Colorspace.h

#ifndef DASH__TOOLS__COLORSPACE
#define DASH__TOOLS__COLORSPACE

namespace dash {
namespace tools {
namespace color {

typedef struct {
  double r; // percent
  double g; // percent
  double b; // percent
} rgb;

typedef struct {
  double h; // angle in degrees
  double s; // percent
  double v; // percent
} hsv;

static hsv   rgb2hsv(rgb in);
static rgb   hsv2rgb(hsv in);

hsv rgb2hsv(rgb in)
{
  hsv         out;
  double      min, max, delta;

  min = in.r < in.g ? in.r : in.g;
  min = min  < in.b ? min  : in.b;

  max = in.r > in.g ? in.r : in.g;
  max = max  > in.b ? max  : in.b;

  out.v = max;                              // v
  delta = max - min;
  if (delta < 0.00001) {
    out.s = 0;
    out.h = 0; // undefined, maybe nan?
    return out;
  }
  if ( max > 0.0 ) {
    out.s = (delta / max);                  // s
  } else {
    // if max is 0, then r = g = b = 0
    // s = 0, v is undefined
    out.s = 0.0;
    out.h = NAN;                            // its now undefined
    return out;
  }
  if (in.r >= max) {
    // between yellow & magenta
    out.h = ( in.g - in.b ) / delta;
  } else if ( in.g >= max ) {
    out.h = 2.0 + ( in.b - in.r ) / delta;  // between cyan & yellow
  } else {
    out.h = 4.0 + ( in.r - in.g ) / delta;  // between magenta & cyan
  }

  out.h *= 60.0;                            // degrees

  if ( out.h < 0.0 ) {
    out.h += 360.0;
  }

  return out;
}


rgb hsv2rgb(hsv in)
{
  double      hh, p, q, t, ff;
  long        i;
  rgb         out;

  if (in.s <= 0.0) {      // < is bogus, just shuts up warnings
    out.r = in.v;
    out.g = in.v;
    out.b = in.v;
    return out;
  }
  hh = in.h;
  if (hh >= 360.0) {
    hh = 0.0;
  }
  hh /= 60.0;
  i = (long)hh;
  ff = hh - i;
  p = in.v * (1.0 - in.s);
  q = in.v * (1.0 - (in.s * ff));
  t = in.v * (1.0 - (in.s * (1.0 - ff)));

  switch (i) {
  case 0:
    out.r = in.v;
    out.g = t;
    out.b = p;
    break;
  case 1:
    out.r = q;
    out.g = in.v;
    out.b = p;
    break;
  case 2:
    out.r = p;
    out.g = in.v;
    out.b = t;
    break;

  case 3:
    out.r = p;
    out.g = q;
    out.b = in.v;
    break;
  case 4:
    out.r = t;
    out.g = p;
    out.b = in.v;
    break;
  case 5:
  default:
    out.r = in.v;
    out.g = p;
    out.b = q;
    break;
  }
  return out;
}

} // namespace color
} // namespace tools
} // namespace dash

#endif // DASH__TOOLS__COLORSPACE