add type annotations and docstrings for opengl_renderer.py

[arnaud-ma]

Overview: What does this pull request change?

Motivation and Explanation: Why and how do your changes improve the library?

For #3375

Links to added or changed documentation pages

Further Information and Comments

The typing revealed a bug in the get_texture_id method: it is passed a path (string), but throughout the function it is treated as if it were a PIL Image. No test triggers this call, and I did not find anything that could trigger it. To trigger it, there must be a mobject that has a shader in mobject.get_shader_wrapper_list() with a non-empty shader.texture.texture_paths. To fix this, the create_texture method open the path into a PIL Image.

Also, there are some uses of typing.cast. This is because of the implicit contracts "using OpenGLRenderer => the camera is an OpenGLCamera" and "using OpenGLRenderer => all mobjects are OpenGLMobject or OpenGLVMobject”. I think the proper way to deal with this would be to introduce generics in the Scene class, such as Scene[CameraType, MobjectType], and define protocol classes to bound these types. For example, for the camera:

class Camera(typing.Protocol): 
    minimal methods/attributes needed for a camera ...

_CameraType = typing.TypeVar("_CameraType", bound=Camera)

class Scene(typing.Generic[_CameraType]: 
     def __init__(self, ..., camera_class: type[_CameraType]):
         ...

but the cast seems quite reasonable compared to this complexity.

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested

[arnaud-ma]

CI tests failing only on mac due to font-related things seems really weird lol. I don't think this is related to this PR at all