1/*
2 * Copyright 2024, Haiku, Inc. All rights reserved.
3 * Distributed under the terms of the MIT License.
4 */
5
6
7#include <HSL.h>
8
9
10hsl_color
11hsl_color::from_rgb(const rgb_color& rgb)
12{
13	hsl_color result;
14
15	float r = rgb.red / 255.0f;
16	float g = rgb.green / 255.0f;
17	float b = rgb.blue / 255.0f;
18
19	float max = max_c(max_c(r, g), b);
20	float min = min_c(min_c(r, g), b);
21
22	result.hue = result.saturation = result.lightness = (max + min) / 2;
23
24	if (max == min) {
25		// grayscale
26		result.hue = result.saturation = 0;
27	} else {
28		float diff = max - min;
29		result.saturation
30			= (result.lightness > 0.5) ? (diff / (2 - max - min)) : (diff / (max + min));
31
32		if (max == r)
33			result.hue = (g - b) / diff + (g < b ? 6 : 0);
34		else if (max == g)
35			result.hue = (b - r) / diff + 2;
36		else if (max == b)
37			result.hue = (r - g) / diff + 4;
38
39		result.hue /= 6;
40	}
41
42	return result;
43}
44
45
46rgb_color
47hsl_color::to_rgb() const
48{
49	rgb_color result;
50	result.alpha = 255;
51
52	if (saturation == 0) {
53		// grayscale
54		result.red = result.green = result.blue = uint8(lightness * 255);
55	} else {
56		float q = lightness < 0.5 ? (lightness * (1 + saturation))
57			: (lightness + saturation - lightness * saturation);
58		float p = 2 * lightness - q;
59		result.red = uint8(hue_to_rgb(p, q, hue + 1./3) * 255);
60		result.green = uint8(hue_to_rgb(p, q, hue) * 255);
61		result.blue = uint8(hue_to_rgb(p, q, hue - 1./3) * 255);
62	}
63
64	return result;
65}
66
67
68// reference: https://en.wikipedia.org/wiki/HSL_and_HSV#Color_conversion_formulae
69// (from_rgb() and to_rgb() are derived from the same)
70float
71hsl_color::hue_to_rgb(float p, float q, float t)
72{
73	if (t < 0)
74		t += 1;
75	if (t > 1)
76		t -= 1;
77	if (t < 1./6)
78		return p + (q - p) * 6 * t;
79	if (t < 1./2)
80		return q;
81	if (t < 2./3)
82		return p + (q - p) * (2./3 - t) * 6;
83
84	return p;
85}
86