Reference:Facets Pattern
normal { facets [coords SCALE_VALUE | size FACTOR] [NORMAL_ITEMS...] }
The facets
pattern is designed to be used as a normal,
it is not suitable for use as a pigment: it will cause an error.
There are two forms of the facets pattern. One is most suited for use with rounded surfaces,
and one is most suited for use with flat surfaces.
If coords
is specified, the facets pattern creates facets with a size on the same order
as the specified SCALE_VALUE. This version of facets is most suited for use with flat surfaces, but will
also work with curved surfaces. The boundaries of the facets coincide with the boundaries of the cells in
the standard crackle pattern. The coords version of this pattern may be quite similar to a crackle normal
pattern with solid specified.
If size
is specified, the facets texture uses a different function that creates facets
only on curved surfaces. The FACTOR determines how many facets are created, with smaller values
creating more facets, but it is not directly related to any real-world measurement. The same factor
will create the same pattern of facets on a sphere of any size.
This pattern creates facets by snapping normal vectors to the closest vectors in a perturbed grid
of normal vectors. Because of this, if a surface has normal vectors that do not vary along one or more
axes, there will be no facet boundaries along those axes.