Extremely slow to load json

[JCKodel]

I was using https://pub.dev/packages/lottie to render Lottie animations, but it doesn't render animations very well (for instance: xvrh/lottie-flutter#323).

So, I used this library, which renders that animation correctly, but, it is extremely slow to load a json (generated by https://pub.dev/packages/dart_animated_emoji).

It is so slow that navigation animation freezes completely (almost 1 second of stuttering while changing the json or navigating to a page where the viewer is on).

[blaugold]

Thanks for raising this issue, and sorry for the late response!

When using a LottieView, the native LottieAnimation is created on the UI thread. If I understand it correctly, dart_animated_emoji ships one big Lottie file. Decoding that into a LottieAnimation is probably taking quite a bit of time and is blocking the UI thread.

Maybe we can offload that to another thread. But we should also allow users to preload animations and only insert the LottieView into the UI tree once the Lottie animation has been loaded. Otherwise, the Lottie animation would pop in at some point (in your case ~1 second) which would still be a pretty bad UX.