chromashift/
hwb.rs

1use crate::{Hsv, LinearRgb, ToAlpha, round_dp};
2use core::fmt;
3
4/// An colour represented as Hue, Whiteness, and Blackness expressed in the sRGB colour space.
5/// The components are:
6/// - Hue - a number between 0.0 and 360.0
7/// - Whiteness - a number between 0.0 and 100.0
8/// - Blackness - a number between 0.0 and 100.0
9/// - Alpha - a number between 0.0 and 100.0
10#[derive(Debug, Clone, Copy, PartialEq)]
11pub struct Hwb {
12	pub hue: f32,
13	pub whiteness: f32,
14	pub blackness: f32,
15	pub alpha: f32,
16}
17
18impl Hwb {
19	pub fn new(hue: f32, whiteness: f32, blackness: f32, alpha: f32) -> Self {
20		Self { hue: hue.rem_euclid(360.0), whiteness, blackness, alpha: alpha.clamp(0.0, 100.0) }
21	}
22}
23
24impl ToAlpha for Hwb {
25	fn to_alpha(&self) -> f32 {
26		self.alpha
27	}
28}
29
30impl fmt::Display for Hwb {
31	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
32		let Self { hue, whiteness, blackness, alpha } = self;
33		write!(
34			f,
35			"hwb({} {} {}",
36			round_dp(*hue as f64, 2),
37			round_dp(*whiteness as f64, 3),
38			round_dp(*blackness as f64, 3)
39		)?;
40		if *alpha < 100.0 {
41			write!(f, " / {}", round_dp(*alpha as f64, 2))?;
42		}
43		write!(f, ")")
44	}
45}
46
47impl From<Hsv> for Hwb {
48	fn from(value: Hsv) -> Self {
49		let Hsv { hue, saturation, value, alpha } = value;
50		let s = saturation / 100.0;
51		let v = value / 100.0;
52		let whiteness = (1.0 - s) * v;
53		let blackness = 1.0 - v;
54		Hwb::new(hue, whiteness * 100.0, blackness * 100.0, alpha)
55	}
56}
57
58impl From<Hwb> for Hsv {
59	fn from(value: Hwb) -> Self {
60		let Hwb { hue, whiteness, blackness, alpha } = value;
61		let w = whiteness / 100.0;
62		let b = blackness / 100.0;
63		let sum = w + b;
64		let (s, v) = if sum >= 1.0 {
65			(0.0, w / sum)
66		} else {
67			let v = 1.0 - b;
68			let s = if v == 0.0 { 0.0 } else { 1.0 - w / v };
69			(s, v)
70		};
71		Hsv::new(hue, s * 100.0, v * 100.0, alpha)
72	}
73}
74
75/// sRGB gamma-encode: linear to gamma (handles negative/OOG values via signum)
76fn gamma(u: f64) -> f64 {
77	let abs = u.abs();
78	if abs <= 0.0031308 { u * 12.92 } else { u.signum() * (1.055 * abs.powf(1.0 / 2.4) - 0.055) }
79}
80
81/// sRGB linearize: gamma to linear (handles negative/OOG values via signum)
82fn linear(c: f64) -> f64 {
83	let abs = c.abs();
84	if abs > 0.04045 { c.signum() * ((abs + 0.055) / 1.055).powf(2.4) } else { c / 12.92 }
85}
86
87/// Convert float sRGB (r,g,b may be OOG) to HWB via HSV math.
88fn srgb_float_to_hwb(r: f64, g: f64, b: f64) -> (f64, f64, f64) {
89	let max = r.max(g).max(b);
90	let min = r.min(g).min(b);
91	let delta = max - min;
92	let v = max;
93	let saturation = if max == 0.0 { 0.0 } else { delta / max };
94	let hue = if delta == 0.0 {
95		0.0
96	} else if max == r {
97		60.0 * (((g - b) / delta) % 6.0)
98	} else if max == g {
99		60.0 * ((b - r) / delta + 2.0)
100	} else {
101		60.0 * ((r - g) / delta + 4.0)
102	};
103	let hue = if hue < 0.0 { hue + 360.0 } else { hue };
104	// HSV to HWB: w = (1-s)*v, b = 1-v
105	let whiteness = (1.0 - saturation) * v;
106	let blackness = 1.0 - v;
107	(hue, whiteness * 100.0, blackness * 100.0)
108}
109
110/// Convert HWB to float sRGB (r,g,b may be OOG).
111fn hwb_to_srgb_float(hue: f64, whiteness: f64, blackness: f64) -> (f64, f64, f64) {
112	let w = whiteness / 100.0;
113	let b = blackness / 100.0;
114	let sum = w + b;
115	let (s, v) = if sum >= 1.0 {
116		(0.0, w / sum)
117	} else {
118		let v = 1.0 - b;
119		let s = if v == 0.0 { 0.0 } else { 1.0 - w / v };
120		(s, v)
121	};
122	// HSV to RGB
123	let h = hue / 60.0;
124	let c = v * s;
125	let x = c * (1.0 - (h % 2.0 - 1.0).abs());
126	let m = v - c;
127	let (r_prime, g_prime, b_prime) = if h < 1.0 {
128		(c, x, 0.0)
129	} else if h < 2.0 {
130		(x, c, 0.0)
131	} else if h < 3.0 {
132		(0.0, c, x)
133	} else if h < 4.0 {
134		(0.0, x, c)
135	} else if h < 5.0 {
136		(x, 0.0, c)
137	} else {
138		(c, 0.0, x)
139	};
140	(r_prime + m, g_prime + m, b_prime + m)
141}
142
143impl From<LinearRgb> for Hwb {
144	fn from(value: LinearRgb) -> Self {
145		let r = gamma(value.red);
146		let g = gamma(value.green);
147		let b_val = gamma(value.blue);
148		let (hue, whiteness, blackness) = srgb_float_to_hwb(r, g, b_val);
149		Hwb::new(hue as f32, whiteness as f32, blackness as f32, value.alpha)
150	}
151}
152
153impl From<Hwb> for LinearRgb {
154	fn from(value: Hwb) -> Self {
155		let (r, g, b) = hwb_to_srgb_float(value.hue as f64, value.whiteness as f64, value.blackness as f64);
156		LinearRgb::new(linear(r), linear(g), linear(b), value.alpha)
157	}
158}
chromashift/hwb.rs

chromashift/
hwb.rs
