Changelog / Overview

This adds a keyword shallow to OpenGLMobject.copy that controls whether a shallow or deep copy is returned. By default (and this is a change to the current behavior), a deep copy is returned.

Motivation

Returning a shallow mobject copy by default sometimes causes problems with (method) animations of complex mobjects, like Graph.change_layout (see the comment in #1202 for an example).

Testing Status

Well, this is a problem: given the lack of OpenGL tests, I'm not sure in how far this could degrade rendering speed. From what I've tried locally, I didn't really see a difference in the rendering times, but that's of course no guarantee.

Further Comments

This is just one potential solution to this problem. The more "courageous" way would be to always return a deep copy (as in the case of Mobject.copy and to delete the shallow copy code entirely.

Checklist

• I have read the Contributing Guidelines
• I have written a descriptive PR title (see top of PR template for examples)
• I have written a changelog entry for the PR or deem it unnecessary
• My new functions/classes either have a docstring or are private
• My new functions/classes have tests added and (optional) examples in the docs
• My new documentation builds, looks correctly formatted, and adds no additional build warnings

Reviewer Checklist

• The PR title is descriptive enough
• The PR is labeled correctly
• The changelog entry is completed if necessary
• Newly added functions/classes either have a docstring or are private
• Newly added functions/classes have tests added and (optional) examples in the docs
• Newly added documentation builds, looks correctly formatted, and adds no additional build warnings