Fixed Display Issue with Custom Axis Labels When renderer=opengl

[JinchuLi2002]

Closes #3069

Overview: What does this pull request change?

Fixes the issue causing axis labels being rendered incorrectly when renderer=opengl.

Typically when custom labels are applied (ex. LogScaling), NumberLine creates the labels by calling label_constructor with label_tex if label_tex is not a VMobject instance.

Issues arise when label_tex is of instance OpenGLVMobject. Since label_constructor is class MathTex by default which is supposed to take str as arguments, OpenGLMobject.__str__ is consequently called and passed into label_constructor.

Further Information and Comments

Example: Logarithmic Scaling

Test code

from manim import *
class LogScalingExample(Scene):
    def construct(self):
        ax = Axes(
            x_range=[0, 10, 1],
            y_range=[-2, 6, 1],
            tips=False,
            axis_config={"include_numbers": True},
            y_axis_config={"scaling": LogBase(custom_labels=True)},
        )

        # x_min must be > 0 because log is undefined at 0.
        graph = ax.plot(lambda x: x ** 2, x_range=[0.001, 10], use_smoothing=False)
        self.add(ax, graph)

with tempconfig({"quality": "high_quality", "preview": True, "renderer": "opengl"}):
    scene = LogScalingExample()
    scene.render()

Before

After

Example: Change Axis Label

Test code

from manim import *
class GetAxisLabelsExample(Scene):
    def construct(self):
        ax = Axes()
        labels = ax.get_axis_labels(
            Tex("x-axis").scale(0.7), Text("y-axis").scale(0.45)
        )
        self.add(ax, labels)

with tempconfig({"quality": "high_quality", "preview": True, "renderer": "opengl"}):
    scene = GetAxisLabelsExample()
    scene.render()

Before

After

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

[behackl]

LGTM