Resetting the opacity of NumberLine numbers doesn't animate smoothly

[ericrowland]

Description of bug / unexpected behavior

Create a number line with numbers. Animate a change in the opacity of the numbers, accessed with NumberLine.numbers. The opacity changes abruptly rather than smoothly.

Smooth opacity change can be obtained by putting the numbers in a VGroup, but then the axis disappears.

Expected behavior

The opacity should change smoothly without removing the axis.

How to reproduce the issue

Code for reproducing the problem

from manim import *

class numberline(Scene):
    def construct(self):

        abrupt_opacity = Tex("Opacity changes abruptly:").shift(UP)
        number_line = NumberLine(include_numbers = True)
        self.add(abrupt_opacity, number_line)
        self.wait(1)
        self.play(
            number_line.numbers.animate.set_fill(opacity = .2)
        )
        self.wait(1)
        self.remove(abrupt_opacity, number_line)

        self.wait(1)

        axis_disappers = Tex("Axis disappears:").shift(UP)
        number_line = NumberLine(include_numbers = True)
        self.add(axis_disappers, number_line)
        self.wait(1)
        self.play(
            VGroup(*number_line.numbers).animate.set_fill(opacity = .2)
        )
        self.wait(1)

Additional media files

Images/GIFs

numberline.mp4

Logs

Terminal output

PASTE HERE OR PROVIDE LINK TO https://pastebin.com/ OR SIMILAR

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):

PASTE HERE

LaTeX details

• LaTeX distribution (e.g. TeX Live 2020):
• Installed LaTeX packages:

FFMPEG

Output of ffmpeg -version:

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Additional comments

[Aljumaily]

Use number_line.animate.... instead of number_line.numbers.animate..... Just for fun, the second approach is also fixed by using ###VGroup(*number_line).animate....

from manim import *

class numberline(Scene):
    def construct(self):

        abrupt_opacity = Tex("Opacity changes abruptly:").shift(UP)
        number_line = NumberLine(include_numbers = True)
        self.add(abrupt_opacity, number_line)
        self.wait(1)
        self.play(
            number_line.animate.set_fill(opacity = .2)
        )
        self.wait(1)
        self.remove(abrupt_opacity, number_line)

        self.wait(1)

        axis_disappers = Tex("Axis disappears:").shift(UP)
        number_line = NumberLine(include_numbers = True)
        self.add(axis_disappers, number_line)
        self.wait(1)
        self.play(
            VGroup(*number_line).animate.set_fill(opacity = .2)
        )
        self.wait(1)

numberline.mp4

[ericrowland]

Thanks for the workaround. But number_line.numbers.animate.set_fill(opacity = .2) should work, right?

[Aljumaily]

I tested it again and your suggestion didn't work. However, if what you suggested should work, I don't know... I am a simple guy trying to learn Manim. The experts might share their suggestions regarding that ☺️.

[ericrowland]

Yes, that's what I mean. The workaround is great, but I believe it is still a bug that number_line.numbers.animate.set_fill(opacity = .2) does not work as expected. Thanks!