Pyvista

New Features

- New depth mapping feature for the rendering window (see 369 and 368)
- New layout options for subplotting (see 380). Many thanks to marcomusy
- Anti-aliasing features (see 365)
- Background color and number of colors are now settable for the scalar bar (see 370)
- New relaxation parameter for the `PolyData.smooth` filter (see 374)
- Major overhaul of the widget tools to improve performance (see 376)
- New `shallow_copy` and `deep_copy` methods (see 377)
- Improve default options for texture mapping
- Wrapped the `vtkTexture` class
- Enable use of `edl` keyword argument for eye dome lighting in the `.plot()` function.
- New shortcuts for the `point_data_to_cell_data()` and `cell_data_to_point_data()` filters as `ptc()` and `ctp()` respectively.

Bug Fixes

- Minor improvements for supporting Panel (ref 268)
- Fix `BackgroundPlotter` menu bar on some Linux platforms (see 371)
- Much cleanup, typos, etc., fixed by marcomusy in 380
- Much PEP8 cleanup inside the library

There was a serious bug with the plane widget that somehow made it in the last release. This patch release resolves that issue and adds support for `MultiBlock` datasets with the widgets.

New Features

- Add full support for widgets in the rendering scene! (See 360)
- Box widget - Create a box in 3D space. Includes a convenience method for clipping meshes
- Plane widget - Create an implicit plane in 3D space. Includes a convenience method for clipping and slicing meshes
- Slider widget - Add a slider bar to the render window. Includes a convenience method for thresholding meshes
- Line widget - Create and orient a line in 3D space.
- Point picking (see 362)
- Single point picking on meshes and in 3D space
- Trace lines across meshes using a geodesic path
- Trace lines through a scene by picking points on meshes or in 3D space
- Trace out horizon surfaces
- Wrap the `vtkTable` class (see 274 and the new `pyvista.Table` class)
- Add a structured grid cylinder helper method (see `pyvista.CylinderStructured`) which works creates a `pyvista.StructuredGrid` mesh in the shape of a cylinder.
- New `.ribbon()` filter for `PolyData` objects - create surfaces (“ribbons”) from lines
- `interpolate_befor_map` is now set too `True` as default (see 363 and [this example](https://docs.pyvista.org/examples/02-plot/interpolate-before-map.html) for details)


Bug Fixes

- Resolve issues with the `lines_from_points` helper methods (see 357)
- Fix an issue when fetching null points on datasets

Exciting New Features

- Labeled scalar bars!!! 🎉 (See 348 and [this example](https://docs.pyvista.org/examples/02-plot/scalar-bars.html)) Now arrays with strings categories can be color mapped
- Ability to clip a mesh using the surface of another mesh (see 354 and [this example](https://docs.pyvista.org/examples/01-filter/clipping.html#clip-with-surface))
- Parallel projection (see 337)
- New MCubes reader (`.tri` files)
- New cell quality and gradient filters (see 354)
- Implement the `+` operator to support all PyVista meshes


Bug Fixes
- Subplotting borders fixed
- Handle arrays with no name (see 306)
- Fix the `fly_to` method
- Typos and grammar fixed in the example gallery - huge thanks to JasonTlin
- Fixed issue with the `+` operator that appeared in `v0.21.3`
- Clear the menu bar for the BackgroundPlotter when closing on Mac OS (see 350)

This release is primarily full of bug fixes and general cleanup around the filters and plotting methods.

Bug Fixes

- Fix points ordering issue with gridded datasets
- Fix issues with overlapping colorers (see 319)
- Fix rare bug when scalars are the wrong size
- Handle `panel` runtime errors on import (see 322)
- Fix `smooth_shading` issue for non-`PolyData` datasets
- Fix subplot indexing issues (see 346)


Changes

- Memory footprint is improved (see 338)
- `panel` notebook rendering is now off by default
- New downloadable examples!
- Filters were overhauled into their own module and generalized across datasets (see 323)
- Improved control over axes widgets (see 334 and 342)
- Improvements to `add_mesh` and `add_volume` docstrings
- Deprecate `BasePlotter.plot` (see 341)
- Enable use of poly lines with `PolyData` (see 344)
- Add more lighting controls (see 343)

- Fix 32bit Python on 64bit OS ID type issues (see 316)
- `BackgroundPlotter` changes:
- Window title (see 305)
- Add callback support (see 304)
- Fix closing issues (see 315)
- Add offscreen support (see 309)
- Fix window resizing issue (see 315)
- Fix typos
- Add `null_value` support for the `.interpolate` filter
- Replace AppVeyor with Azure Pipelines for Windows testing (see 317)
- Add more special array names to the exclusion list for active scalars (see 307)
- Update docstring for `.add_text` to detail how return type can vary (see 312)