Gilles Tran wrote:
> 
> Other software call "fresnel" a shader that allow texture attribute to vary
> according to the viewing angle of a 3D surface.

In fact all shaders POV-Ray offers (although the term 'shader' is 
possibly misleading in case of a raytracer) except diffuse vary the 
color depending on the viewing angle.  It is the very definition of a 
diffuse surface that the appearance does not depend on the viewing 
angle.  The fresnel formulas specify a certain type of angle dependance 
which well describes the reflectance of an ideal specular surface and 
for this purpose it is used in POV-Ray.  To use it elsewhere, for 
example to vary the surface's own color pattern is possible (via aoi 
pattern) but would only serve artistic purposes without physical 
background so there isn't a predefined feature (like a fresnel waveform 
for use with aoi) in POV-Ray.

Christoph

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