              true, // Local illumination.
              true, // Opacity correction.
              false, // Jittering.
-             true, // Clip sphere.
+             false, // Clip sphere.
              false, // Clip plane.
              false // Show what's inside the clip sphere.
             ><<<gridSize, blockSize>>>(d_output, width, height,

  sample1.z = volume<bpc>(pos - make_float3(0.0f, 0.0f, DELTA));
  sample2.z = volume<bpc>(pos + make_float3(0.0f, 0.0f, DELTA));

  N = normalize(sample2 - sample1);

  if (normal != NULL)
  {

}

template<int bpc>
__device__ float3 gradient(const float3& pos)
{
  const float DELTA = 0.01f;

  float3 sample1;
  float3 sample2;

  sample1.x = volume<bpc>(pos - make_float3(DELTA, 0.0f, 0.0f));
  sample2.x = volume<bpc>(pos + make_float3(DELTA, 0.0f, 0.0f));
  sample1.y = volume<bpc>(pos - make_float3(0.0f, DELTA, 0.0f));
