Control: Attributed Label

[migueldeicaza]

To make it simpler to add a splash of color to the UI.

Some thoughts:

• Attributed strings should allow overlapping attributes
• Attributed strings should have an HTML-like input system for ease of creation.

Tags:

• <b> - bold
• <u> - underline
• <r> - reverse

Colors:

• <red>, <green>, <yellow> etc

[tig]

What about just supporting the ANSI Escape SGR parameters?

This way we don't have to invent new markup.

If we re-built Label on top of XTermSharp we'd get this mostly for free.

Related: #432 & #299

In my opinion we should do the following:

• Implement a robust read-only text engine that supports:
• left, right, center, justifiied justifiction
• line wrap (both word and character based)
• rendering ANSI color/formatting sequences
• Put this text engine under Label

Use Label as a child control (or renderer) inside all other controls that display read-only text: Window.Title, MessageBox, TextField, etc...

@migueldeicaza has been doing work on a better text editor component for SwiftTerm. I suspect that work will not be useful to Terminal.Gui since it's probably tied to iOS. I think having a robust read-only text engine is more important that having BOTH that and an editor. And I'm not convinced they need to be based on the same thing (although one could argue that you'd read-only to just be a read-only version of edit.

(FWIW, I recently built an engine that comes close to this as part of https://github.com/tig/winprint. It doesn't support right, center, or justified and has lame word wrapping, but it DOES do ANSI formatting. It is based on https://github.com/rasmus-toftdahl-olesen/libvt100. I didn't know about @migueldeicaza's XtermSharp when I started, and XtermSharp doesn't support > 8bit color sequences, so I kept with libvt100. It's possible that one way to build this all is to simply layer it on top of XtermSharp or libvt100. I may build a POC of this.)