vec4 VolRender()

in packages/miew/src/gfx/shaders/Volume.frag [154:219]
61 lines of code
10 McCabe index (conditional complexity)

vec4 VolRender(vec3 start, vec3 back, float molDist, vec3 dir) {
  vec4 acc = NO_COLOR, iso;
  vec3 iterator = start, sumColor = vec3(0., 0., 0.);
  float stepSize, alpha, sumAlpha = 0.0, vol, curStepSize, molD;
  vec3 step, col, colOld, right;
  float tr0 = _isoLevel0.x;
  float dif, r, kd, finish;
  int count = 0, stopMol = 0;

  for (int k = 0; k < 3; k++) {
    stepSize = (float(k) + 2.) / float(STEPS_COUNT);
    kd = 140. * tr0 * stepSize;
    r = 1. - kd;
    step = stepSize * dir;
    iso = GetIso1(iterator, back, molDist, dir, tr0, k);
    if (iso.a < 0.1 || length(iso.xyz - start) > molDist)
      break;
    iterator = iso.xyz;
    dif = 1.;// CalcColor(iterator, dir);
    colOld = GetColSimple(tr0);
    curStepSize = stepSize;
    for (int i = 0; i < STEPS_COUNT; i++) {
      iterator = iterator + step;
      molD = length(iterator - start);
      vol = sample3DTextureInclined(iterator).r;
      finish = distance(iterator, back) - stepSize;
      if (finish < 0.0 || vol < tr0 || (sumAlpha > 0.97) || molD > molDist)
        break;
      alpha = (1. - r);
      col = GetColSimple(vol);
      vol = sample3DTextureInclined(iterator - 0.5 * step).r;
      vec3 colMid = GetColSimple(vol);
      sumColor += (1. - sumAlpha) * (colOld + 4.* colMid + col) * alpha / 6.;
      sumAlpha += (1. - sumAlpha) * alpha;// *(1. - 1.0*dif*dif);
      colOld = col;
    } // for i

    if (finish < 0.0 || sumAlpha > 0.97)
      break;

    if (molD > molDist) {
      curStepSize = stepSize - (molD - molDist);
      right = iterator - (molD - molDist) * dir;
      vol = sample3DTextureInclined(right).r;
    } else {
      vec3 left = iterator - step;
      right = CorrectIso(left, iterator, tr0);
      curStepSize = distance(left, right);
      vol = tr0;
    }

    alpha = (1. - r) * curStepSize / stepSize;
    dif = 1.;// CalcColor(right, dir);
    col = GetColSimple(vol);
    vol = sample3DTextureInclined(iterator - 0.5 * curStepSize / stepSize * step).r;
    vec3 colMid = GetColSimple(vol);
    sumColor += (1. - sumAlpha) * (colOld + 4. * colMid + col) * alpha / 6.;
    sumAlpha += (1. - sumAlpha) * alpha;// *(1. - 1.0*dif*dif);

    if (molD > molDist)
      break;
  } // for k
  acc.rgb = 1. * sumColor / sumAlpha;
  acc.a = sumAlpha;
  return acc;
}