Custom Animation Class

[AhmedMajedKaz]

I have two question, Can you please answer it if you know. First: I search in "https://github.com/3b1b/videos" and found some classes that are inherited from Animation and Transform Class, my question is how to make my custom animation class ?, I don't think this is mentioned in the documentation of Manim. Second: how transform animation work? I search in Transform Class, but I don't understand how it work because I learn python recently, And I want to know how transform and interpolate between two shapes happens. and thanks.

[sahilmakhijani]

class RotationAnimation(Animation):
    def __init__(self, mobject, angle, **kwargs):
        self.angle = angle
        super().__init__(mobject, **kwargs)
    
    def interpolate_mobject(self, alpha):
        self.mobject.set_points(self.starting_mobject.get_points())
        self.mobject.rotate(alpha * self.angle)

class RotationScene(Scene):
    def construct(self):
        self.play(
            RotationAnimation(Square(), 45 * DEGREES),
            rate_func=linear,
            run_time=1
        )

Check this example for Custom Animation.

While defining custom animation, you should know what alpha is. Alpha ranges from 0 to 1 throughout the animation. For rotation, Now, when animation starts I want object to be 0 degrees tilted from starting object and at the end it should be 45 degrees tilted. So, if I tilt alpha * 45 Degrees, then it should work properly.

If the frame rate is 60 and runtime is 1 second, so interpolate_mobject will be called 60 time per second. At first alpha will be 0, so 0 degress tilt. After half second, alpha will be 0.5, so you will tilt 22.5 degrees. At last alpha will be 1, so you will tilt 45 degrees. That's why it would be a smooth animation from 0 degrees to 45 degrees tilt.

[WampyCakes]

I really like this example, but I think you may be right. It's best if we can avoid creating our own mobject for the example and instead we focus on creating a custom animation class. I think that covers 1 and 2.
3. Considering it may be a bit too much of an explanation and need changed, no.
4. I don't know exactly what the problem is anyhow 😅

Regarding any copyediting, we'll take care of that in the PR. So once you have a legible example, we can fine tune the wording of it :) Thanks for your work thus far!

I think the introduction looks good btw

[sahilmakhijani]

I can't think of an example where there is no custom Mobject and it also justifies the need of custom animation. So, should I just add the rotation example that I've answered on this thread? Any other ideas for custom animation examples?

[sahilmakhijani]

Rotate is manim's inbuilt animation, that's why I changed the example for docs

[sahilmakhijani]

I guess this thred is not the best place to discuss this. Should I open a seperate issue or draft pr for this?

[WampyCakes]

I don't think it needs to be justified. You can use the example of something already built into manim, like rotate, to explain how it works so that when someone has their own thing they want to animate, they can see how to do it. They'll already have their own justification at that point. That's all this example really needs to convey I think.

A draft PR works

[sahilmakhijani]

For the second question, transform animation works by calling interpolate on the corresponding type of Mobject, which can be VMobject, ImageMobject, etc. Interpolate method of each type of mobject takes care of how to interpolate between two mobjects and gives a transforming effect.