GR: add support for mesh3d

[t-bltg]

Add GR support for mesh3d since, for now, GR does not support drawing arbitrary points using a triangle connectivity array.
The error check code was copied from the pgfplotsx backend: https://github.com/JuliaPlots/Plots.jl/blob/master/src/backends/pgfplotsx.jl

The test for this case already exists here as example 47, and is run e.g. for pgfplotsx: https://docs.juliaplots.org/latest/generated/pgfplotsx/#pgfplotsx-ref47.

Needs JuliaPlots/RecipesPipeline.jl#90 patch.

Output of example 47

• generate ref47.png for GR
  Add ref47 for Plots.jl/pull/3612 PlotReferenceImages.jl#101

Linked #392

[BeastyBlacksmith]

This is missing the faces of the triangles though. Also some legend figure would be good.

[t-bltg]

This is missing the faces of the triangles though.

All right. But I would like to be able do disable faces via an option ...

Also some legend figure would be good.

OK I will change the example then.

[BeastyBlacksmith]

You could also add a warning, that the GR backend doesn't support 3D mesh's with faces at the moment

[codecov]

Codecov Report

Merging #3612 (ed8fb4d) into master (ef93aa8) will decrease coverage by 1.53%.
The diff coverage is 35.23%.

❗ Current head ed8fb4d differs from pull request most recent head f5e6ae9. Consider uploading reports for the commit f5e6ae9 to get more accurate results

@@            Coverage Diff             @@
##           master    #3612      +/-   ##
==========================================
- Coverage   65.19%   63.66%   -1.54%     
==========================================
  Files          27       28       +1     
  Lines        6663     6885     +222     
==========================================
+ Hits         4344     4383      +39     
- Misses       2319     2502     +183     

Impacted Files	Coverage Δ
src/backends.jl	61.06% <0.00%> (-2.25%)	⬇️
src/backends/gaston.jl	0.00% <0.00%> (ø)
src/examples.jl	61.76% <ø> (ø)
src/utils.jl	52.53% <54.54%> (-0.05%)	⬇️
src/backends/gr.jl	89.05% <88.09%> (+0.04%)	⬆️
src/axes.jl	84.75% <100.00%> (+0.72%)	⬆️
src/backends/pgfplotsx.jl	60.94% <100.00%> (ø)
src/init.jl	100.00% <100.00%> (ø)
src/layouts.jl	67.96% <100.00%> (-0.60%)	⬇️
src/pipeline.jl	89.63% <100.00%> (+0.51%)	⬆️
... and 6 more

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[briederer]

Quick question.
Could this mesh3d function be used to get a nicely working histogram3d (#3379)?
I started a PR (#3507) a few months ago but currently don't have any time to work on that 😕

So maybe my initial work on that could be finished with that PR being merged.

[t-bltg]

Quick question.
Could this mesh3d function be used to get a nicely working histogram3d (#3379)?
I started a PR (#3507) a few months ago but currently don't have any time to work on that confused

So maybe my initial work on that could be finished with that PR being merged.

I don't think so, since this is only for triangles, your vertical bars would be ugly ! Also, this is only for the GR backend.

However you mentioned in #3507 (comment) that surface didn't have a mesh option.

I've merged this PR which allows to use GR options when using surface, see the examples at #3591

Thinking out loud, maybe you can use:

surface(...)
surface!(..., display_option=GR.OPTION_SHADED_MESH)  # for a mesh on top of the previous plot ?

Is that of any help ?

[briederer]

Thanks for the suggestions.
I somehow completely missed that this PR is only for triangles. 😅

I'll think about your suggestions, and if you happen to have another good idea comment on my PR #3507.

[t-bltg]

@BeastyBlacksmith, if you don't see anything against, can I merge this ?