Le 10/06/2019 à 19:35, Cousin Ricky a écrit :
> Such a solution would have obvious application toward uv-textured sphere
> sweeps. 

sphere_sweep have been uv-mapped (in hgpovray).

Basic approach: an initial vector and the first 2 points define the
origin for one uv axis, as two normals. It's arbitrary anyway, but being
predictable and adjustable is better when using uv-mapping.

(the two normals and the oriented segment make a local 3D reference
system that is going to slide along the sphere sweep)

On each successive point, compute the plane in which the rotation is
occurring (3 poins, one plane) and propagate the normals on next segment
using the "natural" rotation in the plane. Repeat until there is no more
point.

Alas, currently in hgpovray38, sphere_sweep is not marked as UVMeshable,
so you cannot read back the data from uv values using uv_min, uv_max,
uv_vertex and uv_normal (also extension of hgpovray38).

Nevertheless, you can use trace() as usual to retrieve the uv value if
you known how to have an intersection (hint: middle of a segment and
trying two perpendicular vectors, for linear sphere sweep; more
difficult for the other types)

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