[BUG] DashedLine computes num_dashes only once (on init)

[hmeine]

Description of bug / unexpected behavior

I am animating a DashedLine, using put_start_and_end_on() in an updater. This stretches the dashes, making them inconsistent with other DashedLines, when the length changes.

Expected behavior

I would like to have consistent dash geometries among all my dashed lines, so the number of dashes would have to be recomputed when I change the line length. I would be fine with calling an extra method in my updater, but right now the code in __init__ does not lend itself to being copied into an updater.

How to reproduce the issue

Code for reproducing the problem

class MovingDots(Scene):
    def construct(self):
        d1,d2=Dot(color=BLUE),Dot(color=GREEN)
        dg=VGroup(d1,d2).arrange(RIGHT,buff=1)
        l1=DashedLine(d1.get_center(),d2.get_center()).set_color(RED)
        x=ValueTracker(0)
        y=ValueTracker(0)
        d1.add_updater(lambda z: z.set_x(x.get_value()))
        d2.add_updater(lambda z: z.set_y(y.get_value()))
        l1.add_updater(lambda z: z.put_start_and_end_on(d1.get_center(),d2.get_center()))
        self.add(d1,d2,l1)
        self.play(x.animate.set_value(5))
        self.play(y.animate.set_value(4))
        self.wait()

Additional media files

Images/GIFs

MovingDots.mp4

Additional comments

My DashedLine has a number of properties, making it less attractive to use .become than in the above example. But I am new to manim, so maybe I am overlooking something.