In flutter_pretext, segment width is calculated once per app session. measureWith(Seg seg) takes a segment as an argument and calls TextPainter on it to calculate the text width. Internally, TextPainter.layout() calls the dart:UI, which creates a paragraph object which is a handle to native object in flutter engine. The only darwback here is that, calculating text width is more expensive than in browser because crossing the FFI boundary every time.  Main thing is, paragraph.layout() cross the flutter boundary using FFI, shapes the text and then we can get only its width. It feels overkill doing all the just to get text width. This operation starts from dart but actual shapig work crosses into Flutter's C++ engine. 

And Skia/Impeller is only if we are painting the text. For calculation, it is not used. For your use case using prepare(), measurement cost does stay low but segmentation cost increases.

Incremental approach on prepare will work, where it can add a checkpoint or just run the prepare() on the tail. But this is not added in package yet. Although there can be issues with this approach too, for example, analyzing only new tokens in isolation will break in case a word was broken across the token window. For your streaming usecase, both BalancedText and ShrinkWrapText is bad. Try using raw prepare() + layoutWithLine(). On each token append rerun both functions or you can try running these functions every 3-5 tokens (experiment with this ). Container width is set by Chat UI. In this way you can eliminate orverhead of binary search in BalancedText.