flying-balls/color.cc

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#include "color.h"
// taken from
// https://stackoverflow.com/questions/3018313/algorithm-to-convert-rgb-to-hsv-and-hsv-to-rgb-in-range-0-255-for-both
hsv_t rgb2hsv(color_t in) {
hsv_t out;
double min, max, delta;
min = in.red < in.green ? in.red : in.green;
min = min < in.blue ? min : in.blue;
max = in.red > in.green ? in.red : in.green;
max = max > in.blue ? max : in.blue;
out.val = max; // v
delta = max - min;
if (delta < 0.00001) {
out.sat = 0;
out.hue = 0; // undefined, maybe nan?
return out;
}
if (max > 0.0) { // NOTE: if Max is == 0, this divide would cause a crash
out.sat = (delta / max); // s
} else {
// if max is 0, then r = g = b = 0
// s = 0, h is undefined
out.sat = 0.0;
out.hue = NAN; // its now undefined
return out;
}
if (in.red >= max) // > is bogus, just keeps compilor happy
out.hue = (in.green - in.blue) / delta; // between yellow & magenta
else if (in.green >= max)
out.hue = 2.0 + (in.blue - in.red) / delta; // between cyan & yellow
else
out.hue = 4.0 + (in.red - in.green) / delta; // between magenta & cyan
out.hue *= 60.0; // degrees
if (out.hue < 0.0)
out.hue += 360.0;
return out;
}
color_t hsv2rgb(hsv_t in) {
double hh, p, q, t, ff;
long i;
color_t out;
if (in.sat <= 0.0) { // < is bogus, just shuts up warnings
out.red = in.val;
out.green = in.val;
out.blue = in.val;
return out;
}
hh = in.hue;
if (hh >= 360.0)
hh = 0.0;
hh /= 60.0;
i = (long) hh;
ff = hh - i;
p = in.val * (1.0 - in.sat);
q = in.val * (1.0 - (in.sat * ff));
t = in.val * (1.0 - (in.sat * (1.0 - ff)));
switch (i) {
case 0:
out.red = in.val;
out.green = t;
out.blue = p;
break;
case 1:
out.red = q;
out.green = in.val;
out.blue = p;
break;
case 2:
out.red = p;
out.green = in.val;
out.blue = t;
break;
case 3:
out.red = p;
out.green = q;
out.blue = in.val;
break;
case 4:
out.red = t;
out.green = p;
out.blue = in.val;
break;
case 5:
default:
out.red = in.val;
out.green = p;
out.blue = q;
break;
}
return out;
}