ui/virtualconsole: fix background colour issues

[jpue]

Reported at https://www.qlcplus.org/forum/viewtopic.php?t=19491, fixes #1986

Describe the bug / To Reproduce
QLC+ 4.14.4 unintentionally introduced breaking changes to the background colour/background image of the Virtual Console (see forum or linked issue for details).

Expected behaviour
The existing functionality of QLC+ 4.14.3 and earlier versions should not be changed (see forum or linked issue for details).

Problem Analysis
Since there have been no changes to the relevant parts of the QLC+ source code, the breaking changes are likely located in the Qt framework.

The following versions/platforms seem to be affected:

• official QLC 4.14.4 on Windows (11) / Qt 6.10.2
• current master branch build on Ubuntu 25.04 (Qt 6.8.3), 25.10 (Qt 6.9.2) and 26.04 beta (Qt 6.10.2)

The following versions/platforms do NOT seem to be affected:

• official QLC 4.14.3 on Windows / Qt 6.8.1
• current master branch build on Ubuntu 22.04 (Qt 5.15.3)

Proposed Solutions
As described in this Qt example, the autoFillBackground property of QWidget seems to be important for a solid background colour to be drawn.
Although the constructor of VCWidget also sets this to the correct value (true), this property is reset to false for the VC main VCFrame called m_contents at some point after initialisation.
To be honest, I could not find the exact cause of this, but re-setting it to true when a new colour or image is set, as well as setting this property for the parent widget (m_scrollArea) when it is created (source for this idea), fixes the issues and restores the previous behaviour.

For (Linux) Qt5 builds (which were not affected anyway), this changes nothing.

Please note that I only developed this on Linux, so it still needs to be tested on Windows and macOS builds.

When this PR is merged, the Qt version of Linux v4 builds in the GitHub Actions can be bumped to 6.10.2 again to match the other platforms.

[coveralls]

coverage: 34.068% (-0.001%) from 34.069% — jpue:vc_backgroundColour into mcallegari:master

[mcallegari]

Hi @jpue thanks for this.
Unfortunately this patch is not enough to fix the issue.
I am testing on Windows, since it is the most used platform and where the issue is more evident.
Building with Qt 6.11 this is what I get with your patch

Design mode:

Operate mode:

3 cases:

• Virtual console background shows only the border in design and full color in operate mode
• a VC frame shows the border in design mode and the border again in operate mode
• a VC Button seems to be OK, since the background painting is customized

I have alreasy spent some time before your patch and decided to release 4.14.5 on Qt 6.9.x until a fix is found

[jpue]

Ok, fine.

I am still wondering whether this is an issue that could even be fixed in the QLC+ source code, or rather a change/regression in the Qt library.

It is up to you, of course, if we keep this open as a reminder of an ongoing issue or close it, since it does not actually the problem.

As you mentioned QLC+ 4.14.4 being released with Qt 6.9.x: Unfortunately, I have not had a chance to test QLC+ 4.14.4 (it was just released before a larger show I did), but I remember there were audio issues on Windows with Qt 6.8.2 and higher.
Your bug report (QTBUG-136057) is still linked on the QLC Plus 5 build HOWTO wiki page.
Although the Qt developers mention a patch they have merged into Qt 6.9.1 (and backported to 6.8.4), the issue is not marked as resolved.
So is the issue still present?

[mcallegari]

The v5 video tutorials are made on Windows and the last one I did about audio/video was all fine with Qt 6.10.
I think most of the audio issues have gone in recent Qt versions.
There still might be corner cases with specific sample rates or mono files. Can be resolved by converting the audio files though.
In any case this issue remains, so sooner or later we'll have to sort it out (unless it's a Qt regression....)