QT_SCALE_FACTOR? Qt5 applications are not scaled according to output->scale

[birdie-github]

I'm using audacious built against Qt5 in Fedora 39, Wayfire 0.8.

Here's my output section:

[output:eDP-1]
mode = 2560x1600@120.000999
position = 0,0
transform = normal
scale = 1.333

When I start audacious everything in it looks very small, as if it's not scaled to 1.333.

I've googled and found this: https://doc.qt.io/qt-5/highdpi.html

With QT_SCALE_FACTOR=1.333 audacious the application get scaled.

My question is, what about exporting scale as QT_SCALE_FACTOR for newly run applications?

But then scale can be changed dynamically and I've no idea how it can be propagated to already running Qt5 applications.

[soreau]

Does QT_WAYLAND_FORCE_DPI=physical help?

[birdie-github]

Does QT_WAYLAND_FORCE_DPI=physical help?

Nothing changes.

[soreau]

Does weston-info show the correct scale value for the wl_output?

[birdie-github]

Fedora doesn't have such a command/binary:

dnf whatprovides '*/weston-info'
Error: No matches found. If searching for a file, try specifying the full path or using a wildcard prefix ("*/") at the beginning.

[ammen99]

The program was renamed to wayland-info in the newer releases.

[birdie-github]

No idea what I'm looking for.

Here's the entire dump:

wayfire-info.zip

[soreau]

It looks like wayfire/wlroots is setting the scale correctly. Does this problem happen with all Qt clients or just some? Seems like this used to be a problem with sway too.

[birdie-github]

QBitTorrent using Qt 6.5.2 is affected as well though I was sure Qt 6 perfectly supports fractional scaling.

GoldenDict using Qt 5 just crashes:

goldendict 
qt.qpa.xcb: could not connect to display 
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, xcb.

Aborted (core dumped)

[soreau]

Hm, maybe you're using Qt apps with xwayland sometimes because the wayland backend isn't used? What happens if you set QT_QPA_PLATFORM=wayland for these cases?

[ammen99]

@birdie-github If you have a problem with a wayland-native application, please run it with WAYLAND_DEBUG=1 and post the log (it will spit out quite a lot of information), this way we can verify that this is indeed a client bug (or if not, it will tell us what is missing on Wayfire's side).

[birdie-github]

I don't have XWayland installed.

wayland-debug-audacious.zip

[soreau]

What if QT_ENABLE_HIGHDPI_SCALING=1 is set? According to the Qt docs, "The QT_ENABLE_HIGHDPI_SCALING environment variable, introduced in Qt 5.14, enables automatic scaling based on the pixel density of the monitor."

[ammen99]

@birdie-github I looked at your log again and it seems that Wayfire tells the client that the output should be scaled, the client acknowledges this, but then doesn't scale its font size internally - which would be a problem of the application. Unfortunately I'm not sure what could cause this and whether there are workarounds for this, but it isn't something we can fix on the Wayfire side.