[Development] Qt 6 not seeing the same DPI as Qt 5

Henry Skoglund henry at tungware.se
Mon Nov 29 18:19:36 CET 2021


On 2021-11-29 17:41, Thiago Macieira wrote:
> I'll probably have to report this as a bug, but just in case someone has seen
> it before:
>
> $ diff -u qtdiag5 qtdiag6
> [...]
>     Geometry: 1920x1200+0+0 (native: 3840x2400+0+0) Available: 1920x1200+0+0
>     Virtual geometry: 5760x1200+0+0 Available: 5760x1200+0+0
>     2 virtual siblings
> -  Physical size: 288x180 mm  Refresh: 59.9939 Hz Power state: 0
> -  Physical DPI: 169.333,169.333 Logical DPI: 120.118,120 (native:
> 240.236,240) Subpixel_None
> +  Physical size: 406x228.6 mm  Refresh: 29.9806 Hz Power state: 0
> +  Physical DPI: 120.118,120 Logical DPI: 96,96 Subpixel_None
>     High DPI scaling factor: 2 DevicePixelRatio: 2
>
> Qt 5 agrees with xrandr:
> $ xrandr | grep eDP-1
> eDP-1 connected primary 3840x2400+0+0 (normal left inverted right x axis y
> axis) 288mm x 180mm
>
> I start X with the "-dpi 240" setting, which gives me the best font size to
> work on either display. Qt 5 obeys it just fine, dividing it by 2 because of
> the scale factor, so my desktop looks fine. However, the one Qt 6 application
> I use (Qt Creator) does not and has tiny fonts. I can override it with
> QT_FONT_DPI=240 in the environment, but shouldn't have to.
>
> That logical DPI of 96 makes zero sense. It's not physically correct and is
> not part of the X config. Where is it coming from?
>
> What's changed between 5 and 6?
>

Slightly offtopic but did you build your own Qt Creator using Qt 6?
(The downloadable vanilla 5.0.3 is based on Qt 5.15.2).



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