Fixed :meth:.OpenGLVMobject.pointwise_become_partial to improve stroke rendering

[MrDiver]

Overview: What does this pull request change?

Fixing the stroke rendering of the opengl mobjects by porting the curve functions over to them and then optimizing the code again with the newly added features

• opengl_vectorized_object
  • fixed implementation of pointwise_become_partial (ported from vectorized_mobject)

Before vs After

Before	After

Test Scene Code

class DashedVMobjectExample(Scene):
    def construct(self):
        r = 0.5

        top_row = VGroup()  # Increasing num_dashes
        for dashes in range(1, 12):
            circ = DashedVMobject(Circle(radius=r, color=WHITE), num_dashes=dashes)
            top_row.add(circ)

        middle_row = VGroup()  # Increasing dashed_ratio
        for ratio in np.arange(1 / 11, 1, 1 / 11):
            circ = DashedVMobject(
                Circle(radius=r, color=WHITE), dashed_ratio=ratio
            )
            middle_row.add(circ)

        func1 = FunctionGraph(lambda t: t**5,[-1,1],color=WHITE)
        func_even = DashedVMobject(func1,num_dashes=6,equal_lengths=True)
        func_stretched = DashedVMobject(func1, num_dashes=6, equal_lengths=False)
        bottom_row = VGroup(func_even,func_stretched)


        top_row.arrange(buff=0.3)
        middle_row.arrange()
        bottom_row.arrange(buff=1)
        everything = VGroup(top_row, middle_row, bottom_row).arrange(DOWN, buff=1)
        self.add(everything)

class SimpleGLTestStill(Scene):
    def construct(self):
        square = Square(side_length=2)
        square.set_fill(RED, opacity=0.3)
        square.rotate(PI / 4)
        square.set_stroke(WHITE, width=2)

        dashed = DashedVMobject(square.copy().rotate(PI/4).scale(2), num_dashes=20, equal_lengths=True)
        dashed.set_fill(GREEN)

        self.add(DashedLine((-3.5,-3,0),(-3.5,3,0)))
        self.add(DashedLine((-3,3,0),(-3,-3,0)))
        self.add(DashedLine((-3,3.5,0),(3,3.5,0)))
        self.add(DashedLine((-2,3,0),(2,3,0)))

        self.add(Line((3.5,-3,0),(3.5,3,0)))
        self.add(Line((3,3,0),(3,-3,0)))
        self.add(Line((-3,-3.5,0),(3,-3.5,0)))
        self.add(Line((-2,-3,0),(2,-3,0)))

        self.add(DashedVMobject(Circle().scale(2), num_dashes=20, equal_lengths=False))
        self.add(DashedVMobject(Circle().scale(1.5), num_dashes=20, equal_lengths=True))
        self.add(square, dashed)
        cube_mesh = Cube(side_length=2)
        self.add(cube_mesh.rotate(PI/4, axis=UP).rotate(PI/4, axis=LEFT).scale(0.5).set_stroke(WHITE,width=2))

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

Futher improves rendering compatibility with OpenGL

Depends on

• Fixed missing get_nth_curve_length_pieces method of :class:.OpenGLVMobject #2707

Archive

Persisting problem

Overlapping points produce gaps in a curve. It would be good if the mobject didn't need all the redundant points! But if we change the implementation to be similar to vectorized_mobject then the interpolation function will not work anymore. There needs to be a way to interpolate between mobjects with different amounts of points!

Reality	Expected

Temporary solution

I switched the order in which the points appear such that they produce no gaps but also do not produce errors in an animation or triangulation step.

Solution

Porting over pointwise_become_partial from Mobject into OpenGLMobject

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

[k4pran]

This looks great thank you very much. I don't know the code well so hopefully someone else can also review, but I tested it locally and the examples you provided work well. I was also playing around with some other existing examples and they also look good.

[MrDiver]

Still breaks a lot. The Animation system needs a deeper rewrite than this to be comparable to the cairo rendering.

[MrDiver]

Now ready to be reviewed and potentially merged!

[MrDiver]

get_bezier_tuples_from_points might be implemented with np.reshape instead of creating a new list. This assures no conversion between numpy and normal python is taking place when remapping which makes it a lot faster!