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