Add add_ruler to BasePlotter

[MatthewFlamm]

Overview

This PR adds add_ruler functionality to the plotter using vtkAxisActor2D.

This is useful for adding customizable scale or measurements to the scene.

Edit: Updated image using flip_range.

TODO:

• tests

[MatthewFlamm]

I used reset_camera=True here, but it doesn't seem to do anything. If the users picks pointa and pointb to be outside the normal viewing area, it won't resize based on the choice here. Probably because of the 2D overlay nature of this actor.

If this can't be fixed, we can just put in a note in the docstring about this.

[akaszynski]

One way you could work around this is adding fictitious points and then removing them to get the camera to increase the bounds. If this is out of the scope of the PR or you feel it's too complex, you can just add a note in the docstring.

[MatthewFlamm]

I tried this without success, so I added in a note.

tmp_points = pyvista.PolyData([pointa, pointb])
tmp_actor = self.add_mesh(tmp_points, reset_camera=True)
self.remove_actor(tmp_actor, reset_camera=False)

[MatthewFlamm]

If I get rid of self.remove_actor then the camera does reset as expected, but then it leaves behind the fictituous points. It seems that reset_camera=False isn't working quite correctly in this case?

[codecov]

Codecov Report

Merging #2531 (1850aca) into main (b6ab604) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

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##             main    #2531      +/-   ##
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- Coverage   93.72%   93.71%   -0.01%     
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  Files          75       75              
  Lines       16116    16145      +29     
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+ Hits        15105    15131      +26     
- Misses       1011     1014       +3     

[MatthewFlamm]

I had to use the functionality in vtkLegendScaleActor to wrap my head around how to correctly set the start and stop positions for this actor. This may be helpful if anyone wants to review that portion of the implementation.

I considered exposing the AdjustLabels and RulerMode options, but I found the behavior to be hard to understand. But this may be based on my lack of understanding on how they work.

[akaszynski]

This is good as-is; you can choose to supplement the methods with docstrings for the limitations of the vtkAxisActor2D.