"folkert" <fol### [at] vanheusdencom> wrote:
> Hello,
>
> I'm trying to add normals to triangles.
>
> Let's say I've got this mesh2 object:
>
>
> mesh2 {
>   vertex_vectors {
>     4
> , <-4.22827, 3.07201, 49.7261>, <-3.49716, 3.88399, 49.7261>, <-10.3386,
> 11.4822, 47.5528>, <-12.5, 9.08178, 47.5528>  }
>   face_indices {
>     2
> , <2, 0, 1>, <0, 2, 3>
>   }
>
>   texture { pigment { color rgbf <0.976471, 0.843137, 0.172549, 0> } }
>   finish { MATERIAL } interior { MATERIAL_INT }
> }
>
> This renders fine.
> So next step, adding normals.
>
> Am I right that I need to do the following:
> - for each triangle, e.g.:
>   p1: <-10.3386, 11.4822, 47.5528>, p2: <-4.22827, 3.07201, 49.7261>, p3:
> <-3.49716, 3.88399, 49.7261>
>   and
>   q1: <-4.22827, 3.07201, 49.7261>, q2: <-10.3386, 11.4822, 47.5528>, q3:
> <-12.5, 9.08178, 47.5528>
>   calculate the normals:
>     normal 1 = (p2 - p1) * (p3 - p1)
>     normal 2 = (p3 - p2) * (p2 - p1)
>     normal 3 = (p2 - p3) * (p2 - p1)
>     normal 4 = (q2 - q1) * (q3 - q1)
>     normal 5 = (q3 - q2) * (q2 - q1)
>     normal 6 = (q2 - q3) * (q2 - q1)
> - then put those normals in a:
>   normals_vectors {
>      6, (normal 1), (normal 2), etc.
>   }
>
> But then I'm lost. What should I put in normal_indices { } ?

Normal indices list is optional if there is the same number of normals and
vertices. If so, the indices from the face_indices{} list are used instead.
Otherwise, each entry of the normals list points to what vertices a normal
should be applied. thus providing "shared normals" groups usefull in case of
partly smooth partly flat models... cf docs:
https://www.povray.org/documentation/view/3.60/68/

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