a simpler test dataset exhibiting the same behavior is

np.array(
      [[[ 0.,  1],
        [ 0.,  2]],

       [[ 0.,  0],
        [ 0.,  1]]])

notebooks are attached

https://github.com/lukasheinrich/code-snippets/blob/master/voxels.ipynb
https://github.com/lukasheinrich/code-snippets/blob/master/voxels_custom.ipynb

Crossref #9559?

no, this is different. The implementation drops faces for adjoining voxels. Perhaps we can make this optional?

@WeatherGod yes that would be great. the internal faces are important if you want to do a 3d heatmap/ density plot.

I am putting together a PR for this feature (and might have found a bug in the original implementation, too), but I can't think of a good kwarg name for this. Any ideas?

maybe internal_faces ? with values True/False

Would unexposed_faces be clearer, perhaps?

to me internal_faces is more understandable. Also googling the term brings up similar problems, so maybe it's not a bad term?

http://meshlabstuff.blogspot.ch/2009/04/how-to-remove-internal-faces-with.html

ok, internal_faces it is.

just following up, what's the status on this -- anyways we can contribute?

@lukasheinrich , the PR is #9927

This was a deliberate decision in #6404, but it wasn't a principled one. There was a choice between

1. Drawing both faces in the same position, and letting z-fighting occur, making their color either a random function of viewing angle, or a function of draw order
2. Computing a "mixed" color for the two faces, and then drawing one. This is a little more work, and requires you to come up with a good mixing algorithm. Obviously for your single-color case, the algorithm is trivial.
3. Not drawing them at all

(1) could be fixed by drawing one-sided patches, but I'm not sure if matplotlib supports that.

(2) was more work that I was willing to invest for my problem (alpha was an afterthought), so I thought I'd leave it to someone more opinionated.

(3) was easy, so I went with it!

Note that you can use the approach here to force the culled faces to render, as well as avoiding z-fighting issues:

@eric-wieser yeah I saw that example, but it seems like a lot of bookkeeping/data-shuffling for a result that (to me) seems like a natural expectation. Would people still be interested in the work started in #9927 ?

I don't think #9927 is a good solution, because it overdraws two polygons of different colors in exactly the same spot

I do like the gapped look from the example you posted. Maybe this would be a good fit (perhaps with a adjustable gapsize kwarg?

That might be reasonable, with gapsize=None or maybe gapsize=0 being the current behavior. I think it should be a fraction of the voxel edge lengths, to scale well to the non-uniform cases.

Hi, Any progress on this? I was surprised to end up with something like this (where the two middle voxels are the same color):

If not, I might be interested in trying to work out the color blending based on https://en.wikipedia.org/wiki/Alpha_compositing#Alpha_blending Thanks!!

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