bug#48307: Feature request: provide default keybindings to change the font size in all windows

["Clément Pit-Claudel" <cpitclaudel@gmail.com>]

On 5/9/21 4:23 AM, Eli Zaretskii wrote:
> So: what should be the effect of this "global" change of the "font
> size"?  Some thought-provoking questions:

Thanks.  Some wild guesses:

>  . should this affect only the faces whose fonts don't define their
>    own size, or should it affect _all_ fonts?

Probably all of them except the ones that specify an absolute height?

>  . should this really affect _all_ the buffers? e.g., what about the
>    minibuffer and the echo-area buffers?

Yes, certainly.

>  . should this affect all the frames or just the currently selected
>    frame? what about future frames?

I'm guessing all frames.

>  . should this affect the mode line?

Absolutely.

>  . should this affect tooltips?

Yes, to the extent that we have control over that.

>  . should this affect the fringes and their bitmaps?

That would be nice.

>  . should this affect the menu bar, the drop-down menus, and the GUI
>    dialogs?

That's extra credit; I guess it could be nice?

> We need a clear understanding of the feature before we implement it,
> IMO.

Indeed, although starting with an implementation and refining it over time could be good, too (to some extent I think the specifics matter less than having something available).  For example, just including any one of the short implementations into Emacs by default would work to solve the concrete issue that I'm talking about (with the pandemic we do screen-sharing all the time, and I hear "how do I resize the font in Emacs again?" more than once a week these days ^^).

A good approximation of what I would like that command to do is what menu-set-font does if you ignore the part about changing the face and only change the size part.  Something similar to doing text-scale-adjust in every buffer would also work, too (I've noticed that changing the :height attribute of the default face is slow, while text-scale-adjust is fast).