rich.style support for large type using mosaic or line-drawing

[rbanffy]

Larger type using block or line drawing characters can provide some richer UI experiences and help make elements stand out. Unicode provides both a full set of line drawing characters and 2x2 and 2x3 mosaics (as well as a wide assortment of other semigraphic blocks) and even 7-segment digits that fit in a character cell. Some terminal programs (all VTE and QtTermWidget ones) render those symbols even if no font in the system defines them.

These tricks are used to great effect by programs such as htop (https://github.com/htop-dev/htop/blob/39db3eb6f7a5d892d6343d5b3d574cf34ab150ee/Meter.c#L367-L371) and libraries like urwid (https://github.com/urwid/urwid/blob/bd573439ab5776c3511d7b82d98d00a50c9e1273/urwid/font.py#L190-L451). Some terminals (Apple's Terminal and xterm) can also support DEC's old double width and height (which are line-based and not cell-based attributes).

There are some complications however - these larger composite glyphs are more than one cell high and 2 or more cells wide. Does anyone (besides me) want this feature?

[willmcgugan]

I've used pyfiglet for this kind of thing, which was fairly easy to integrate with Rich and also Textual (https://github.com/willmcgugan/textual/blob/main/imgs/textual.png).

I'm not sure if this belongs in Rich itself, as I don't think there will be that many people who want to use it. But it could be an external package. I could make an exception for those htop digits which loop temptingly easy to integrate.

I've noticed the double sized characters in the spec, but left them out since they aren't well supported. I am tempted, but I'm not keen to have to design graceful fallbacks for them.

I could still be persuaded. Let's see what others think. I'm especially interested in an apps which do this kind of thing well.

[honno]

+1 just the htop digits.

Note the block characters seem to render quite consistently on terminal emulators, but otherwise they render super inconsistently across software and websites.

[rbanffy]

The problem with pyfiglet is that the figlet font format is not easy to create fonts for. 2x2 blocks render very consistently. 2x3, being part of a recent Unicode standard, require font support on some platforms (although most sensible Linux terminal emulators are covered). The next edition will again add a new set of mosaics, originally from Kaypro computers (the 3x3 were from Teletext and TRS-80 systems), that's 2x4. I'm assuming this will be the last batch of mosaics for quite some time (they were added for interoperability with old platforms).

If you opt to support multi-line glyphs for the htop-like digits, adding multi-line glyphs such as the ones I mentioned from urwid can follow the same logic. The textual calculator example would be an interesting application for that - both 7-segment-like and nicer mosaic-based ones.

You are right about the double width and height - there is no plausible fallback except removing the escape sequence (as tmux does) and, since just about every terminal lies about being xterm, which supports this feature, the situation is even worse. I use double width but only for streaming character output and error messages because, in terminals that don't support it, it becomes just another line with default width characters.