Add a Scroll Animation

[icedcoffeeee]

Description of proposed feature

I find myself creating this new class for my projects, and thought if it might be useful for other users.

class Scroll(AnimationGroup):
    def __init__(self, mob, target_mob, shift=UP):
        super().__init__(
            FadeIn(target_mob, shift=shift),
            FadeOut(mob, shift=shift),
        )

How can the new feature be used?

class Test(Scene):
    def construct(self):
        a = Text("Hello")
        b = Text("World")
        self.add(a)
        # self.play(FadeIn(b, shift=UP), FadeOut(a, shift=UP))
        self.play(Scroll(a, b))
        self.wait()

Output:

Test.mp4

Additional comments

I'm just not sure if this might be too simple of an addition for manim

[WampyCakes]

This looks like one of those things that belongs as a Transform. IIRC we have a lot of different Transforms that should be consolidated like Fades were.

[Darylgolden]

I would love this!

[behackl]

We do have a FadeTransform; maybe this could be implemented via a shift parameter for it?

In general, FadeTransform tries to be a bit clever: the default behavior is to have the submobjects of the starting mobject move towards the submobjects of the target mobject, so you will notice that FadeTransform(a, b) in your example will cause the letters to look as if they are moving.

Semantically, "different" behavior for specifying a shift still makes sense IMO: If None is passed (the default), the submobjects try to determine their shift target individually, whereas when shift is specified, both original and target mobject are shifted by the specified amount.

I think this would be a nice addition to FadeTransform.