Re: [OT] Round 2: Webpage design and "Name That Color!"

[Adam D. Ruppe]

Here's a small program to convert HSL to RGB. Usage "hsl 60 1 0.5" for example,
where 60 is hue, 1 is saturation and 0.5 is lightness.

import std.stdio;
import std.math;
import std.conv;

struct Color {
        ubyte r;
        ubyte g;
        ubyte b;
        ubyte a;
}

Color fromHsl(real h, real s, real l) {
        h = h % 360;

        real C = (1 - abs(2 * l - 1)) * s;

        real hPrime = h / 60;

        real X = C * (1 - abs(hPrime % 2 - 1));

        real r, g, b;

        if(h is real.nan)
                r = g = b = 0;
        else if (hPrime >= 0 && hPrime < 1) {
                r = C;
                g = X;
                b = 0;
        } else if (hPrime >= 1 && hPrime < 2) {
                r = X;
                g = C;
                b = 0;
        } else if (hPrime >= 2 && hPrime < 3) {
                r = 0;
                g = C;
                b = X;
        } else if (hPrime >= 3 && hPrime < 4) {
                r = 0;
                g = X;
                b = C;
        } else if (hPrime >= 4 && hPrime < 5) {
                r = X;
                g = 0;
                b = C;
        } else if (hPrime >= 5 && hPrime < 6) {
                r = C;
                g = 0;
                b = X;
        }

        real m = l - C / 2;

        r += m;
        g += m;
        b += m;

        return Color(
                cast(ubyte)(r * 255),
                cast(ubyte)(g * 255),
                cast(ubyte)(b * 255),
                255);
}

void main(string[] args) {
        auto color = fromHsl(to!real(args[1]), to!real(args[2]), 
to!real(args[3]));

        writefln("#%02x%02x%02x", color.r, color.g, color.b);
}