anchor.diff:  
   Here is what indirect specular alone, looks like, with a roughness of 0.1.
   
  -image::IndirectSpeculra.png[IndirectSpeculra,width="320",height="250",align="center"]
  +image::jme3/advanced/IndirectSpeculra.png[IndirectSpeculra,width="320",height="250",align="center"]
   
   *So in the end :*
   
  
positive.code: *Importance Sampling :* A math technique to approximate the result of an integral.
  
  *Split Sum Approximation :* A way,used in Unreal Engine 4, to transform the specular radiance integral into 2 sums that can be easily baked into prefiltered textures.
  
negative.code: 
  But, as we are preprocessing the map, we don’t have any information about the shaded surface normal and view direction. So we are going to assume they are all the same, and equal to the envVector we’ll use to fetch pixels from the map. Also we assume that the shading point is exactly at the center of the cube map.
  
  image::jme3/advanced/prefilteredEnvMapSampling.png[prefilteredEnvMapSampling,width="320",height="250",align="center"]
  
  This is an approximation again, and it has a cost in quality, but we’re all for approximation as long as it’s perform faster while still looking good, right?
  
  Here is what the result looks like
  
  image::jme3/advanced/PrefilteredEnvMap.png[PrefilteredEnvMap,width="320",height="250",align="center"]
  The prefiltered environment map, with the different mip levels. notice how the blur increases through them.
  
  So now we can evaluate the first sum of the split sum approximation with a single texture fetch. We are going to compute the Lod level (the mip level where to fetch the texel) according to the roughness.
  