* @param attrNames reference that will be filled with the attribute names
* the number of attrNames returned depends on the degree of the polynomials / level of the SH :
* - 1 attrName for geometric position (VEC3) : name = "position" ;
* - 3 attrNames for local frame (3xVEC3) : names are "Frame_T" (Tangent), "Frame_B" (Binormal) and "Frame_N" (Normal) ;
* - 3 attrNames for local frame (3xVEC3) : names are "frameT" (Tangent), "frameB" (Binormal) and "frameN" (Normal) ;
* - N attrNames for the function coefficients (NxVEC3) : N RGB coefficients being successively the constants, the linears (v then u), the quadratics, etc. : : a0 + a1*v + a2*u + a3*u*v + a4*v^2 + a5*u^2.
* Their names are : "SLFcoefs_<i>" (where <i> is a number from 0 to N-1).
* Their names are : "SLFcoefs<i>" (where <i> is a number from 0 to N-1).
* - 3 attrNames for local frame (3xVEC3) : Tangent, Bitangent and Normal vector
* - 6 attrNames for the function coefficients (6xVEC3) : 6 RGB coefficients being successively the quadratic members, the linears and the constants (u then v) : a*u^2 + b*v^2 + c*uv + d*u + e*v +f.