Broken rendering of Vectorscope

[michaelgregorius]

System Information

Linux - Wayland

LMMS Version(s)

1825208

Bug Summary

The Vectorscope plugin renders in a broken way on a Linux Wayland system:

Bildschirmaufnahme_20240925_170936.webm

Steps To Reproduce

1. Add a Vectorscope as an effect.
2. Open the view of the Vectorscope.

Please search the issue tracker for existing bug reports before submitting your own.

• I have searched all existing issues and confirmed that this is not a duplicate.

[michaelgregorius]

It works under X11 and therefore only is a problem under Wayland. It is caused by the calls to devicePixelRatio() here:

lmms/plugins/Vectorscope/VectorView.cpp

Line 254 in 1825208

temp.setDevicePixelRatio(devicePixelRatio());

And here:

lmms/plugins/Vectorscope/VectorView.cpp

Line 256 in 1825208

temp.scaledToWidth(displayWidth * devicePixelRatio(),

The method devicePixelRatio() returns 2 on my system whereas I have set my scaling to 125%, i.e. 1.25. The following code fixes the rendering on my machine:

//temp.setDevicePixelRatio(devicePixelRatio());
painter.drawImage(displayLeft, displayTop, temp.scaledToWidth(displayWidth, Qt::SmoothTransformation));

It might break another case though? I am not sure why it is necessary to use the device/pixel ratio here.

[michaelgregorius]

There's also a problem with the general functionality under Wayland. The screen is not cleared if HQ mode is disabled but everything works in HQ mode:

Broken.Vectorscope.in.Non-HQ.webm

[michaelgregorius]

With the fix described above the broken rendering starts to appear when the value of the variable displayWidth is equal or greater than activeSize.

[bratpeki]

I noticed, on latest master, than it occurs only with a persistence of 1. This is expected, as I would believe there is no persistance for a value of 1 (that is 100%).

[michaelgregorius]

Did you test it under Linux with Wayland, @bratpeki? It seem that upscaling pixmaps does not work on that platform like it works on X11.

[bratpeki]

No, this is on Windows, works just fine!