             vec4 currentColor = vec4(0.0f, 0.0f, 0.0f, TFColor.a);
             if (squareGradientLength > 0.05f)
             {
-              currentColor.xyz = calculateLighting(TFColor, startpos_eye, gradient);
+              currentColor.xyz = calculateLighting(TFColor, startPos_eye, gradient);
             }
             else
             {

  }
}

vec3 calculateLighting(vec4 color, vec3 startpos_eye, vec3 gradient)
{
  const vec3 lightPos = vec3(0.0f, 0.0f, 0.0f);
  vec3 lightDir = normalize(lightPos - startpos_eye);
  vec3 viewDir = -1.0f * normalize(startpos_eye);
  vec3 normalizedGradient = normalize(gradient);

  // float dotNL = abs(dot(ngradient, lightDir));

            break;

          // prepare next segment
          lastPos_eye = startPos_eye;
          startPos_eye += stepFactor * direction_eye;

          // FIXME: do we need it?
          // pos_proj = gl_ProjectionMatrix*vec4(startPos_eye,1.0f);
          // pos_proj.z /= pos_proj.w;
          // pos_proj.z += 1.0f;
          // pos_proj.z /=2.0f;
        }  // sampling steps

        finalColor = finalColor + fragmentColor * (1.0f - finalColor.a);
      }  // if (activeObjectCount > 0) ...
    }
    else
    {
