[Development] Updated high-DPI support for Qt 5.14

[Elvis Stansvik]

Den ons 25 sep. 2019 kl 18:34 skrev Matthew Woehlke <mwoehlke.floss at gmail.com>:
>
> On 25/09/2019 08.54, Morten Sørvig wrote:
> > I see two differences between setting the DPI vs a factor:
> >
> > - You set one value per screen (DPI) instead of two (DPI & factor)
> >
> > - Qt can compute the factor, according to policy set by the application (as mentioned above)
> >
> > [...]
> >
> > If possible, I’d like us to move away from relying on setting
> > environment variables, and/or switch to specifying per-screen DPI
> > instead of a scale factor.
> Has anyone considered whether or not this is *user* friendly?
>
> As a user, I don't want to have to know/measure/compute the DPI of my
> display device. I just want to make "stuff" bigger or smaller. I *also*
> don't necessarily want the same physical size of "stuff" across devices.
> On my phone, I may want smaller "stuff", because my phone is usually
> quite close to my eyes. On my 4K 75" television, I may want larger
> "stuff" because I'm sitting 10' to 15' away. Maybe I have really good
> (or really bad) eyesight.
>
> Fiddling with "fake DPI" as a way of adjusting things has always felt
> like a hack. Setting display scaling "just makes sense". From a user
> perspective, it's obvious that scaling is also going to affect icons,
> style margins, frame thicknesses... basically, *everything*. DPI,
> historically, only affected font sizes and *maybe* some margins. If the
> only knob I have is DPI, how do I know (or control) what size my icons
> will be? How am I supposed to guess what will be the relation between
> "virtual" pixels and physical pixels, keeping in mind that I, as a user,
> am trying to achieve a particular value for that?
>
> There are a few instances, such as when representing physical objects,
> when it makes sense to try to achieve a particular physical size. In
> almost *every other case*, which is to say *always* for interface
> elements, there is no fixed correlation between "desirable" size and
> actual physical size, and anyone that designs their application
> otherwise is doing their users a disservice.

Agree 100%. There's no reason for a user to have to fiddle around with
a strange number like 192, 96, or whatever.

As a user I want 2 things:

- Sane defaults and good autodetection, so a hopefully good automatic
scale factor that makes things reasonably sized given the physical
dimensions of the output device and its intended viewing distance
- ..but if I want to tune the size for whatever reason, I want to do
that in percentages of what it is *now*.

It's easy enough for most folks to judge what % of the current size
that would get them where they want to be. It's not friendly to
present them with say 192 DPI, and when they want say 80% of that,
leave them to do the math. Or even asking them to relate the DPI to
physical inches (though I guess the DPI we're talking about here is
some intermediate virtual one?).

Large parts of the world did not grow up with inches. I know I'd have
a hard time to hold up my fingers to show an inch...

Elvis

PS. Nevermind that in the KDE version I'm using, it's actually not
possible to tweak the scale factor per screen under X11 in the kscreen
KCM, so I have to manually set QT_SCREEN_SCALE_FACTORS if I want to
dabble with that. But if I do want to dabble, I want to dabble in
percent. DS.

>
> --
> Matthew
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