A simple vertex has a float4 position x, y and z, the w I don't really know what is for. The vertex also has a float2 U and V for a texture.
When finished transforming the vertex position
Out.Position = mul(In.Position, WorldViewProj); Out.Texture = ?????
Each fragment then gets interpolated values from its primitive(3 vertices).
What do you do to get the LOD for the t.w?
I know that if the top level gives a 1:1 mapping between screen pixels and texture pixels then the top surface is used. If the second top level gives a 1:1 mapping at some distance to the screen then that level is used. And in between you interpolate two levels, that is t.w is not an integer. But how do you know at what distance the second level gives 1:1 mapping. At what depth? You would think twice as far away then the first level. Does that mean if Out.Position.z = 1 then use top level, at Out.Position.z = 2 use the second level and that Out.Position.z = 4 use the third level. At Out.Position.z = 3 then the LOD t.w is 2.5?
Shine a light please