Investigate alternative ways to handle box drawing/block elements

[DHowett-MSFT]

There've been some concerns about how we scale glyphs in the Box Drawing character block.

Other terminal emulators do interesting things:

• Gnome-terminal uses little 5x5 bitmaps and stretches them to fill the entire cell (shout-out to @egmontkob for telling me this!)
  • This results in pixel perfect lines and shading.
• [Other popular terminal] uses line-drawing primitives at the graphics layer to mimic box drawing and rect-filling primitives with opacity to mimic block elements
  • This also results in pixel-perfect lines and cool blended shading glyphs.

We chose not to do these things for v1.0 because we learned that certain fonts (monofur is a good one) have their own unique styles for box drawing and block elements that we wanted to preserve.

Proposed solution

• Add a setting for "Let Windows Terminal handle block / powerline drawing"
  • This is a per-profile setting. profile::compatibility.builtinBlockDrawing
  • When enabled, Terminal will manually draw box-drawing and powerline glyphs, replacing the glyph from the font
  • Enable this by default
    • Obviously, users will be able to opt out
    • This will give us the benefit of getting PL glyphs even for fonts without them!
  • We should probably start with a few of the glyphs as higher pri:
    
    • Green: Definitely, in v0
    • Yellow: okay probably yea
    • Orange: meh
    • red: probably too expensive (engineering wise)
    • white: I can't imagine we'll actually need to draw these
• Add a secondary setting for "Replace filled rectangles with transparent glyphs"
  • Only enable if compatibility.builtinBlockDrawing is enabled

Links

• Box drawing characters are not antialiased #6161 Block-drawing glyphs aren't antialiased
• Add preference to customize vertical line spacing #3498 may affect how we choose to draw these "pixel-perfect" glyphs.
• Anti-Aliasing for powerline font icons is poor when using 12 pt or lower #7260

[benc-uk]

The shaded/hatched boxes now look really bad since the last update.
A lot of themes like Powerlevel10k use these

This is my prompt now in Windows Terminal

This is what it should look like (In VS Code)

[DHowett-MSFT]

yikes.

[DHowett-MSFT]

Though, that looks like Cascadia Code. The version released yesterday with the new metrics works properly with Terminal. You may need to update.

[benc-uk]

Hi, I just updated to CascadiaCode_2004.30, and I didn't see any difference :(

Weirdly if I set my font size to 15, the shading disappears altogether, and at font size 19 it looks perfect, but that's just too huge to use!

[benc-uk]

Some further tests with Cascadia Code.

At font size 14 the line elements are super thin and the curved corner lacks any antialiasing/smoothing

At font size 13 they look much better

[mdtauk]

I think if this is added, it should be behind a setting. Something like

☑ Let Windows Terminal handle block character drawing

Cascadia code has an interesting approach to the character of some of it's Block Characters, and other fonts will also. That character is lost by Terminal doing it itself - so it should be optional IMO