chromashift/
hsl.rs

1use crate::{LinearRgb, Srgb, ToAlpha, round_dp};
2use core::fmt;
3
4/// An colour represented as Hue, Saturation, and Lightness expressed in the sRGB colour space.
5/// The components are:
6/// - Hue - a number between 0.0 and 360.0
7/// - Saturation - a number between 0.0 and 100.0
8/// - Brightness - 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 Hsl {
12	pub hue: f32,
13	pub saturation: f32,
14	pub lightness: f32,
15	pub alpha: f32,
16}
17
18impl Hsl {
19	pub fn new(hue: f32, saturation: f32, lightness: f32, alpha: f32) -> Self {
20		Self { hue: hue.rem_euclid(360.0), saturation, lightness, alpha: alpha.clamp(0.0, 100.0) }
21	}
22}
23
24impl ToAlpha for Hsl {
25	fn to_alpha(&self) -> f32 {
26		self.alpha
27	}
28}
29
30impl fmt::Display for Hsl {
31	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
32		let Self { hue, saturation, lightness, alpha } = self;
33		write!(
34			f,
35			"hsl({} {}% {}%",
36			round_dp(*hue as f64, 2),
37			round_dp(*saturation as f64, 2),
38			round_dp(*lightness as f64, 2)
39		)?;
40		if *alpha < 100.0 {
41			write!(f, " / {}", round_dp(*alpha as f64, 2))?;
42		}
43		write!(f, ")")
44	}
45}
46
47/// sRGB gamma-encode: linear to gamma (handles negative/OOG values via signum)
48fn gamma(u: f64) -> f64 {
49	let abs = u.abs();
50	if abs <= 0.0031308 { u * 12.92 } else { u.signum() * (1.055 * abs.powf(1.0 / 2.4) - 0.055) }
51}
52
53/// sRGB linearize: gamma to linear (handles negative/OOG values via signum)
54fn linear(c: f64) -> f64 {
55	let abs = c.abs();
56	if abs > 0.04045 { c.signum() * ((abs + 0.055) / 1.055).powf(2.4) } else { c / 12.92 }
57}
58
59/// Convert float sRGB (r,g,b in 0..1 range, but may be OOG) to HSL.
60/// This is the core algorithm that preserves out-of-gamut values.
61fn srgb_float_to_hsl(r: f64, g: f64, b: f64) -> (f64, f64, f64) {
62	let max = r.max(g).max(b);
63	let min = r.min(g).min(b);
64	let delta = max - min;
65	let lightness = (max + min) / 2.0;
66	let saturation = if delta == 0.0 { 0.0 } else { delta / (1.0 - (2.0 * lightness - 1.0).abs()) };
67	let hue = if delta == 0.0 {
68		0.0
69	} else if max == r {
70		60.0 * (((g - b) / delta) % 6.0)
71	} else if max == g {
72		60.0 * ((b - r) / delta + 2.0)
73	} else {
74		60.0 * ((r - g) / delta + 4.0)
75	};
76	let hue = if hue < 0.0 { hue + 360.0 } else { hue };
77	(hue, saturation * 100.0, lightness * 100.0)
78}
79
80/// Convert HSL to float sRGB (r,g,b in 0..1 range, but may be OOG).
81fn hsl_to_srgb_float(hue: f64, saturation: f64, lightness: f64) -> (f64, f64, f64) {
82	let h = hue / 60.0;
83	let s = saturation / 100.0;
84	let l = lightness / 100.0;
85	let c = (1.0 - (2.0 * l - 1.0).abs()) * s;
86	let x = c * (1.0 - (h % 2.0 - 1.0).abs());
87	let m = l - c / 2.0;
88	let (r_prime, g_prime, b_prime) = if h < 1.0 {
89		(c, x, 0.0)
90	} else if h < 2.0 {
91		(x, c, 0.0)
92	} else if h < 3.0 {
93		(0.0, c, x)
94	} else if h < 4.0 {
95		(0.0, x, c)
96	} else if h < 5.0 {
97		(x, 0.0, c)
98	} else {
99		(c, 0.0, x)
100	};
101	(r_prime + m, g_prime + m, b_prime + m)
102}
103
104impl From<Srgb> for Hsl {
105	fn from(value: Srgb) -> Self {
106		let r = value.red as f64 / 255.0;
107		let g = value.green as f64 / 255.0;
108		let b = value.blue as f64 / 255.0;
109		let (hue, saturation, lightness) = srgb_float_to_hsl(r, g, b);
110		Hsl::new(hue as f32, saturation as f32, lightness as f32, value.alpha)
111	}
112}
113
114impl From<Hsl> for Srgb {
115	fn from(value: Hsl) -> Self {
116		let (r, g, b) = hsl_to_srgb_float(value.hue as f64, value.saturation as f64, value.lightness as f64);
117		Srgb::new(
118			(r * 255.0).clamp(0.0, 255.0).round() as u8,
119			(g * 255.0).clamp(0.0, 255.0).round() as u8,
120			(b * 255.0).clamp(0.0, 255.0).round() as u8,
121			value.alpha,
122		)
123	}
124}
125
126impl From<LinearRgb> for Hsl {
127	fn from(value: LinearRgb) -> Self {
128		let r = gamma(value.red);
129		let g = gamma(value.green);
130		let b = gamma(value.blue);
131		let (hue, saturation, lightness) = srgb_float_to_hsl(r, g, b);
132		Hsl::new(hue as f32, saturation as f32, lightness as f32, value.alpha)
133	}
134}
135
136impl From<Hsl> for LinearRgb {
137	fn from(value: Hsl) -> Self {
138		let (r, g, b) = hsl_to_srgb_float(value.hue as f64, value.saturation as f64, value.lightness as f64);
139		LinearRgb::new(linear(r), linear(g), linear(b), value.alpha)
140	}
141}
chromashift/hsl.rs

chromashift/
hsl.rs
