Setting 'border-top' property for QMdiArea in style.css causes LMMS to freeze when maximizing any subwindow

[z-up]

System Information

Windows 10

LMMS Version(s)

lmms-1.3.0-alpha.1.102+g89fc6c960-mingw-win64

Most Recent Working Version

No response

Bug Summary

Setting 'border-top' property for QMdiArea in style.css causes LMMS to freeze when maximizing any subwindow (like Piano Roll or Song Editor)

Expected Behaviour

Not freezing

Steps To Reproduce

1. Set border-top property for QMdiArea in style.css (e.g. border-top: 1px solid black;)
2. Open LMMS
3. Maximize Song Editor
4. Try changing horizontal zooming, for example

Logs

Click to expand

Screenshots / Minimum Reproducible Project

No response

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

[michaelgregorius]

I can reproduce this. If I manually break execution with a debug build I very often land in the following method/context of TrackContentWidget::

[...]
QPainter::drawLine(QPainter * const this, const QLineF & l) (/usr/include/qt/QtGui/qpainter.h:531)
lmms::gui::TrackContentWidget::updateBackground(lmms::gui::TrackContentWidget * const this) (/home/michael/Eigene Dateien/Development/LMMS/lmms-dev-mg/lmms/src/gui/tracks/TrackContentWidget.cpp:145)
lmms::gui::TrackContentWidget::resizeEvent(lmms::gui::TrackContentWidget * const this, QResizeEvent * resizeEvent) (/home/michael/Eigene Dateien/Development/LMMS/lmms-dev-mg/lmms/src/gui/tracks/TrackContentWidget.cpp:647)
libQt5Widgets.so.5!QWidget::event(QEvent*) (Unbekannte Quelle:0)
[...]

Due to the fact that only a CSS property of Qt's QMdiArea is changed I wonder if it some strange update conflict/loop between the QMdiArea and its children.