[Development] Updated high-DPI support for Qt 5.14

Thiago Macieira thiago.macieira at intel.com
Thu Sep 26 04:48:26 CEST 2019

On Wednesday, 25 September 2019 05:54:20 PDT 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)

Assume no one will ever call that function. What's the outcome?

Also, DPIs are a physical property of the monitor, but they don't account for 
my distance to it. Previously, I only needed one parameter to toggle, which 
was either 1 or 2. Now, in order to properly configure, I need to find out 
what the current DPI is and then update it.

Moreover, I can have two different monitors connected to the same output (at 
different times, of course). Since they have different DPI, the multiplicative 
factor allows me to set it once for both, but if I set a DPI setting, it'll 
likely be wrong for at least one of them.

> > Anyway, what's the correct way to specify now that one of my external
> > monitors  is highdpi but the other isn’t?
> The correct way would be to configure the windowing system. Qt would then
> pick up the configuration via the platform plugin.

Agreed, but for those of us still on X11, that's not na option.
> In practice, the environment variables you are currently using may be your
> best option on X11. 

Ok, thanks. This becomes the recommendation for KDE Plasma Shell configuration 
for X11 then: continue using the variables as they are.
> 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.

Sure, but where, on X11?

Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel System Software Products

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