When to use AnimatedWidget vs. AnimatedBuilder.

This tutorial shows you how to build explicit animations in Flutter.
After introducing some of the essential concepts, classes,
and methods in the animation library, it walks you through 5
animation examples. The examples build on each other,
introducing you to different aspects of the animation library.

The Flutter SDK also provides built-in explicit animations,
such as FadeTransition, SizeTransition,
and SlideTransition. These simple animations are
triggered by setting a beginning and ending point.
They are simpler to implement
than custom explicit animations, which are described here.

Essential animation concepts and classes

What's the point?

Animation, a core class in Flutter’s animation library,
interpolates the values used to guide an animation.