ManimCommunity/manim

opacity of Vector() and DashedVMobject(Vector) (Manim 0.17.3)

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#3220 opened on Apr 21, 2023

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 (3 comments) (0 reactions) (1 assignee)Python (17,820 stars) (1,378 forks)batch import
good first issueissue:bug

Description

Description of bug / unexpected behavior

The set stroke opacity and fill opacity is not obeyed for arrow heads - especially not when used within a DashedVMobject

Expected behavior

The opacity of the fill of the arrowhead is kept at 1.0 and not affected by setting the opacity value.

How to reproduce the issue

class arrowTransp(Scene):
    def construct(self):
        arr1 = Arrow(ORIGIN,[2,2,0], color=GREEN).shift(2*LEFT+UP)
        arr2 = arr1.copy().shift(DOWN).set_fill(opacity=0.4).set_stroke(opacity=0.4)
        arr3 = VGroup(DashedVMobject(arr2.copy().shift(DOWN))).set_fill(opacity=0.4, family=True).set_stroke(opacity=0.4, family=True)
        self.add(arr1,arr2,arr3)
        arr4 = Arrow(ORIGIN,[2,2,0], color=RED, tip_shape=StealthTip).shift(RIGHT+UP)
        arr5 = arr4.copy().shift(DOWN).set_fill(opacity=0.4).set_stroke(opacity=0.4)
        arr6 = VGroup(DashedVMobject(arr5.copy().shift(DOWN))).set_fill(opacity=0.4, family=True).set_stroke(opacity=0.4, family=True)
        self.add(arr4,arr5,arr6)

Additional media files

image

System specifications

Contributor guide

Tech stack
python
Domain
frontend
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.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Basic PythonFamiliarity with Manim rendering
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Look at the arrow head rendering in manim/mobject/geometry.py (Arrow class) and how opacity is applied in set fill and set stroke. The issue is that arrow head fill opacity remains at 1.0. Check the implementation of Vector and DashedVMobject to understand how they handle opacity. The provided code example shows the bug clearly; examine how these classes propagate opacity to sub mobjects.