FColor HSB::hsbFromRgb(const FColor& rgb) {
const auto brightness = max(
max(RGB::red(rgb), RGB::green(rgb)), RGB::blue(rgb));
auto hue = 0.0f, saturation = 0.0f;
if (not near(brightness, 0.0)) {
const auto darkest = min(
min(RGB::red(rgb), RGB::green(rgb)), RGB::blue(rgb));
const auto range = brightness - darkest;
saturation = range / brightness;
if (not near(saturation, 0.0)) {
const float r = (brightness - RGB::red(rgb)) / range;
const float g = (brightness - RGB::green(rgb)) / range;
const float b = (brightness - RGB::blue(rgb)) / range;
if (near(RGB::red(rgb), brightness))
hue = b - g;
else if (near(RGB::green(rgb), brightness))
hue = 2.0f + r - b;
else
hue = 4.0f + g - r;
hue /= 6.0f;
if (hue < 0)
hue += 1.0f;
}
}
return FColor(hue, saturation, brightness, rgb.alpha());
}
// from http://www.cs.rit.edu/~ncs/color/t_convert.html
FColor HSB::hsbToRgb(const FColor& hsb) {
auto h = hue(hsb), s = saturation(hsb), b = brightness(hsb);
float red, green, blue;
if (s == 0) {
// achromatic (grey)
red = green = blue = b;
} else {
h *= 6; // sector 0 to 5
int i = floor(h);
auto f = h - i; // factorial part of h
auto p = b * (1 - s);
auto q = b * (1 - s * f);
auto t = b * (1 - s * (1 - f));
switch(i) {
case 0:
red = b;
green = t;
blue = p;
break;
case 1:
red = q;
green = b;
blue = p;
break;
case 2:
red = p;
green = b;
blue = t;
break;
case 3:
red = p;
green = q;
blue = b;
break;
case 4:
red = t;
green = p;
blue = b;
break;
case 5:
default:
red = b;
green = p;
blue = q;
break;
}
}
return FColor(red, green, blue, hsb.alpha());
}
