             }
 
             // clamp color
-            currentColor.xyz = clamp(currentColor.xyz, 0.0f, 1.0f);
+            currentColor.xyz = clamp(currentColor.xyz, vec3(0.0f), vec3(1.0f));
             currentColor.w = TFColor.w;
 
             // we sum up overlapping contributions

                              vec2(density, volumes[0].transferFunctionRow));

            // lighting
            if (squareGradientLength > 0.05f)
            {
              currentColor.xyz += calculateLighting(TFColor, startpos_eye, gradient);

            ao &= (~(1 << (objectID)));

            float squareGradientLength = 0.0f;
            vec4 TFColor;

            vec3 textureSamplePos =
