anchor.diff:  uniform vec3 CameraPos;
   uniform vec3 Dimensions;
   
  -const int refinement_num = 4;
  -const float sampleDistance = 0.005f;
  +float sampleDistance = limit * 0.5f;
   const float IsoValue = 0.0f;
   
   out vec4 out_Color;
  
positive.code:     float density = sample(sample_pos);
  
      // check if cell is inside contour
      if (density >= IsoValue && prev_density < IsoValue ||
        density < IsoValue && prev_density >= IsoValue) {
  
        bool in_surface = true;
        for (float i = 1; i <= refinement_num; ++i) {
          if (in_surface) {
            sample_pos -= sampleStep * pow(0.5, i);
          }
          else {
            sample_pos += sampleStep * pow(0.5, i);
          }
          in_surface = sample(sample_pos) <= IsoValue;
        }
  
        float final_density = sample(sample_pos);
        vec3 view_normal = normalize((NormalMatrix * vec4(get_gradient(sample_pos), 0.0f)).xyz);
  
negative.code: const float ks = 0.5f;            // specular intensity
  const float n = 20.0f;            //specular exponent 
  
  #define SHADED
  
  vec2 phongDiffSpec(const vec3 position, const vec3 normal, const float n, const vec3 lightPos);
  vec3 get_gradient(const vec3 pos);
  