Xterm.js: Support fast scrolling using a modifier key

[Tyriar]

Downstream: https://github.com/microsoft/vscode/issues/78431

VS Code has a setting editor.fastScrollSensitivity which multiplies the scroll speed when a particular modifier is down. This should be pretty easy to implement, we need to think about how the API should look. We probably need a number for the multiplier and an enum for which modifier (see https://github.com/microsoft/vscode/pull/78555).

[Tyriar]

Proposal:

fastScrollSensitivity: number
// undefined = disabled, default alt?
fastScrollModifier: 'alt' | 'ctrl' | 'shift' | undefined

[csurquin]

Hello,

I am looking for a good first issue to get started in open source projects and this one seems doable. May I try to tackle this? Do you have any hint about where to start?

Thank you!

[Tyriar]

@csurquin sure, this is a good one as it's pretty well defined. You should be able to find all the places you need to add a setting for by following one of the existing settings, eg.

https://github.com/xtermjs/xterm.js/blob/a89771a8de58fbc7a82323fb7d6d9c421ef63535/src/common/services/OptionsService.ts#L25

I think these are only the places where the scroll would need to be multiplied:

https://github.com/xtermjs/xterm.js/blob/a89771a8de58fbc7a82323fb7d6d9c421ef63535/src/browser/Viewport.ts#L171-L209

[csurquin]

I made a pull request for this feature. I hope I did it the right way.

[Tyriar]

Fixed in https://github.com/xtermjs/xterm.js/pull/2375