html: Add Unicode 11 xterm.js addon

[mikelorant]

Add Unicode 11 addon to xterm.js to enable support for newer Unicode standards. This addon significantly improves rendering of emojis.

[mikelorant]

@tsl0922 Will need some advice on how I activated the feature. Not sure I activated it in the preferred location. Feel free to recommend any changes or improvements.

For reference this is the line I am uncertain about:

terminal.unicode.activeVersion = '11';

[tsl0922]

For reference this is the line I am uncertain about:

terminal.unicode.activeVersion = '11';

Maybe it can be a Client Option, if we want to extend it to support unicode-graphemes addon later.

[mikelorant]

I think once the unicode-graphemes addon becomes stable it would be worth switching over.

The reason I didn't make Unicode 11 an option was I can't think of why you wouldn't want this always enabled. What benefit do we gain from this being an option? Without this being set, most emoji are just rendered incorrectly.

[tsl0922]

What benefit do we gain from this being an option?

You can enable / disable this addon, or switch to unicode-graphemes later.

[mikelorant]

You can enable / disable this addon, or switch to unicode-graphemes later.

Does this mean we want something that has a value of unicode-11 or unicode-graphemes so you select which support you want?

[mikelorant]

You actually have me thinking, should we add unicode-graphemes and mark it experimental, while setting the default to unicode11. Can do all the work now and later on just switch the default.

[tsl0922]

Does this mean we want something that has a value of unicode-11 or unicode-graphemes so you select which support you want?

The value should be valid for term.unicode.activeVersion, for example: 11 / 15-graphemes (6 if both disabled)

Ref: https://github.com/xtermjs/xterm.js/blob/1da0db435f93879a60b9badbb663852ff3223063/demo/client.ts#L659-L679

should we add unicode-graphemes and mark it experimental

No, unicode-graphemes is not published to npm yet.

[mikelorant]

So let me clarify this before I get started:

1. We add a new client side variable: unicodeVersion.
2. If unset default is 11.
3. Can also be set to 6 or 15-graphemes.
4. If set to 11 we enable the unicode11 addon.
5. If set to 15-graphemes we fallback to default 11 and enable unicode11 addon.
6. If set to 6 we do nothing (not enable the unicode11 addon).

This is slightly different to your earlier post but I think it makes more sense to have Unicode 11 as the default. Unicode 6 is just way too old and renders very differently.

Happy to adjust this logic though based on your feedback.

[tsl0922]

1. We add a new client side variable: unicodeVersion.
2. If unset or unknown value, use the default 11.
3. If set to 6 we do nothing (not enable any unicode addon).

We don't need to handle values for unicode-graphemes before it is included in ttyd.

[mikelorant]

Thanks for merging this! 🤞 when this is released there are no issues.