ManimCommunity/manim

VMobject inaccurately attributes width/height attrs to its bézier control points

Open

#3619 opened on Feb 15, 2024

View on GitHub
 (0 comments) (0 reactions) (0 assignees)Python (17,820 stars) (1,378 forks)batch import
good first issueissue:bug

Description

Description of bug / unexpected behavior

The VMobject width/height attributes are calculated using the points array which is actually the control points for the quadratic bézier curves. This is not very intuitive behavior for end-users.

Expected behavior

The VMobject width/height attributes should indicate the width/height of the physical curve, respectively.

How to reproduce the issue

class TestFail(Scene):
  def construct(self):
    c = Circle().scale(3)
    c.rotate(30*DEGREES)
    radius = c.width / 2
    l = Line().set_length(radius * 2).move_to(c)

    self.add(c, l)

image

Additional media files

https://discord.com/channels/581738731934056449/976376734935048223/1207665909871677500

Additional comments

Possibly related to this issue: #3344 This may be helpful for anyone fixing this issue in the future: https://stackoverflow.com/questions/2587751/an-algorithm-to-find-bounding-box-of-closed-bezier-curves

Contributor guide

Tech stack
python
Domain
backend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
PythonManimBézier curves
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65
Research direction
Investigate the VMobject class, specifically the width and height properties. The current implementation uses self.points which are control points. Refer to the StackOverflow link provided for an algorithm to compute the actual bounding box of a closed Bezier curve. Also examine the related issue #3344 for context. The fix should modify the width/height properties to return the actual bounding box dimensions of the rendered curve.