sddm black screen on tv screen with AA_EnableHighDpiScaling

[ynsta]

SDDM stay on black screen when started on my TV screen with nvidia drivers 370.28-1.

After investigation I found that the screen geometry is wrongly reported by Qt when QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling); is used.

Removing this line in GreeterApp.cpp permits sddm to start properly.

with QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling):
Geometry: 0 0 -2147483648 x -2147483648
Logical DPI: inf
Logical DPI X: inf
Logical DPI Y: inf
Physical DPI: -4.7349e+07
Physical DPI X: -3.40913e+07
Physical DPI Y: -6.06068e+07
Physical size: 1600 x 900 mm

without:
Geometry: 0 0 1920 x 1080
Logical DPI: 30.0029
Logical DPI X: 29.9926
Logical DPI Y: 30.0131
Physical DPI: 30.48
Physical DPI X: 30.48
Physical DPI Y: 30.48
Physical size: 1600 x 900 mm

It might be a Qt bug but It could be interesting to add a verification on sddm-greater to remove this flag when dpi are wrongly reported.

My Xorg is 1.18.4 and Qt is 5.7.0 from archlinux.

[plfiorini]

@ynsta What Xorg and Qt versions are you running?

[ynsta]

@plfiorini Xorg 1.18.4 and Qt 5.7.0 from archlinux.

I also use nvidia drivers 370.28 and I can provide the edid of my screen if needed.

I have the same configuration on a second computer connected to a classic monitor without any issue.

[ynsta]

Maybe you should add a configuration option that permits to disable hidpi autoscale, it seems to be also the source of issue #692

[ynsta]

I made a pull request to add this option if you want.

#701

[plfiorini]

Good idea

[plfiorini]

Anyway that negative geometry is funny, looks like Qt cannot determine the screen resolution or Xorg reports an invalid one.
Just out of curiosity, @ynsta is the physical size correct?