Fix 3D overlap when animating by checking Mobject family members recursively instead of self.mobjects

[MathItYT]

Motivation

As I mentioned in my previous pull request, I had problems when rendering VMobjects that overlap in 3D. The solution for that was making Scene aware of Mobject.z_index when grouping. Now, I had problems with animations, because Scene.begin_animations adds the mobject if it's not present in the scene, but it doesn't look recursively, so it could be present, but the scene adds it again, and that can be a bad behavior when submobjects had different z_index.

Proposed changes

• manimlib.scene.scene
• manimlib.animation.animation

Example scene

from manimlib import *

class ExampleScene(InteractiveScene):
    def construct(self) -> None:
        vg = VGroup(Square(), Circle().set_fill(opacity=0.5))
        vg[1].shift(0.5 * UP).set_z_index(1)
        self.add(*vg)
        self.play(GrowFromCenter(vg))

[3b1b]

In this case, it’s better to just have begin_animation check whether the animation’s mobject is in all the family data, not just the top level mobjects. The added runtime is negligible, and it'd be fixing an oversight that may produce issues elsewhere anyway.

I'll add a suggestion to this effect, which would basically boil down to replacing “self.mobjects” with “self.get_mobject_family_members()” in the check done inside begin_animations.

In general, it’s best not to have code handling scene structuring live outside of the Scene class itself.

[MathItYT]

@3b1b Ready

[3b1b]

Ah, you beat me to it. If this still fixes the issue you were facing, I'll go ahead and merge it.

Another option, if there is worry about too many calls to self.get_mobject_family_members() being innefficient, would be to write something like mobject_family = set(self.get_mobject_family_members()) at the top of the method, then check inclusion in that, and add the animation.mobject.get_family() to that set as you go.

[MathItYT]

Wdym?

[3b1b]

Eh, don't worry about it, I'll merge this.