[BUG] manim-slides gets confused with multiple scenes

[ccoors]

Description

When using multiple scenes, manim-slides appears to get confused with slide-order and replaying animations.

Take the following example:

from manim import *
from manim_slides import Slide


class Part1(Slide):
    def construct(self):
        self.add(MarkupText("Part 1").shift(3 * UP))
        counter = DecimalNumber().shift(2 * UP)
        self.add(counter)
        square = Square(color=BLUE, fill_opacity=1)
        self.play(square.animate.shift(LEFT))
        self.next_slide()

        counter.set_value(1)
        self.play(square.animate.scale(0.3))
        self.next_slide()


class Part2(Slide):
    def construct(self):
        self.add(MarkupText("Part 2").shift(3 * UP))
        counter = DecimalNumber().shift(2 * UP)
        self.add(counter)
        square = Square(color=RED, fill_opacity=1)
        self.play(square.animate.shift(3 * RIGHT))
        counter.set_value(1)
        self.play(square.animate.set_color(GRAY))
        self.next_slide()

        counter.set_value(2)
        self.play(square.animate.scale(1.3))
        self.next_slide()

I am running these commands:

$ manim -qh bug.py Part1 Part2
$ manim-slides Part1 Part2

Steps to reproduce weird behavior

1. Slideshow starts normally, blue square is shown moving left
2. Press right arrow, Square shrinks. Immediately afterwards, Part2 starts (even though there is a self.next_slide() in the code that should pause)
3. After the red square moved right and turned gray, press the left arrow key. Part1 starts from the beginning, not from animation 2
4. Press the right arrow once, the blue square shrinks and only the second animation from the first section of Part2 is shown (not the square moving right, but only the square turning gray)

Additional weird behavior

Remove the first self.next_slide() from Part1, leaving only the one at the end. Press the left arrow key while Part2 plays and observe the following Traceback:

Traceback (most recent call last):
  File "/home/.../venv/lib/python3.11/site-packages/manim_slides/present.py", line 445, in run
    self.handle_key()
  File "/home/.../venv/lib/python3.11/site-packages/manim_slides/present.py", line 564, in handle_key
    self.current_presentation.load_last_slide()
  File "/home/.../venv/lib/python3.11/site-packages/manim_slides/present.py", line 275, in load_last_slide
    self.current_slide_index >= 0
AssertionError: Slides should be at list of a least two elements

Sorry if this issue is a bit confusing, but separating it into multiple issues would probably not be helping.

Version

manim-slides, version 4.14.0, used with Manim Community v0.17.3

Platform

Linux

Screenshots

No response

Additional information

Possibly related to #161?

[jeertmans]

Oh, nice bug you found here! I think this is caused by me trying to optimize everything with a "one-scene-presentation" in mind, introducing some bugs when multiple presentations are played.

After a quick look, the fix does not look straightforward. I am planning to rewrite the Video player, to add audio support, so this might take a bit more time :'-)

Regarding the ordering of animations, their numbering, and so on, this might also be part of that rework!

I'm sorry for not having a solution at the moment (or at least not one that comes to my mind).

[jeertmans]

Hi @ccoors, I think I have addressed this issue in #234 :-)

I am planning on releasing this fix with other improvements in v4.15, later today

[ccoors]

Thanks, I'll check it out :) Btw, in the meantime I built manim-mpv-presentation for my purposes, a very very lightweight presentation player thingy for Manim which works surprisingly well.

[jeertmans]

Nice, I see it uses the sections feature from Manim! I have long hesitated to use it too, but it is currently not available with ManimGL :/