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LibGfx: Implement Color::from_hsl/hsla()

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This is required by CSS, and implemented based on the CSS standard's
algorithm.
This commit is contained in:
Sam Atkins 2021-07-19 16:38:47 +01:00 • committed by Andreas Kling
parent 4853c89c42
commit fabbd06de4
1 changed files with 54 additions and 0 deletions
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54
Userland/Libraries/LibGfx/Color.h
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@ -80,6 +80,60 @@ public:
return Color(r, g, b);
}
static constexpr Color from_hsl(double h_degrees, double s, double l) { return from_hsla(h_degrees, s, l, 1.0); }
static constexpr Color from_hsla(double h_degrees, double s, double l, double a)
{
// Algorithm from https://www.w3.org/TR/css-color-3/#hsl-color
double h = clamp(h_degrees / 360.0, 0.0, 1.0);
s = clamp(s, 0.0, 1.0);
l = clamp(l, 0.0, 1.0);
a = clamp(a, 0.0, 1.0);
// HOW TO RETURN hue.to.rgb(m1, m2, h):
auto hue_to_rgb = [](double m1, double m2, double h) -> double {
// IF h<0: PUT h+1 IN h
if (h < 0.0)
h = h + 1.0;
// IF h>1: PUT h-1 IN h
if (h > 1.0)
h = h - 1.0;
// IF h*6<1: RETURN m1+(m2-m1)*h*6
if (h * 6.0 < 1.0)
return m1 + (m2 - m1) * h * 6.0;
// IF h*2<1: RETURN m2
if (h * 2.0 < 1.0)
return m2;
// IF h*3<2: RETURN m1+(m2-m1)*(2/3-h)*6
if (h * 3.0 < 2.0)
return m1 + (m2 - m1) * (2.0 / 3.0 - h) * 6.0;
// RETURN m1
return m1;
};
// SELECT:
// l<=0.5: PUT l*(s+1) IN m2
double m2;
if (l <= 0.5)
m2 = l * (s + 1.0);
// ELSE: PUT l+s-l*s IN m2
else
m2 = l + s - l * s;
// PUT l*2-m2 IN m1
double m1 = l * 2.0 - m2;
// PUT hue.to.rgb(m1, m2, h+1/3) IN r
double r = hue_to_rgb(m1, m2, h + 1.0 / 3.0);
// PUT hue.to.rgb(m1, m2, h ) IN g
double g = hue_to_rgb(m1, m2, h);
// PUT hue.to.rgb(m1, m2, h-1/3) IN b
double b = hue_to_rgb(m1, m2, h - 1.0 / 3.0);
// RETURN (r, g, b)
u8 r_u8 = clamp(lroundf(r * 255.0), 0, 255);
u8 g_u8 = clamp(lroundf(g * 255.0), 0, 255);
u8 b_u8 = clamp(lroundf(b * 255.0), 0, 255);
u8 a_u8 = clamp(lroundf(a * 255.0), 0, 255);
return Color(r_u8, g_u8, b_u8, a_u8);
}
constexpr u8 red() const { return (m_value >> 16) & 0xff; }
constexpr u8 green() const { return (m_value >> 8) & 0xff; }
constexpr u8 blue() const { return m_value & 0xff; }