Warn users if the terminal font is not monospace

[Tyriar]

As a workaround for #35681, we could measure characters, maybe i and w and tell the user to use a monospace font if they differ.

[RubenMateus]

@Tyriar I would really like to help on this one has my first issue on vscode repo.

[Tyriar]

@RubenMateus that would be great!

To give you some pointers, there is an element used for measuring characters here:

https://github.com/Microsoft/vscode/blob/05b995dd9c99b709f41577ab04fe53740f67ccea/src/vs/workbench/parts/terminal/electron-browser/terminalConfigHelper.ts#L31

I see this as a new function on TerminalConfigHelper similar to _measureFont which checks the 2 characters and verifies they're the same width. This can be called by TerminalPanel when the font changes and show a notification (by adding INotificationService to constructor) if it's different:

https://github.com/Microsoft/vscode/blob/05b995dd9c99b709f41577ab04fe53740f67ccea/src/vs/workbench/parts/terminal/electron-browser/terminalPanel.ts#L78-L82

[jay-khatri]

@Tyriar have there been any developments on this issue? I'd love to take a look!

[Tyriar]

@jay-khatri not yet, go for it 😃

[jay-khatri]

@Tyriar I took a look and wanted to clarify. I understand that the point of this is to confirm whether or not a font is monospace. With that being said, am I expected to render an actual html element and measure the difference among two separate letters (eg. in pixels)? I'm now pretty familiar with the code organization, just a little confused as to how to approach measuring the font 🙂

[jay-khatri]

Ping @Tyriar 😬 🙂

[Tyriar]

@jay-khatri yes, by utilizing _charMeasureElement which I believe has font assigned to it

[Tyriar]

#48028 adds the following notification when the terminal font is changed:

[roblourens]

Works, but I don't see the notification if I have the terminal closed, then change the font setting, then open the terminal. I think it should be shown in that case too.

[Tyriar]

@rebornix any ideas on whether the editor has something to leverage here? Basically I need some element to measure the width of w and i to check if it's really a monospace font but it only works when the panel is visible. I don't really want to break out of the panel element and touch things that the terminal doesn't own.

[Tyriar]

I'm toying with the idea of supporting this in xterm.js by specifying a measureContainer element to do the measurements in xtermjs/xterm.js#702. That would move the logic upstream, it would still be a little weird for me to put this element somewhere outside of the terminal panel though.

Ping @rebornix

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