[BUG] skip_animations causes ValueError: Cannot merge an empty list of files!

[Rapsssito]

Terms

• Checked the existing issues and discussions to see if my issue had not already been reported;
• Checked the frequently asked questions;
• Read the installation instructions;
• Created a virtual environment in which I can reproduce my bug;

Describe the issue

Passing skip_animations=True to self.next_slide() raises the exception ValueError: Cannot merge an empty list of files! from manim_slides\slide\manim.py:136 > manim_slides\slide\base.py:526 > manim-slides\manim_slides\utils.py:68.

skip_animations=True is really useful for implementing long chained animations. I saw the PR #155, but maybe it breaks if all the animations from the slide are skipped?

Command

manim-slides render example.py MWE

Issue Type

Other

Python version

Python 3.12.7

Python environment

Manim Slides version: 5.2.0
Python executable: AppData\Local\Programs\Python\Python312\python.exe
Manim bindings:
        manim (version: 0.18.1)
        manimgl not found
Qt API: pyqt5 (version: 5.15.2)

What is your platform?

Windows

Other platform

No response

Manim Slides Python code

from manim import *

from manim_slides import *

class MWE(Slide):
    def construct(self):
        # Add a square and a circle
        square = Square()
        self.play(Create(square))
        self.next_slide(skip_animations=True)
        circle = Circle()
        self.play(Create(circle))

Relevant log output

No response

Screenshots

No response

Additional information

No response

Recommended fix or suggestions

An option could be adding a placeholder video instead of the slide if the slide does not contain any animations.

[jeertmans]

Hi @Rapsssito, thanks for reporting this bug!

Indeed, #155 introduced support for skipping animations rendering, but it was meant to be used from the terminal with the -nx,y option, that renders animations from number x to number y, if I remember correctly. The issue arises when you skip rendering part of a slide, I think.

I don't think self.next_section(skip_animations=True) already existed at that time. But it could be a nice feature to support this! It could be as simple as storing a new skip_animations flag in

manim-slides/manim_slides/config.py

Lines 217 to 221 in 541b175

	class PreSlideConfig(BaseSlideConfig):
	"""Slide config to be used prior to rendering."""
	start_animation: int
	end_animation: int

and skip current iteration (with continue) in

manim-slides/manim_slides/slide/base.py

Lines 517 to 545 in 541b175

	for pre_slide_config in tqdm(
	self._slides,
	desc=f"Concatenating animation files to '{scene_files_folder}' and generating reversed animations",
	leave=self._leave_progress_bar,
	ascii=True if platform.system() == "Windows" else None,
	disable=not self._show_progress_bar,
	):
	slide_files = files[pre_slide_config.slides_slice]
	file = merge_basenames(slide_files)
	dst_file = scene_files_folder / file.name
	rev_file = scene_files_folder / f"{file.stem}_reversed{file.suffix}"
	# We only concat animations if it was not present
	if not use_cache or not dst_file.exists():
	concatenate_video_files(slide_files, dst_file)
	# We only reverse video if it was not present
	if not use_cache or not rev_file.exists():
	if skip_reversing:
	rev_file = dst_file
	else:
	reverse_video_file(dst_file, rev_file)
	slides.append(
	SlideConfig.from_pre_slide_config_and_files(
	pre_slide_config, dst_file, rev_file
	)
	)

if pre_slide_config.skip_animations is True.

I'll mark this as a good first issue, as I think it is relatively easy to solve.