bug#42304: 27.0.50; Emacs does not adjust to global font scaling anymore

[Po Lu]

Torsten Bronger <bronger@physik.rwth-aachen.de> writes:

> This still is an issue, also on Wayland and pgtk.  The commit
> f208d5ae77 that introduced the problem is long but since
> --without-harfbuzz does not change anything, much of the commit diff
> can be ignored, I suspect.
>
> @Po Lu: Since you seem to be into the low-level display code
> currently, I shamelessly Cc’ed you.  Of course, this is not a
> demand but possibly you have an idea.

I don't understand how that could ever have worked, since there was
never any code to handle the GNOME text scaling factor outside the PGTK
port.

In the PGTK port, that factor is only applied on startup by the toolkit
itself.  We don't have any code to recreate fonts and cairo surfaces
when it changes.

So it would be helpful to see exactly what caused Emacs to dynamically
adjust the default font size before Harfbuzz shaping was introduced, and
why it doesn't work afterwards.