Dart: Get bytes from Flutter-Canvas without opening Flutter App

Background

I am developing a pure Dart command line tool, which combines images from files.

Think creating NFTs by stacking images.

Using the pure Dart image library is slow, it takes about 11-20 seconds for one image sized 3000 x 3000.

Tried

Adding Flutter and using Flutter-Canvas to increase performance does not allow me to compile a Dart command line EXE.

I tried flutter build windows but the result always does open a window / head. And it does not work, just sits there.

Questions regarding possible solutions

Is there a way to combine images more efficently than image?
Is there a way to create a Dart command line EXE which uses Flutter-Canvas as a library?
Flutter Tests run headless; is there a way to imitate that behaviour und thus run Flutter-Canvas headless?

Solution

Flutter Tests

One approach would be to hijack Flutter Tests, but these cannot be turned into a redistributable app or command:

Command Line Package

A different apporach would be to use this package, which modifies code in the ./windows folder:

This plugin allows you to run a flutter windows app in gui, or commandline mode. io.dart is used to access stdout and stderr