Adding a QProgressbar makes my app cpu consumption pass from 0% to 75-80% of a core

[aidaqt]

Hi,

I'm adding a small QProgressbar to my app, but now I'm realizing that it is taking almost a core. I've read about some bugs related but I cant fix or workaround this issue. Any chances?

-QT 4.8.4
-Windows 7

[Chris Kawa]

Maybe you just update it too frequently? Some code would be useful.

[aidaqt]

I never update it, it is only a default QProgressBar added with the QT Designer.

[aidaqt]

@int main(int argc, char *argv[])
{
QApplication a(argc, argv);
pruebasqt w;

QGraphicsDropShadowEffect* wndShadow = new QGraphicsDropShadowEffect;
wndShadow->setBlurRadius(9.0);
wndShadow->setColor(QColor(0, 0, 0, 90));
wndShadow->setOffset(5);
w.setGraphicsEffect(wndShadow);

w.setWindowFlags( Qt::FramelessWindowHint | Qt::WindowMinimizeButtonHint);
w.setAttribute(Qt::WA_TranslucentBackground);

w.setStyleSheet("QWidget{ background: red;}");

w.show();
return a.exec();
}
@

Being "pruebasqt" a default QMainWindow with one QProgressBar. This makes 100% of one core in my computer (An Intel Xeon with 8 cores and 26 Gb RAM)

[aidaqt]

Can anyone reproduce this behaviour? I think this could be a bug.

[JKSH]

Hi,

Does it still happen if you upgrade to Qt 4.8.5?

What happens if you delete lines 6 to 15?

What happens if you don't add the QProgressBar?

What are the related bugs that you've found?

[aidaqt]

https://bugreports.qt-project.org/browse/QTBUG-20880

The problem appears when combining the setGraphicsEffect with a QProgressBar. Can you reproduce this?

[aidaqt]

Full compilable version:

@
#include <QtGui/QApplication>
#include <QGraphicsDropShadowEffect>
#include <QProgressbar>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);

QWidget* w = new QWidget();
w->setGeometry(40,40,1600,1000);
QProgressBar* qp = new QProgressBar(w);
qp->setValue(99);

QGraphicsDropShadowEffect* wndShadow = new QGraphicsDropShadowEffect;
w->setGraphicsEffect(wndShadow);

w->show();
return a.exec();
}
@