I was digging through some bit-rotted PDL::Graphics::TriD stuff to finish/fix it, and looked at PDL::Graphics::TriD::Logo. It was intended to be used with the non-functional-right-now PDL VRML support, in particular VRML's IndexedFaceSet feature. It had 3D point coordinates, then triplets of indexes into those to describe triangles.

Gripped - nay, seized - by a desire to see what the logo looked like, I needed to turn that into something the current TriD code can show me. I knew line3d could take a set of 4-point tuples to draw triangles if the 4th point was the same as the 1st. But how to turn points+indexes into that?

I often say that in PDL, the "right" solution to problems involves slices and dimension-mangling. This was no exception!

use PDL::Graphics::TriD;
use PDL::Graphics::TriD::Logo;
$p = $PDL::Graphics::TriD::Logo::POINTS; # dims: xyz, i
$i = $PDL::Graphics::TriD::Logo::FACES; # dims: i1to3, ntriangles
# 1: duplicate 0-th index onto end of each vector completing triangle
$i = $i->append($i->slice('0')); # change to i1to3to1
# 2: flatten indices, slice points with those, restore 4-tuples shape
$tri = $p->slice(':',$i->clump(-1))->splitdim(1,$i->dim(0));
line3d($tri); # visualise
[download]

Coda: the logo is just "PDL" in a serif font, given "depth" as if in a stick of rock.

I'm intending to update the VRML support to:

1. generalise that plus the OpenGL support of each specific thing (lines, points, etc) to go via an intermediate description to make this easy;
2. work at all;
3. switch it to use X3D;
4. use that to generate updated 3d demos for the PDL website.

If anyone wants to help, please say so!