New backend - Textual

[freakboy3742]

What is the problem or limitation you are having?

While graphical APIs like Cocoa and GTK are the default for modern laptops, sometimes a console based interface is useful.

Describe the solution you'd like

We should add a backend based on Textual. This would allow a user to take their Toga app, and deploy it as a console based app.

Describe alternatives you've considered

Curses would also be a possibility for a console backend; however Textual has a much richer widget API, and is known to have integration with Python's asyncio libraries.

Additional context

• Some APIs will likely be no-ops - for example, fonts and window size changing APIs will likely be impossible.
• Some widgets won't be possible - Canvas and ImageView are definitely impossible; WebView would be... an interesting challenge.
• Some sort of scaling factor between pixels and characters will be needed. Assuming an 80x24 console is the same as an 800x600 screen might be a good starting point for this sort of calculation.
• Changes to Briefcase may be needed to allow for command line apps (see Generating a command-line executable without the GUI features briefcase#556)

[brendan-simon-indt]

Not sure if this is relevant or not, but some apps can start as a GUI or console, typically be passing explicit arguments on the CLI (or inferred from arguments). e.g. a batch mode where files are supplied as arguments. No files specified => GUI displayed to browse for files or some dashboard with action buttons, etc.

[freakboy3742]

@brendan-simon-indt Thanks - but that's really a UX decision for an individual app to make. This ticket is about providing a different option for building that GUI - a text mode "GUI" (something that could be run over a TTY session), rather than a traditional windows/macOS/Linux "GUI".