Animations cannot be sequentially composed when working on the same object

[tobiasBora]

Description of bug / unexpected behavior

As far as I can, there is no way to easily (even sequentially) compose animations into a new animations, at least if the animations work on the same object. Indeed, I can't find any way to produce an animation anim3 that is the sequential composition of anim1 and anim2, as soon as anim1 and anim2 work an the same object. For instance, if we consider this code (see below for full usable code):

class Intro(Scene):
    def construct(self):
        libA = Rectangle(color=GREY, stroke_width=0, fill_opacity=1.0,fill_color=GRAY)
        libB = Circle(color=RED, stroke_width=0, fill_opacity=1.0,fill_color=RED)
        self.play(FadeIn(libA))
        # Make libB replace libA while rotating the elements
        libB.rotate(-PI/2, axis=(0,1,0))
        self.play(Rotate(libA, angle=PI/2, axis=(0,1,0)))
        self.play(FadeIn(libB, run_time=1/25),
                  FadeOut(libA, run_time=1/25)),
        self.play(Rotate(libB, angle=PI/2, axis=(0,1,0)))
        self.wait()

then the animation plays smoothly :

scriptoutput.mp4

but if I merge them all in a single animation (using AnimationGroup that seems to be the only method available as far as I see), then this fails:

from manim import *

class Intro(Scene):
    def construct(self):

        libA = Rectangle(color=GREY, stroke_width=0, fill_opacity=1.0,fill_color=GRAY)
        libB = Circle(color=RED, stroke_width=0, fill_opacity=1.0,fill_color=RED)
        self.play(FadeIn(libA))
        # Make libB replace libA while rotating the elements
        libB.rotate(-PI/2, axis=(0,1,0))
        ### This fails
        self.play(AnimationGroup(
            Rotate(libA, angle=PI/2, axis=(0,1,0)),
            AnimationGroup(
                FadeIn(libB, run_time=1/25),
                FadeOut(libA, run_time=1/25)),
            Rotate(libB, angle=PI/2, axis=(0,1,0)),
            lag_ratio=1))
        self.wait()

scriptoutput_.mp4

Note that I understand that applying multiple animations on the same object can be challenging if we apply them in parallel… but for sequential composition I don't see any conceptual difficulty.

Expected behavior

I expect animations to be composable trivially. Note that I do not want to use many self.play for many reasons:

1. first, the animation is supposed to be abstracted into a library, and asking the user to manually loop over a list of animations is really dirty, I would prefer the user to write only self.play(myobject.turn_into(my_otherobject)).
2. then, it is harder to control the easing curves of animations played composed with multiple self.play as the easing curve would be to be split into multiple pieces
3. it is even harder to compose this animation with another (independent) animation in parallel, as we would need to cut the parallel animation into multiple sub-animations that last the same time as the sub-animations… ugly.

How to reproduce the issue

Code for reproducing the problem

from manim import *

class Intro(Scene):
    def construct(self):

        libA = Rectangle(color=GREY, stroke_width=0, fill_opacity=1.0,fill_color=GRAY)
        libB = Circle(color=RED, stroke_width=0, fill_opacity=1.0,fill_color=RED)
        self.play(FadeIn(libA))
        # Make libB replace libA while rotating the elements
        libB.rotate(-PI/2, axis=(0,1,0))
        ### This fails
        self.play(AnimationGroup(
            Rotate(libA, angle=PI/2, axis=(0,1,0)),
            AnimationGroup(
                FadeIn(libB, run_time=1/25),
                FadeOut(libA, run_time=1/25)),
            Rotate(libB, angle=PI/2, axis=(0,1,0)),
            lag_ratio=1))
        self.wait()

You might also want to see a related discussion on discord https://discord.com/channels/581738731934056449/1142285601232662538

[vaclavblazej]

@tobiasBora Is Succession what you are searching for?

[tobiasBora]

Thanks. Succession seems to be no better than GroupAnimation(…, lag_ration=1) in my tests. However, dudewaldo4 found a workaround: wrap every animation in a AnimationGroup:

from manim import *
config.background_color = WHITE

class Intro(ThreeDScene):
    def construct(self):
        Mobject.set_default(color=BLACK)
        libA = VGroup(Rectangle(color=BLUE), MathTex(r"\sqrt{\Theta}"))
        libB = VGroup(Rectangle(color=RED), MathTex(r"\sqrt{\Delta}"))
        self.play(FadeIn(libA))
        libB.rotate(-PI/2, axis=(0,1,0))
        self.play(Succession(
            AnimationGroup(Rotate(libA, angle=PI/2, axis=(0,1,0),rate_func=rate_functions.linear),run_time=.5),
            AnimationGroup(
                FadeIn(libB, run_time=1/25),
                FadeOut(libA, run_time=1/25)),
            # This also fails:
            # AnimationGroup(
            #     Transform(libA, libB, run_time=1/25)),
            AnimationGroup(Rotate(libB, angle=PI/2, axis=(0,1,0),rate_func=rate_functions.linear), run_time=.5),
            rate_func=rate_functions.ease_in_out_cubic
        ))

        self.wait()

However, you can still see a weird thing, with a red line appearing in between (seems like the last item that is added before the actual animation starts):

scriptoutput.mp4

if you try with

class Intro(ThreeDScene):
    def construct(self):
        Mobject.set_default(color=BLACK)
        libA = VGroup(Rectangle(color=BLUE), MathTex(r"\sqrt{\Theta}"))
        libB = VGroup(Rectangle(color=RED), MathTex(r"\sqrt{\Delta}"))
        self.play(FadeIn(libA))
        # Make libB replace libA while rotating the elements
        libB.rotate(-PI/2, axis=(0,1,0))
        self.play(Succession(
            AnimationGroup(Rotate(libA, angle=PI/2, axis=(0,1,0),rate_func=rate_functions.linear),run_time=.5),
            # This fails (libB is visible from the start):
            # AnimationGroup(
            #     FadeIn(libB, run_time=1/25),
            #     FadeOut(libA, run_time=1/25)),
            # # This also fails:
            AnimationGroup(
                Transform(libA, libB, run_time=1/25)),
            AnimationGroup(Rotate(libB, angle=PI/2, axis=(0,1,0),rate_func=rate_functions.linear), run_time=.5),
            rate_func=rate_functions.ease_in_out_cubic
        ))

        self.wait()

the result is even more weird as the line stays forever.

[MrDiver]

Currently with the Animation system there is sadly no good way of doing this because every Animations assumes it's the only owner of a Mobject. This will be resolved in a future release of Manim where we have reworked the Animations