Deprecate different signatures for updaters

[leotrs]

The problem

This is part of mobject:mobject.update() method:

manim/manim/mobject/mobject.py

Lines 155 to 163 in 5054700

	def update(self, dt=0, recursive=True):
	if self.updating_suspended:
	return self
	for updater in self.updaters:
	parameters = get_parameters(updater)
	if "dt" in parameters:
	updater(self, dt)
	else:
	updater(self)

L159 fetches the parameters of each updater, each time the object is updated, which may occur multiple times in a single animation, let alone a whole scene. Fetching the parameter list makes use of the inspect library, which is not the fastest thing in the world.

I think this is super unnecessary and adding a lot of overhead. This checking of the parameter list is done so that each updater can be called appropriately: either updater(self, dt), or just updater(self). The gain in convenience for the end user seems very small in comparison to the overhead that this incurs in.

A possible fix

My suggestion is that we should just make each updater always accept two arguments, and never check the parameter list. The chunk of code above could just become

    def update(self, dt=0, recursive=True):
        if self.updating_suspended:
            return self
        for updater in self.updaters:
            updater(self, dt)

No parameter fetching necessary.

Incidentally, the current version forces each updater function to name its second parameter dt, if it has one. With my proposal, updater functions' second argument may be called whatever the user wants. If an updater function doesn't need to use the second argument, they can just ignore it.

Example

Here's a scene.

from manim import Scene, Integer, VGroup, Transform

def dummy_updater(obj, dt):
    return [i**2 for i in range(100)]

class TestScene(Scene):
    def construct(self):
        number = Integer(0)
        for _ in range(1000):
            number.add_updater(dummy_updater)

        self.add(number)
        for i in range(10):
            self.play(Transform(number, Integer(i)))

When executed with the current master, I get

$ rm -r media/
$ time manim -l scene.py 
...suppressed manim output...
real	1m7.297s
user	0m57.463s
sys	0m2.940s

When ran with my suggestion:

$ rm -r media/
$ time manim -l scene.py 
...suppressed manim output...
real	0m43.912s
user	0m40.581s
sys	0m2.781s

[kolibril13]

Nice!
This will save quite some time, and I don't see any big disadvantages.
Probably we should then also discuss, how updaters are supposed to be used.
I think especially when they are used together with Valuetrackers, we can have think of how they are used together, and if there is any way to make this more convenient.

Example 1 with Valuetracker:

class TestXX(Scene):
    def construct(self):
        dot_disp = Dot().set_color(RED)
        self.add(dot_disp)

        tick_start = 1
        tick_end = 2
        val_tracker = ValueTracker(tick_start)

        def my_updater(mob):
            mob.set_y(val_tracker.get_value())

        dot_disp.add_updater(my_updater)
        self.play(val_tracker.set_value, tick_end, rate_func=linear)
        self.wait()

And example 2, where the value tracker becomes an attribute of dot

class TestXX(Scene):
    def construct(self):
        dot_disp = Dot().set_color(RED)
        self.add(dot_disp)

        tick_start = 1
        tick_end = 2
        dot_disp.val_tracker = ValueTracker(tick_start)

        def my_updater(mob):
            mob.set_y(mob.val_tracker.get_value())

        dot_disp.add_updater(my_updater)
        self.play(dot_disp.val_tracker.set_value, tick_end, rate_func=linear)
        self.wait()

[leotrs]

Let me check if I understood correctly: you are suggesting that updaters become attributes of their parent mobject, for convenience. Correct?

[kolibril13]

updaters become attributes of their parent mobject, for convenience

No.
Valuetrackers become attributes of their parent mobject.

But this is only an idea that I use from time to time.
I think example 2 is a little prettier than example 1, however, I see potential that we could come up with something new, that would make this even nicer.

[leotrs]

Oooooh ok yes got it. Maybe we can discuss that in a separate issue ;)