#4945·manim

Line object bending in unexpected ways during animation

Author: wuerfelfreakCreated Aug 20, 2026Updated Aug 21, 2026

Description of bug / unexpected behavior

Under specific circumstances a Line object can bend during an animation in unexpected ways despite path_arc=0.

Expected behavior

A Line object should not have any curvature when path_arc=0.

How to reproduce the issue

Code for reproducing the problem

This issue came up in this animation:

from manim import *

class Example(Scene):
    def construct(self):
        t = ValueTracker(0.1 * PI)
        line = Line(end=(1,0,0))
        line.add_updater(lambda m: m.put_start_and_end_on(
                (3.4 , 0, 0),
                (3.4 + 1.5*np.cos(t.get_value()), 1.5*np.cos(t.get_value()),0)
            )
        )

        self.add(line)

        self.play(
            t.animate.set_value(12.1 * PI),
            run_time=6,
            rate_func=linear,
        )

which was rendered with this command

manim -pql --fps=20 test.py Example

I already tried to reduce it to a minimal example. Different quality and frame rate settings produce different curvatures. The shift in x-direction also influences the curvature.

Additional media files

Images/GIFs

https://github.com/user-attachments/assets/e3921c3d-5a10-4505-98ad-93ee154affe9

Logs

Terminal output

Manim Community v0.21.0

[08/20/26 09:54:09] DEBUG    Hashing ...                                                         hashing.py:443
                    DEBUG    Hashing done in 0.001507 s.                                         hashing.py:462
                    DEBUG    Hash generated :  1594855120_2984155222_1892506515                  hashing.py:463
                    DEBUG    List of the first few animation hashes of the scene:         cairo_renderer.py:101
                             ['1594855120_2984155222_1892506515']                                              
                    INFO     Animation 0 : Partial movie file written in               scene_file_writer.py:192
                             '/home/[...]/wiggly_line_test                         
                             /media/videos/test/480p20/partial_movie_files/Example/159                         
                             4855120_2984155222_1892506515.mp4'                                                
                    INFO     Combining to Movie file.                                  scene_file_writer.py:952
                    DEBUG    Partial movie files to combine (1 files):                 scene_file_writer.py:834
                             ['/home/[...]/wiggly_line_tes                         
                             t/media/videos/test/480p20/partial_movie_files/Example/15                         
                             94855120_2984155222_1892506515.mp4']                                              
                    INFO                                                              scene_file_writer.py:1103
                             File ready at                                                                     
                             '/home/[...]/wiggly_line_tes                          
                             t/media/videos/test/480p20/Example.mp4'                                           
                                                                                                               
                    INFO     Rendered Example                                                      scene.py:290
                             Played 1 animations

System specifications

System Details

Ubuntu 24.04.4
Python 3.12.3

Source: ManimCommunity/manim

View original on GitHub View discussion on GitHub