!(rgb_to_u32(Rgb::new(0xff, 0x80, 0)), 0xff8000);
70    }
71}
deltachat/color.rs

deltachat/
color.rs
