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Physics-Based Animations with Flutter's AnimatedBuilder


Hello, Flutter enthusiasts! Today, we're going to explore a fascinating aspect of the Flutter universe: Physics-Based Animations using AnimatedBuilder. Sounds like a lot of fun, right? Well, prepare to be amazed as we set off on this journey that's all about movement, physics, and some magic dust from the world of Flutter.

But first, we need to answer the question: why physics-based animations?

Why Physics-Based Animations?

By using physics-based animations, we can emulate real-world motion in our apps. This approach lends a more natural feel to your animations, making them look smooth and responsive. Flutter gives a thumbs up to this idea with its physics simulation package. Using the flutter/physics package, one can create animations that feel incredibly real and intuitive.

Alrighty then, now that we know why we're here, let's dive into the how.

Flutter and AnimatedBuilder

AnimatedBuilder is a widget that rebuilds when the Flutter framework calls the build method which, in turn, calls the builder callback. This callback is usually triggered by an animation notification.

A simple example of an AnimatedBuilder is like this:

  animation: _animation,
  builder: (context, child) => Transform.rotate(
    angle: _animation.value,
    child: FlutterLogo(size: 200),

In this snippet, the Flutter logo rotates according to the value of _animation.

Introducing Physics

Before we combine AnimatedBuilder and physics-based animations, let's get familiar with the physics package in Flutter.

final spring = SpringDescription(
  mass: 1,
  stiffness: 1,
  damping: 1,

In the example above, SpringDescription takes three parameters: mass, stiffness, and damping, which are basic physical properties of a spring system that can be tweaked to get the desired animation effect.

Physics Meets AnimatedBuilder

With our newfound knowledge of SpringDescription, let's integrate physics-based animations with AnimatedBuilder.

Imagine we're creating a bouncing ball animation. The ball should bounce in a realistic manner, mimicking the movement of a real-world bouncing ball. We'll use the flutter/physics package for this.

First, we need to define our animation controller:

late final AnimationController _controller = AnimationController(
  vsync: this,
  lowerBound: double.negativeInfinity,
  upperBound: double.infinity,

Next, we will need to define our spring physics:

final spring = SpringDescription(
  mass: 1,
  stiffness: 100,
  damping: 10,

Now, let's add the simulation:

_simulation = SpringSimulation(spring, 0, 1, -1);

In the line above, SpringSimulation takes four parameters: the spring description, start position, end position, and velocity.

Finally, let's add our AnimatedBuilder:

  animation: _controller,
  builder: (context, child) {
    return Transform.translate(
      offset: Offset(0, (_controller.value - 0.5) * 200),
      child: child,
  child: FlutterLogo(size: 200),

The Transform.translate provides a translation transformation, which essentially moves the child by an offset.

Voilà! You have your physics-based animation, all set and ready to bounce.

Wrapping Up

This was just a quick dive into the exciting world of Flutter's physics-based animations using AnimatedBuilder. There is so much more you can do! The sky (or rather, the logic of your physics simulation) is the limit.

Remember, the key to masterful animation is experimentation. Play around with the values, mix different physics simulations - the aim is to make your app feel more lifelike and responsive. The world of Flutter physics-based animations is vast and mostly unexplored, so get creative!

Happy Coding!