This is not a fix, only an extra-ugly workaround so that at the very
least we don't end up with a splash screen taking the whole display on
Wayland.
Basically by setting 1/3 as the max splash size, a Wayland desktop with
no scale ratio will have a splash taking a third of the screen while it
would take 2/3 of the screen with a scale ratio of ×2 (of course, it
will still be very broken with a scale ratio of ×3 but are there
displays needing such high scaling?). The real fix will be when GTK/GDK
fix their API so that it returns what the docs says it should (i.e. a
size in "application pixels" not "device pixels"), as it does on X11,
Windows, macOS… Then we won't create random max size and we will be able
to properly control our splash size.
Note that this neither fixes nor works around the position issue on
Wayland (in my case, the splash was just always on top-left of the
display).
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