put_start_and_end_on does not work with Arrow3D

[nathanielatom]

Description of bug / unexpected behavior

In 2D, put_start_and_end_on can be used to animate the tip of an arrow. In 3D the size/volume of the arrow appears to increase without bound, and also rotates much more than expected.

Expected behavior

The same behaviour as 2D but in 3D for an Arrow3D.

How to reproduce the issue

Code for reproducing the problem

```py from manim import * import numpy as np class ArrowAnimation(ThreeDScene): def construct(self): # Define the start and end points start_point = np.array([0, 0, 0]) framerate = 10 # Hz time = np.arange(0, 8, 1/framerate) period = 10 # s end_points = np.array([np.zeros_like(time), np.sin(2 * np.pi * time / period), np.cos(2 * np.pi * time / period)]).T # Create an arrow arrow = Arrow3D(start=start_point, end=end_points[0]) # end_points *= np.linalg.norm(arrow.get_vector()) / np.linalg.norm(arrow.end) # adjust end points so that the tip of the arrow is at the end point arrow.put_start_and_end_on(start_point, end_points[0]) # Create a traced path traced_path = TracedPath(arrow.get_end, stroke_color=ORANGE, stroke_width=2) # Add the arrow and traced path to the scene self.add(arrow, traced_path) # Animate the movement of the arrow for end_point in end_points: self.play( arrow.animate.put_start_and_end_on(start_point, end_point), rate_func=linear, run_time=1/framerate ) self.wait() ```

Additional media files

Images/GIFs

https://github.com/ManimCommunity/manim/assets/3137319/7ab8b408-38a6-408b-b1f2-d0e8e7feca5b

Working 2D Version

Code for reproducing the problem

```py from manim import * import numpy as np class ArrowAnimation(Scene): def construct(self): # Define the start and end points start_point = np.array([0, 0, 0]) framerate = 10 # Hz time = np.arange(0, 8, 1/framerate) period = 10 # s end_points = np.array([2 * np.sin(2 * np.pi * time / period), 2 * np.cos(2 * np.pi * time / period), np.zeros_like(time)]).T # Create an arrow arrow = Arrow(start=start_point, end=end_points[0]) # end_points *= np.linalg.norm(arrow.get_vector()) / np.linalg.norm(arrow.end) # adjust end points so that the tip of the arrow is at the end point arrow.put_start_and_end_on(start_point, end_points[0]) # Create a traced path traced_path = TracedPath(arrow.get_end, stroke_color=ORANGE, stroke_width=2) # Add the arrow and traced path to the scene self.add(arrow, traced_path) # Animate the movement of the arrow for end_point in end_points: self.play( arrow.animate.put_start_and_end_on(start_point, end_point), rate_func=linear, run_time=1/framerate ) self.wait() ```

Additional media files

Images/GIFs

https://github.com/ManimCommunity/manim/assets/3137319/52e66af5-dfdb-4181-8475-fbc954c54417

System specifications

System Details

- OS (with version, e.g., Windows 10 v2004 or macOS 10.15 (Catalina)): - RAM: - Python version (`python/py/python3 --version`): - Installed modules (provide output from `pip list`): ``` - MacOS 13.6.4 (22G513) (Ventura) - RAM: 16 GB - Python 3.9.10 - Pip modules: Package Version Editable project location --------------------------------- ------------------- ------------------------------------------------------------------------- absl-py 1.0.0 aiohttp 3.8.1 aiosignal 1.2.0 alabaster 0.7.12 alembic 1.7.6 altair 4.1.0 annoy 1.17.1 anyio 3.6.2 app-model 0.1.1 appdirs 1.4.4 appnope 0.1.2 APScheduler 3.7.0 argon2-cffi 20.1.0 arms-parser 0.2.4 /Users/Atom/Documents/AEL Backup/Aercoustics/code/arms-parser/source arrow 1.3.0 arviz 0.16.1 asl_bloch_sim 0.0.1 /Users/Atom/Library/CloudStorage/Dropbox/Skule/EECE597/source asteval 0.9.31 astropy 5.3.4 astropy-iers-data 0.2024.2.12.0.31.0 astroquery 0.4.2 asttokens 2.0.5 astunparse 1.6.3 async-generator 1.10 async-lru 2.0.4 async-timeout 4.0.2 attrs 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FFMPEG

Output of `ffmpeg -version`: ``` ffmpeg version 6.1 Copyright (c) 2000-2023 the FFmpeg developers built with Apple clang version 15.0.0 (clang-1500.1.0.2.5) configuration: --prefix=/usr/local/Cellar/ffmpeg/6.1-with-options_3 --enable-shared --cc=clang --host-cflags= --host-ldflags='-Wl,-ld_classic' --enable-gpl --enable-libaom --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-libsnappy --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-demuxer=dash --enable-opencl --enable-audiotoolbox --enable-videotoolbox --disable-htmlpages --enable-libtesseract --enable-libxvid --enable-libzimg libavutil 58. 29.100 / 58. 29.100 libavcodec 60. 31.102 / 60. 31.102 libavformat 60. 16.100 / 60. 16.100 libavdevice 60. 3.100 / 60. 3.100 libavfilter 9. 12.100 / 9. 12.100 libswscale 7. 5.100 / 7. 5.100 libswresample 4. 12.100 / 4. 12.100 libpostproc 57. 3.100 / 57. 3.100 ```

Additional comments

Even in 2D the put_start_and_end_on() method seems to use the line/vector (and ignores the triangle/cone) for the end point, whereas when initializing the Arrow class the end point does represent the tip of the triangle/cone.

[camburd2]

I will look into this.

[SirJamesClarkMaxwell]

good knew I have found a solution!!

[nathanielatom]

Care to elaborate?

[SirJamesClarkMaxwell]

Tommorow I will create a PR. The problem was in scaling. I had to add a get_start and get_end methods for cone and arrow3d classes.

[SirJamesClarkMaxwell]

This is the code I have added

[nathanielatom]

Cool thank you! I tried out the PR and it works beautifully.