[Development] Qt 5.13 & 5.14 add device-independent pixels to device-dependent

Morten Sørvig Morten.Sorvig at qt.io
Thu Jan 30 15:34:02 CET 2020

> On 29 Jan 2020, at 04:14, Thiago Macieira <thiago.macieira at intel.com> wrote:
> On Tuesday, 28 January 2020 06:48:53 PST Morten Sørvig wrote:
>> There are several possible solutions:
>> 1) The scale factor for screen positions is 1: [the current choice]
>>  Simple to implement. Device-independent virtual geometry may now have
>>  “gaps”, unoccupied by any actual screen. This may come as as surprise
>>  but is not completely unprecedented: you can create gaps also by
>> arranging screens diagonally.
> Indeed, there are some conditions that are impossible to implement if you 
> tried to scale differently when three or more monitors are present and not 
> arranged linearly. Like in the case:
>  A   C
>  B
> If A is scaled and B isn't, then where does C start?

Exactly. In my opinion the only workable solution to this is that the 
user (end-user) arranges the screens in device-independent pixel space,
using the dialog provided by the OS/desktop environment.

macOS works this way, Windows doesn’t. I think the linux desktop environments
could work this way when using Wayland, but I’m not sure what actually do.
(The test is; does a 2x screen show up as a very large screen, or not)

If this holds then solving the problem completely is out-of-scope for Qt,
and we can settle on choosing the least-worst workaround.


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