makeover 3.5.1

Shared theme loading for the make-family apps: TOML theme files parsed into intent-based color tokens, with perceptual derivations and WCAG contrast.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265

//! Color math — perceptual (OKLab) derivations + WCAG contrast.
//!
//! Interactive states (hover/active/selection/surfaces) are derived in OKLab so
//! equal steps look equal across every theme's hues (Ottosson 2020; the modern
//! CIELAB). Text-on-color is picked by the WCAG 2.x contrast ratio, not a naive
//! luminance threshold, so the choice actually meets AA where achievable.
//! This is the single source of truth shared by every product.

/// An sRGB color. Hex round-trips losslessly.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct Rgb {
    pub r: u8,
    pub g: u8,
    pub b: u8,
}

impl Rgb {
    /// Parse `#rgb` or `#rrggbb` (case-insensitive). Returns `None` otherwise.
    pub fn from_hex(s: &str) -> Option<Rgb> {
        let h = s.strip_prefix('#')?;
        let (r, g, b) = match h.len() {
            6 => (
                u8::from_str_radix(&h[0..2], 16).ok()?,
                u8::from_str_radix(&h[2..4], 16).ok()?,
                u8::from_str_radix(&h[4..6], 16).ok()?,
            ),
            3 => {
                let d = |c: &str| u8::from_str_radix(c, 16).ok().map(|v| v * 17);
                (d(&h[0..1])?, d(&h[1..2])?, d(&h[2..3])?)
            }
            _ => return None,
        };
        Some(Rgb { r, g, b })
    }

    /// Lowercase `#rrggbb`.
    pub fn to_hex(self) -> String {
        format!("#{:02x}{:02x}{:02x}", self.r, self.g, self.b)
    }

    pub fn tuple(self) -> (u8, u8, u8) {
        (self.r, self.g, self.b)
    }
}

/// A color in OKLab (perceptually uniform): `l` lightness in \[0,1\], `a`/`b` opponent axes.
#[derive(Clone, Copy, Debug)]
pub struct Oklab {
    pub l: f32,
    pub a: f32,
    pub b: f32,
}

fn srgb_to_linear(c: u8) -> f32 {
    let c = c as f32 / 255.0;
    if c <= 0.04045 {
        c / 12.92
    } else {
        ((c + 0.055) / 1.055).powf(2.4)
    }
}

fn linear_to_srgb(c: f32) -> u8 {
    let c = c.clamp(0.0, 1.0);
    let v = if c <= 0.0031308 {
        c * 12.92
    } else {
        1.055 * c.powf(1.0 / 2.4) - 0.055
    };
    (v * 255.0).round().clamp(0.0, 255.0) as u8
}

impl Rgb {
    /// Convert to OKLab (Ottosson's sRGB matrices).
    ///
    /// The matrix coefficients are quoted at their published precision so they
    /// can be diffed against the reference. `f32` rounds them at compile time;
    /// truncating the literals would only make them harder to check.
    #[allow(clippy::excessive_precision)]
    pub fn to_oklab(self) -> Oklab {
        let (r, g, b) = (
            srgb_to_linear(self.r),
            srgb_to_linear(self.g),
            srgb_to_linear(self.b),
        );
        let l = 0.4122214708 * r + 0.5363325363 * g + 0.0514459929 * b;
        let m = 0.2119034982 * r + 0.6806995451 * g + 0.1073969566 * b;
        let s = 0.0883024619 * r + 0.2817188376 * g + 0.6299787005 * b;
        let (l_, m_, s_) = (l.cbrt(), m.cbrt(), s.cbrt());
        Oklab {
            l: 0.2104542553 * l_ + 0.7936177850 * m_ - 0.0040720468 * s_,
            a: 1.9779984951 * l_ - 2.4285922050 * m_ + 0.4505937099 * s_,
            b: 0.0259040371 * l_ + 0.7827717662 * m_ - 0.8086757660 * s_,
        }
    }

    /// Convert from OKLab back to the nearest in-gamut sRGB.
    ///
    /// Published precision, as in [`Rgb::to_oklab`].
    #[allow(clippy::excessive_precision)]
    pub fn from_oklab(c: Oklab) -> Rgb {
        let l_ = c.l + 0.3963377774 * c.a + 0.2158037573 * c.b;
        let m_ = c.l - 0.1055613458 * c.a - 0.0638541728 * c.b;
        let s_ = c.l - 0.0894841775 * c.a - 1.2914855480 * c.b;
        let (l, m, s) = (l_ * l_ * l_, m_ * m_ * m_, s_ * s_ * s_);
        Rgb {
            r: linear_to_srgb(4.0767416621 * l - 3.3077115913 * m + 0.2309699292 * s),
            g: linear_to_srgb(-1.2684380046 * l + 2.6097574011 * m - 0.3413193965 * s),
            b: linear_to_srgb(-0.0041960863 * l - 0.7034186147 * m + 1.7076147010 * s),
        }
    }
}

/// WCAG 2.x relative luminance of an sRGB color.
pub(crate) fn rel_luminance(c: Rgb) -> f32 {
    0.2126 * srgb_to_linear(c.r) + 0.7152 * srgb_to_linear(c.g) + 0.0722 * srgb_to_linear(c.b)
}

