always_redraw rendering only once

[dsvictor94]

Describe the bug

Testing the UpdatersExample I notice that the Brace do not rescale following the square as in the example video.

Reading the always_redraw code I could notice that a brand new mobject are created inside the updater callback and passed down to mob.become. But the become method clean the "old mob" updaters and copy the updaters from the "new mob" with has no updater. So, in the end, the redraw updater are deregistered.

Looking at the git log I think the bug was introduced at 0e45b41fea5f22d136f62f4af2e0d892e61a12ce when the match_updaters was added to the become method.

Code: https://3b1b.github.io/manim/getting_started/example_scenes.html#updatersexample

Wrong display or Error traceback:

https://user-images.githubusercontent.com/5621021/170176501-fc19b110-47fa-4184-8082-b9231dfc70b1.mp4

Additional context

Manim version: master branch at 07a8274cb17db54ce2deb2de28055186e914371c

[Eesha-Jain]

Hello! The code seems to work fine with this modification:

from manimlib import *

class UpdatersExample(Scene):
    def construct(self):
        #Create square
        square = Square()
        square.set_fill(BLUE_E, 1)

        #Create label to attach to side of square
        text, number = label = VGroup(
            Text("Width = "),
            DecimalNumber(
                0,
                show_ellipsis=True,
                num_decimal_places=2,
                include_sign=True
            )
        )

        brace = always_redraw(Brace, square, UP) #constantly redraw braces to match data
        always(label.next_to, brace, UP) #label is next to the brace
        always(brace.next_to, square, UP)
        f_always(number.set_value, square.get_width)
        f_always(brace.set_width, square.get_width)
        label.arrange(RIGHT)

        self.add(square, brace, label)

        #now change the width of the square
        self.play(
            square.animate.scale(2),
            rate_func=there_and_back,
            run_time=2
        )
        self.wait()
        self.play(
            square.animate.set_width(5, stretch=True),
            run_time=3
        )
        self.wait()
        self.play(
            square.animate.set_width(2, stretch=True),
            run_time=3
        )
        self.wait()

        #Update the label as the width of the square changes
        now = self.time
        w0 = square.get_width()
        square.add_updater(
            lambda m: m.set_width(w0 * math.cos(self.time - now))
        )
        self.wait(4 * PI)

[sherlcok314159]

Hi, you can just downgrade your manim to 1.5.0 to solve this problem.

pip install manimgl==1.5.0

[3b1b]

This should be fixed now.