void surfaceFunction(VertexIn In, out RangeOut Out)
{ 
    Out.Attributes = float4(In.Attributes.r, 0, 0, 1);
}

SurfaceOut surfaceFunction(VertexIn In)
{
  SurfaceOut Out = (SurfaceOut)0;

  float v = smoothstep(range.x, range.y, In.Attributes.r);

  float m = 0.1;
  Out.Color = lerp(
    lerp(float4(m, m, m, 1), float4(m, m, 0.8, 1), smoothstep(0, 0.33, v)),
    lerp(float4(m, 0.8, m, 1), float4(0.8, m, m, 1), smoothstep(0.66, 1, v)),
    smoothstep(0.33, 0.66, v));

  float3 normalX = ddx_fine(In.ViewSpacePosition.xyz);
  float3 normalY = ddy_fine(In.ViewSpacePosition.xyz);

  float3 normal = normalize(cross(normalY, normalX));

  Out.Normal = normal;
  Out.LightModel = 1;

  return Out;
}