Introduce scale_factor option

[BHatGuy]

What kind of change does this PR introduce?

• Feature

Did this PR introduce a breaking change?

A breaking change includes anything that breaks backwards compatibility either at compile or run time.

• No

I tried to implement the scaling proposed in #1301. I decided to use an additional factor to the os_scale_factor.

Example for using the new scale_factor with key bindings:

let g:neovide_scale_factor=1.0
function! ChangeScaleFactor(delta)
    let g:neovide_scale_factor = g:neovide_scale_factor * a:delta
endfunction
nnoremap <expr><C-=> ChangeScaleFactor(1.25)
nnoremap <expr><C--> ChangeScaleFactor(1/1.25)

[MultisampledNight]

This is great, thank you! I'll add the snippet to the FAQ.

[MultisampledNight]

(by the way, you might want to check out cargo fmt and g:rustfmt_autosave)

[TRPB]

Thanks for this @BHatGuy. I've noticed on 0.12.2 at least that I have to press another key after changing the scale factor, it's not instant. Is there any way we can trigger an instant change? It doesn't seem to matter what is key is pressed, even a mouse click works.

I wonder if there's some kind of refresh() function we can call to force it each execution?

[fredizzimo]

It should be instant in the latest 0.13.3 release, and some releases before that.

It was probably this one that fixed it:

• handle scale_factor change early #2610