[Development] Revisiting high-DPI configuration options

[Prav]

Hello, Everyone!

> The scope of this is the Qt::AA_EnanbleHighDpiScaling mode. I’d like to
> focus on two aspects:
>     1) Automatic scale factor configuration based on system settings.
There so many debates about this topic and how to get real DPI for all devices correctly.
But I personally does get this as SO important thing. And this is because people are different
and have different preferences about reading from screen (because of eyes or just personally).
Which brings me to understanding that it does not matter what is the DPI of screen. It matter only
how large PERSON want program font normally be.
So I would expect that the main intention in developing of apps should be moved toward giving
the user possibility to scale the app.
And you are done!

All this problems in getting correct DPI of screen would NOT be so painfull. Your phone or monitor or OS or something
resulted in incorrect scale factor? ... does not matter! ... increase/decrease scale factor for that app as you like ... and here you are ... having this app
comfortable for eyes and personal preferences (not for DPI of scrrent ... most people even do not know what it is and why they should care)!
App should remember of couse this setting to restore it back at restart

>     2) Handling fractional scale factors (rounding).
Previous idea need fractional scale factors to work ... FOR SURE!



PS I can give many more cases then getting right DPI does not give usability to user.
1. Developers or Designers are young, have good eyes are pretty conformable with small fonts.
    They produce app with HighDPI support which correctly scales to DPI of HighDPI user device. But ... this does not mean
    that old persons would feel comfortable with the app ... their eyes see not as good as when they were young.
2. Could be a reverse case ... like you want smaller because devs created app which seems larger to you.
3. Devs and Designers usually have good tech. I mean good monitors, modern phones with good crisp screen.
    But user's tablet/phone can be not modern or be cheap or with tons of scratches (for example with plastic (not glass screens)).
    Sooo ... visibility is much worse ... but DPI could be same.
4. You are OK with design and size of app's fonts at your notebook/tablet with like 10'', devs and designer see things the same good as you
    and your screen is modern and good with gorilla glass or something same and DPI scale factor was determined exactly as it is.
    But now you are inside city transport ... and guess what ...
    you are shaken! ... and this mean you see the screen worse ... you need to increase the scale!
    And if you sit/lay still in the bedroom you what smaller font to see more info at once.

I have nothing against getting right DPI at app's startup ...

I wanted just to say that I see that it is actually NOT THE MAIN PURPOSE! ... for usability!

May be Qt need to move accents from getting right DPI to making it user changeable ... FRACTIONALLY (as a good new practice)!
Like 10-20 % steps ... not just 2,3,4,5.

I do not see much trend in Qt-discussions/apps-interfaces about user-defined scale factor. But only THIS is important to user.
And NOT DPI ;)