Re: "Fix" sag scaling for hidpi

[Lars Ingebrigtsen]

Alan Third <alan@idiocy.org> writes:

> Ah, I've misunderstood how GTK deals with scaling. I could've sworn
> someone said upthread that SVG images are shown at double size, the
> same as on macOS, but apparently not.

I tried loading the splash.svg file, and it's displayed here the same
size as the splash.png file.  Debian bullseye, HiDPI, scaling factor of
2.3, so the 333-pixel-wide image is displayed as a 760-pixel-wide image:

(insert-image (create-image "~/src/emacs/trunk/etc/images/splash.png"))
(insert-image (create-image "~/src/emacs/trunk/etc/images/splash.svg"))

> So we have the situation where on macOS everything is shown at logical
> size, unless you specifically ask for it not to be, and on GTK
> everything is shown at physical size, unless you ask for it not to be.
>
> And they both use "scale factor" for these same things.
>
> What does the PGTK port do? The same as XGTK?

This is a Gtk Emacs, but not a pgkt Emacs -- I haven't tried the pgtk
branch...

> Nope, it's the same as on macOS.
>
> So on macOS and PGTK we want to use the scale factor to scale down
> images so they are displayed with physical pixels, and on XGTK we want
> to scale up (UI?) images so they are displayed in logical pixels.
>
> I'm somewhat inclined to ignore XGTKs desires, especially as it seems
> it may be removed once PGTK is merged.

It sounds like confusion born out of some architectures reporting sizes
as logical pixels, and some as physical pixels.  That has to be fixed,
or we'll just confuse ourselves even more.  :-)

>> Uhm...  but on Macos, Emacs doesn't know the physical pixel size, I
>> think you said earlier?  So...  er...  now I'm confused.  :-)
>
> It's something you have to go looking for specifically, usually
> through multiplying by the scale factor. The reason I said I wouldn't
> want Emacs to convert everything to physical pixels is because every
> single size would have to be multiplied or divided by the scale
> factor, and then Emacs would appear to be half the size of every other
> app (font sizes would be half what they are in the terminal, for
> example).

I don't follow.  This Gtk Emacs is exactly the size I want it to be, and
it computes everything in physical pixels.

If the OS expects logical pixels, then we scale before asking the OS to
do something -- this is how Gtk menus are computed, for instance.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no