Implement ipyvtk

[akaszynski]

Overview

This PR implements #824 without changing much. I tried to clean up #824, but ended up needing a fresh start since our tests were consistently failing. Instead, this PR just adds in an interactor and adds an option for ipyvtk-simple rather than replacing panel (which is still useful). At this point, there's still no clear winner, but with some performance improvements in ipyvtk-simple Pull 13, I think it's up there. Plus, now users can write one set of code for my applications that use both jupyterlab and a standard python console.

We can move some of the other doc changes over once people have played around with this, but I was hoping on keeping this a "beta" feature for a bit until we work out the bugs/implementation rather than going all out and replacing anything.

@banesullivan, feel free to add back in some/all of your work in #824. I wanted to keep this change light and then consider greenlighting it in a minor release or two, so I figured keeping it fairly undocumented was reasonable.

Resolve #285, resolve #364

Additional Notes

There are some API changes, the largest being that we're always starting the interactive renderer (off or on screen). This has some big implications:

• Off screen renders on VTK 9.0 on Linux do not close, meaning that building docs results in a segfault on 9.0.X. You can get around this on doc building by simply building the docs twice; the first will encounter the segfault, the second will complete. On CI, I'm just limiting the max version to 8.1.2 until the next VTK release which includes a fix for this.
• Our documentation examples can finally include widgets, and it looks great, especially with the axes.
• No more checking if the interactive render has been created. Simplifies code.
• Unit testing on VTK 8.1.2 on Linux with the interactive render results in a plotter being rapidly flashed for each plotter unit test. It's annoying.

Overall, the changes result in a better plotter for the average/power user, so I think we should move forward with this. Flashing/doc building woes are something I can deal with until the next release of VTK.

[codecov]

Codecov Report

Merging #983 (051cdc1) into master (ba5ab42) will increase coverage by 2.04%.
The diff coverage is 89.56%.

@@            Coverage Diff             @@
##           master     #983      +/-   ##
==========================================
+ Coverage   87.10%   89.14%   +2.04%     
==========================================
  Files          36       37       +1     
  Lines        9165    11385    +2220     
==========================================
+ Hits         7983    10149    +2166     
- Misses       1182     1236      +54     

[banesullivan]

I will jump on this soon here - it is now a priority for me again. might be a day or two...

[banesullivan]

I'd like this to land on the next release (I know I've flipped-flopped on this a few times but I've converged on adding it)

[akaszynski]

I'd like this to land on the next release (I know I've flipped-flopped on this a few times but I've converged on adding it)

If we add it as a supplemental feature, there's no reason we can't add it.

[banesullivan]

@pyvista/developers, I added a change here that adds the vtkRenderWindowInteractor to all Plotters (on or off screen). This is the only notable change here and I'd like buy-in from folks before merging that.

Why? This makes it easy to support widgets when plotting with ipyvtk_simple and resolves #285. Plus it makes the API more consistent and we no longer have to check hasattr(self, 'iren') all over the place

[akaszynski]

82d4181 is causing the following failures locally on Ubuntu 18.04, Python 3.7, vtk==8.1.2:

FAILED tests/test_plotting.py::test_screenshot
FAILED tests/test_scraper.py::test_scraper
FAILED tests/test_plotting.py::test_save_screenshot[.png]
FAILED tests/test_plotting.py::test_save_screenshot[.jpg]
FAILED tests/test_plotting.py::test_save_screenshot[.tif]
FAILED tests/test_plotting.py::test_save_screenshot[.jpeg]
FAILED tests/test_plotting.py::test_save_screenshot[.tiff]
FAILED tests/test_plotting.py::test_save_screenshot[.bmp]

[akaszynski]

@pyvista/developers, this one is ready for review. It's nice to see axes on our docs:

[banesullivan]

LGTM! Though I played a significant part here so maybe I shouldn't give it approval

This has me pumped!! 🚀

[banesullivan]

One final thought. I think we should bring back the system flag on import that we had for panel and use it for ipyvtk_simple. This will make setting up the binder at playground.pyvista.org a bit easier.... will push a change momentarily