[Development] Updated high-DPI support for Qt 5.14

[Elvis Stansvik]

Den ons 25 sep. 2019 kl 20:51 skrev Kai Pastor, DG0YT <dg0yt at darc.de>:
>
> Am 25.09.19 um 20:08 schrieb 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.
>
> There is nothing wrong with preferring simplicity for the most common
> case. But please provide a clear way how to get accurate sizes when
> desired, e.g. for 1:1 drawing or for print preview. With "clear"
> including uniform cross-platform.

Yes, absolutely, I want that use case to just work too of course. I
was speaking only of the "i want to change the size of buttons and
text on my computer" use case, not about print preview / desktop
publishing types of use cases (those are important too of course, and
should just work, irregardless of the user's desktop screen scaling
settings).

Elvis

>
> Kai
>
>
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