Three.js: Support basic mesh plots

[paulmasson]

This enhancement allows display of a black mesh grid on any surface by supplying the keyword mesh=True. To avoid z-fighting with the surface, the mesh is drawn twice, slightly above and slightly below the surface.

If the mesh alone is desired, it would be simple to hide the surface. The currently supported Boolean keyword does not allow this behavior, so some input would be needed as to best additional keyword practices. We could also allow setting the color and opacity of the grid separate from the material, but again input on appropriate keywords would be needed.

This ticket includes standardization of Line geometries in the Three.js template as well as additional cleanup and consistency. None of that should change existing behavior.

[paulmasson]

New commits:

​38b59f9

Support basic mesh plots

[egourgoulhon]

Thanks for this improvement! I've tested it on the examples with mesh=True of the 3D Graphics section of the reference manual. It looks nice!

There is one failing doctest:

sage -t --long --warn-long 78.5 src/sage/plot/plot3d/index_face_set.pyx
**********************************************************************
File "src/sage/plot/plot3d/index_face_set.pyx", line 1198, in sage.plot.plot3d.index_face_set.IndexFaceSet.json_repr
Failed example:
    S.json_repr(S.default_render_params())
Expected:
    ['{"vertices":[{"x":2,"y":0,"z":0},..., "face_colors":["#ff0000","#ff9900","#cbff00","#33ff00"], "opacity":1.0}']
Got:
    ['{"vertices":[{"x":2,"y":0,"z":0},{"x":0,"y":2,"z":0},{"x":0,"y":0,"z":2},{"x":0,"y":1,"z":1},{"x":1,"y":0,"z":1},{"x":1,"y":1,"z":0}], "faces":[[0,4,5],[3,4,5],[2,3,4],[1,3,5]], "faceColors":["#ff0000","#ff9900","#cbff00","#33ff00"], "opacity":1.0}']
**********************************************************************
1 item had failures:
   1 of  11 in sage.plot.plot3d.index_face_set.IndexFaceSet.json_repr
    [152 tests, 1 failure, 10.12 s]

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​f55a9ce

Fix doctest

[paulmasson]

Doctest fixed. Let's try to get this into 8.9.

[egourgoulhon]

Thanks!