HaltonColors.cc

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//=============================================================================
//
//  CLASS HaltonColors (by Marcel Campen)
//
//=============================================================================


//== INCLUDES =================================================================


#include <ACG/Utils/HaltonColors.hh>


//== NAMESPACES ===============================================================

namespace ACG {

//== CLASS IMPLEMENTATION =========================================================


HaltonColors::HaltonColors(int skip)
{
  // skip first 250 sequence elements to lower discrepancy even further.
  current[0] = skip;
  current[1] = skip;
  current[2] = skip;

  // initialize prime bases for H,S,L. Especially the first should be small such that already
  // small numbers of generated colors are distributed over the whole color circle.
  bases[0] = 5;
  bases[1] = 13;
  bases[2] = 17;

  inverse_bases[0] = 1.0f / bases[0];
  inverse_bases[1] = 1.0f / bases[1];
  inverse_bases[2] = 1.0f / bases[2];
}

float HaltonColors::halton(int index)
{
  int base = bases[index];
  float inverse_base = inverse_bases[index];
  float H = 0;
  float half = inverse_base;
  int I = current[index];
  current[index] += 1;
  while (I > 0) {
    int digit = I % base;
    H = H + half * digit;
    I = (int)(inverse_base * (I - digit));
    half *= inverse_base;
  }
  return H;
}

float HaltonColors::random_interval(int index, float min, float max)
{
  return halton(index) * (max - min) + min;
}

ACG::Vec4f HaltonColors::HSL2RGB(double h, double sl, double l)
{
  double v;
  double r, g, b;

  r = l;
  g = l;
  b = l;

  v = (l <= 0.5) ? (l * (1.0 + sl)) : (l + sl - l * sl);

  if (v > 0) {
    double m;
    double sv;
    int sextant;
    double fract, vsf, mid1, mid2;

    m = l + l - v;
    sv = (v - m) / v;
    h *= 6.0;
    sextant = (int) h;
    fract = h - sextant;
    vsf = v * sv * fract;
    mid1 = m + vsf;
    mid2 = v - vsf;

    switch (sextant) {
      case 0:
        r = v;
        g = mid1;
        b = m;
        break;
      case 1:
        r = mid2;
        g = v;
        b = m;
        break;
      case 2:
        r = m;
        g = v;
        b = mid1;
        break;
      case 3:
        r = m;
        g = mid2;
        b = v;
        break;
      case 4:
        r = mid1;
        g = m;
        b = v;
        break;
      case 5:
        r = v;
        g = m;
        b = mid2;
        break;
    }
  }

  return Vec4f((float)r, (float)g, (float)b, 1.0f);
}

ACG::Vec4f HaltonColors::generateNextColor() {
    float h = random_interval(0, 0.0f , 0.9f ); // 0.9 instead of 1.0 to suppress natural bias towards red
    float s = random_interval(1, 0.40f, 0.80f); // saturation between 40% and 80%
    float l = random_interval(2, 0.30f, 0.60f); // lightness between 30% and 60%
    return HSL2RGB(h, s, l);
}

ACG::Vec4f HaltonColors::get_next_color()
{
    return generateNextColor();
}


//=============================================================================
} // ACG namespace end
//=============================================================================
//=============================================================================