Complex UI

Building and Animating Aomplex UI with Flutter

Updated: 23 December 2025

Notes from this talk by Marcin Szalek

Building Blocks of Complex UI

Look at some examples on Marcin’s Website

To build complex UI there are 3 core classes in Flutter

1. Stack/Overlay allows us to position widgtes in an absolute manner relative to one another, enabling things like overlaying
2. Transform is how we can apply transformations to widgets and control how it is painted. Rotations, positioning, etc. Transform.translate, transform.Rotate, Transform.scale as well as the default form which accepts a matrix for the transformation. Transforms happen before paint but after layout calculations are done
3. AnimationBuilder allows you to create interpolations between different widget states with which we use a Duration and AnimationController. The AnimationBuilder is called every time the controller’s value changes

How to Approach a Complex Design

1. Look it it’s already been implemented by an existing standard Flutter Widget or on the Flutter Widget of the Week
2. Identify static elements, something that we can replace with a single widget/block so we can think about what’s happening with the overall layout
3. Think about how the different elements are transforming
4. Wrap the overall AnimatedBuilder in a GestureDetector so we can use gestures to also control the process on our animation and then different handlers for setting the positions based on the motion