/// WCAG 2.x contrast ratio between two colors, in [1, 21].
pub fn wcag_contrast(a: Rgb, b: Rgb) -> f32 {
    let (la, lb) = (rel_luminance(a), rel_luminance(b));
    let (hi, lo) = if la >= lb { (la, lb) } else { (lb, la) };
    (hi + 0.05) / (lo + 0.05)
}

/// Pick black or white for legible text on `bg`, by the higher WCAG contrast
/// ratio (so the choice meets AA wherever the background allows it).
pub fn readable_on(bg: Rgb) -> Rgb {
    let white = Rgb {
        r: 255,
        g: 255,
        b: 255,
    };
    let black = Rgb { r: 0, g: 0, b: 0 };
    if wcag_contrast(white, bg) >= wcag_contrast(black, bg) {
        white
    } else {
        black
    }
}

/// Shift OKLab lightness by `delta` (perceptually uniform). Positive lightens.
pub fn lighten(c: Rgb, delta: f32) -> Rgb {
    let mut lab = c.to_oklab();
    lab.l = (lab.l + delta).clamp(0.0, 1.0);
    Rgb::from_oklab(lab)
}

/// Shift OKLab lightness down by `delta` (perceptually uniform).
pub fn darken(c: Rgb, delta: f32) -> Rgb {
    lighten(c, -delta)
}

/// Interpolate between `a` and `b` by `t` in \[0,1\] in OKLab (perceptual blend).
pub fn mix(a: Rgb, b: Rgb, t: f32) -> Rgb {
    let (x, y) = (a.to_oklab(), b.to_oklab());
    Rgb::from_oklab(Oklab {
        l: x.l + (y.l - x.l) * t,
        a: x.a + (y.a - x.a) * t,
        b: x.b + (y.b - x.b) * t,
    })
}

#[cfg(test)]
mod tests {
    use super::*;

    // ---- color math (formulas must match the apps they came from) ----

    #[test]
    fn rgb_hex_roundtrip() {
        assert_eq!(
            Rgb::from_hex("#6196FF").unwrap(),
            Rgb {
                r: 0x61,
                g: 0x96,
                b: 0xff
            }
        );
        assert_eq!(
            Rgb::from_hex("#abc").unwrap(),
            Rgb {
                r: 0xaa,
                g: 0xbb,
                b: 0xcc
            }
        );
        assert_eq!(
            Rgb {
                r: 0x61,
                g: 0x96,
                b: 0xff
            }
            .to_hex(),
            "#6196ff"
        );
        assert!(Rgb::from_hex("not-a-color").is_none());
    }

    #[test]
    fn oklab_roundtrips_within_tolerance() {
        for hex in ["#6196ff", "#2e3440", "#ffffff", "#000000", "#c0392b"] {
            let c = Rgb::from_hex(hex).unwrap();
            let back = Rgb::from_oklab(c.to_oklab());
            // Gamut round-trip is near-exact (±1 per channel from rounding).
            assert!((c.r as i16 - back.r as i16).abs() <= 1, "{hex} r");
            assert!((c.g as i16 - back.g as i16).abs() <= 1, "{hex} g");
            assert!((c.b as i16 - back.b as i16).abs() <= 1, "{hex} b");
        }
    }

    #[test]
    fn wcag_contrast_known_pairs() {
        let white = Rgb {
            r: 255,
            g: 255,
            b: 255,
        };
        let black = Rgb { r: 0, g: 0, b: 0 };
        assert!((wcag_contrast(white, black) - 21.0).abs() < 0.01);
        assert!((wcag_contrast(white, white) - 1.0).abs() < 0.01);
    }

    #[test]
    fn readable_on_picks_by_wcag() {
        assert_eq!(
            readable_on(Rgb {
                r: 255,
                g: 255,
                b: 255
            }),
            Rgb { r: 0, g: 0, b: 0 }
        );
        assert_eq!(
            readable_on(Rgb { r: 0, g: 0, b: 0 }),
            Rgb {
                r: 255,
                g: 255,
                b: 255
            }
        );
        // A light blue action -> black text reads better.
        let action = Rgb::from_hex("#6196ff").unwrap();
        assert_eq!(readable_on(action), Rgb { r: 0, g: 0, b: 0 });
    }

    #[test]
    fn lighten_darken_move_oklab_lightness() {
        let c = Rgb::from_hex("#6196ff").unwrap();
        let l0 = c.to_oklab().l;
        assert!(lighten(c, 0.05).to_oklab().l > l0);
        assert!(darken(c, 0.05).to_oklab().l < l0);
    }

    #[test]
    fn mix_endpoints_and_midpoint() {
        let a = Rgb::from_hex("#000000").unwrap();
        let b = Rgb::from_hex("#6196ff").unwrap();
        assert_eq!(mix(a, b, 0.0), a);
        assert_eq!(mix(a, b, 1.0), b);
        // Midpoint sits between the endpoints in OKLab lightness.
        let mid = mix(a, b, 0.5).to_oklab().l;
        assert!(mid > a.to_oklab().l && mid < b.to_oklab().l);
    }
}