Inaccurate docstring for the 'auto_update' argument of QtInteractor, BackgroundPlotter, and MultiPlotter

[p-j-smith]

The docstrings for these classes states:

    auto_update :
        Automatic update rate in seconds.  Useful for automatically
        updating the render window when actors are change without
        being automatically ``Modified``.

However, in the implementation of auto_update, the value of auto_update is raised to the power of -1:

twait = int((auto_update ** -1) * 1000.0)

meaning that auto_update actually specifies the number of updates per second (larger values = more updates), rather than the update rate in seconds (larger values = fewer updates).

I'm not sure if this is an issue with the docs or with the implementation?

[GuillaumeFavelier]

I agree with you @p-j-smith, it can be misleading. I think the documentation can be updated to clarify this.

cc @hoechenberger

[hoechenberger]

+1 this is confusing; in fact, @GuillaumeFavelier and I were tripped by this just a few days ago!