Run the app and look for images rendered with a randomly colored
checkerboard, indicating that the image is cached.
As you interact with the scene, the checkerboarded images
should remain constant—you don’t want to see flickering,
which would indicate that the cached image is being re-cached.

In most cases, you want to see checkerboards on static images,
but not on non-static images.  If a static image isn’t cached,
you can cache it by placing it into a RepaintBoundary
widget. Though the engine might still ignore a repaint
boundary if it thinks the image isn’t complex enough.

Viewing the widget rebuild profiler

The Flutter framework is designed to make it hard to create
applications that are not 60fps and smooth. Often, if you have jank,
it’s because there is a simple bug causing more of the UI to be
rebuilt each frame than required. The Widget rebuild profiler
helps you debug and fix performance problems due to these sorts
of bugs.