This repo contains various apps that range from extremely simple all the way to a simple 3D viewer.
This app is a functional Brensenham triangle rasterizer based on Leen Ammeraal's book. It also incorporates the Top-Left rule.
Also: Full res Video
Installing Dart separately yields something different. You really should upgrade Dart via Flutter:
This issue is because of the dart version and by updating flutter the dart version won't update, the way for solving this is, first, you need to be on the dev or master channel,
flutter channel master
flutter upgradeafter that run flutter doctor -v as you see your dart is still an old one
in this step, you should update it manually, as the doc says Dart
dart create ttf_example