@denistu
After I read the source code, I found that when a widget with QGraphicsEffect executes the render method, the internal call to QGraphicsEffect's draw method will call the sourceWidget's render method again. However, there's an internal judgment in the render method that causes the sourceWidget to return. So, you can see that using the target widget's render method directly doesn't work. So, all we have to do is figure out a way to call the widget's render method indirectly.We can set a container widget as the parent widget for the widget and just call the container widget's render method. That'll execute the render methods of all child widgets.I hope this helps.
void QWidget::render(QPainter *painter, const QPoint &targetOffset,
const QRegion &sourceRegion, RenderFlags renderFlags)
{
....
Q_D(QWidget);
const bool inRenderWithPainter = d->extra && d->extra->inRenderWithPainter;
const QRegion toBePainted = !inRenderWithPainter ? d->prepareToRender(sourceRegion, renderFlags)
: sourceRegion;
if (toBePainted.isEmpty())
return;
if (!d->extra)
d->createExtra();
d->extra->inRenderWithPainter = true;
....
}
https://code.qt.io/cgit/qt/qtbase.git/tree/src/widgets/kernel/qwidget.cpp#n5316
QPixmap QWidgetEffectSourcePrivate::pixmap(Qt::CoordinateSystem system, QPoint *offset,
QGraphicsEffect::PixmapPadMode mode) const
{
....
// call render() again, so would retrun and the pixmap is only transpant with nothings.
m_widget->render(&pixmap, pixmapOffset, QRegion(), QWidget::DrawChildren);
....
}
https://code.qt.io/cgit/qt/qtbase.git/tree/src/widgets/kernel/qwidget.cpp#n6040
