Render SGR 1 as bold when used with ITU colors

[j4james]

Summary of the Pull Request

The SGR 1 VT attribute can either be interpreted as a brighter color,
or as a bolder font, depending on the Intense text style setting.
However, the concept of brightness only applies to the eight standard
ANSI colors, so when SGR 1 is configured as bright, it has no effect
on the ITU T.416 colors (RGB and the 256 index colors).

To address that, we now interpret SGR 1 as a bolder font when applied
to ITU colors, regardless of whether the Intense text style option is
set to bold or not.

Note that this only applies to the Atlas render engine, since the GDI
engine doesn't support bold fonts.

Validation Steps Performed

I've manually tested SGR 1 applied to different color formats with the
Intense text style option set to None, and confirmed that the text
is now rendered with a bold font for ITU colors, but not for ANSI/AIX
colors.

PR Checklist

• Closes Use Bold To Mean Bold Text Where It Is Currently Ignored #18284

[DHowett]

Using the architecture you built yourself, you make this look easy.

Thanks for doing this. I know bold/intense/the true definition of SGR 1 is contentious, so let's see how this one goes over. 🙂

[DHowett]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[j4james]

Yeah, I don't think this is likely to be a problem, because it doesn't have the history of ambiguity that SGR 1 with ANSI colors had, but if anyone does complain, we can always add another option for it later.

I did consider maybe using the existing None option to disable it, but it's possible someone still wants bright with ANSI colors, but no bold on ITU colors, so that would require a completely separate toggle. So for now I figured it was best to keep it simple and see what happens.

[ianisl]

Hi, just found this update. This makes text appear bold in unexpected places, for instance in Vim when using fzf:

I don't like the effect. Is there a way to disable the new setting?

[lhecker]

But why would vim use SGR 1 with an ITU color in the first place? Brightening an ITU color doesn't make much sense to me... Shouldn't this perhaps get fixed in vim / your vim plugin?

[ianisl]

It's apparently an issue in Vim's built-in terminal which is used by fzf.
I admit it's a bit above my understanding of terminal colors but here's what seems a relevant (old) issue: vim/vim#5929
I don't think this will get fixed on Vim's side.

[ianisl]

Posting this since this could help others: I found a temporary workaround by disabling the emission of the SGR 1 attribute by Vim, using let &t_md = "".
It's not ideal but it does the job for now.