Semi-transparent QDialog is not semi-transparent anymore

l3u_

Hi :-)

Some time ago, I wrote a dialog (for KPhotoAlbum, cf. https://cgit.kde.org/kphotoalbum.git/tree/AnnotationDialog/ProposedFaceDialog.cpp ) which appears semi-transparent. I implemented it, according to https://wiki.qt.io/QWidget_Semi-transparent_Background_Color in the following way:

.h:

protected:
    void paintEvent(QPaintEvent *);

.cpp:

void AnnotationDialog::ProposedFaceDialog::paintEvent(QPaintEvent *)
{
    QColor backgroundColor = Qt::white;
    backgroundColor.setAlpha(160);
    QPainter painter(this);
    painter.fillRect(rect(), backgroundColor);
}

which worked just fine. I however noticed today that this is not the case anymore: the widget appears grey and opaque. I'm not sure when this happened, but it's definitely the case with Qt 5.7.1.

I would greatly appreciate all help on how to fix this!

Cheers, Tobias

SGaist

Hi,

Can you check whether it's still the case with a more recent version 5.9.2 is around the corner.

l3u_

Unfortunately, Qt 5.9.2 is not yet available on Gentoo. I'll check it as soon as possible.

mrjj

Hi
Qt 5.9 on windows 10
alt text

Buckwheat

Hi @l3u_

Have you tried adding:

setAttribute (Qt::WA_TranslucentBackground);

into the constructor of MyDialog?

I had similar problems where my dialogs and frames were "sort-of" transparent and this fixed them.

J.Hilk

@l3u_

I recently made a custom Messagebox with a semitransparent background. I had a slightly different approach:

//Because the baseclass is a QWidget:
protected:
    virtual void paintEvent(QPaintEvent *)Q_DECL_OVERRIDE{
        QStyleOption opt;
        opt.init(this);
        QPainter p(this);
        style()->drawPrimitive(QStyle::PE_Widget, &opt, &p, this);
    }

//Because its a Qt-Designer-Form-Class I use a StyleSheet:
this->setObjectName("myMessage");
this->setStyleSheet("QWidget#myMessage{background-color:rgba(94,122,135,220);}");

No problems at all with that.
Used: Qt 5.9.1