A soft reset (DECSTR) should not be erasing soft fonts

[j4james]

Windows Terminal version

1.25.1322.0

Windows build number

10.0.19045.6332

Other Software

No response

Steps to reproduce

1. Download one of the example fonts from here: https://vt100.net/dec/vt320/fonts
2. They use 8-bit escape sequences so you'll need to enable 8-bit mode first with something like echo -e '\033%@' in a WSL shell.
3. Then cat the fnt file to download it to the terminal. All subsequent text will immediately begin using that font.
4. Perform a soft reset with echo -e '\033[!p'.

Expected Behavior

After the soft reset, the custom font should still be active.

Quoting the DECDLD notes from DEC STD 070-10, on page 6:

A Soft Reset function (DECSTR) does not erase font files loaded by the DECDLD command

Actual Behavior

The font gets reset to the original terminal font.

[j4james]

The problem is caused by the TerminalOutput::SoftReset method here:

terminal/src/terminal/adapter/terminalOutput.cpp

Lines 34 to 39 in 2058813

	void TerminalOutput::SoftReset() noexcept
	{
	// For a soft reset we want to reinitialize the character set designations,
	// but retain the GR translation functionality if it's currently enabled.
	*this = { _grTranslationEnabled };
	}

That basically regenerates a fresh instance of TerminalOutput, which loses the DRCS state in the process. In addition to the _grTranslationEnabled field, we also should be preserving the _drcsId and _drcsTranslationTable fields. And if the DRCS set has replaced either the ASCII or UPSS sets (which is the case in the example above), it'll also need to be reassigned as the default GL or GR mapping.

I'll try and create a proper PR for this oncee I've had a chance to test it some more, but here's a patch I created which I think should fix the issue: fix-soft-font-reset.patch

[DHowett]

oh wow, I suspect we were a bit overzealous when we tried to make resets cleaner. Good catch!

[DHowett]

(fwiw, patch looks good - would be happy if you sent in a PR even if you then had to iterate on it :))