QTextEdit with semi-transparent background

[ber_44]

I have the following code to paint a semi-transparent label on an image and then write on that label:

topLabel = new QTextEdit(imageLabel); 
//   topLabel->setAttribute(Qt::WA_NoSystemBackground);
   QPalette palette;
   // a white semi-transparent background
   palette.setColor(QPalette::Window, QColor(255, 255, 255, 127));
   topLabel->setPalette(palette);
   topLabel->setText(*text);

topLabel = new QTextEdit(imageLabel); 
//   topLabel->setAttribute(Qt::WA_NoSystemBackground);
   QPalette palette;
   // a white semi-transparent background
   palette.setColor(QPalette::Window, QColor(255, 255, 255, 127));
   topLabel->setPalette(palette);
   topLabel->setText(*text);

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It creates a white, opaque background.
It topLabel is QLabel, it creates a transparent background.
In any case, it is not semi-transparent.

[marcel]

I have the following code to paint a semi-transparent label on an image and then write on that label

I don't quite understand what you mean? A transparent label background?
Why don't you do this in the paintEvent of your label? Fill it with a semitransparent pixmap, and then draw on it whatever you want...

Regards.

[ber_44]

I mean a semi-transparent label background -- i.e. 50% white, 50% transparent.
According to the QWidget doc, "The background can be set using ... setPalette()."
So I'm hoping to avoid subclassing QStyle.
The size of the background can be changed, so a semi-transparent pixmap won't work.

[marcel]

You can always scale the pixmap, being transparent and all... And I didn't mean subclassing QStyle, but QLabel. I have tried this method before, and it works.

[ber_44]

Since it is only SEMI-transparent (that is, partially opaqe), scaling will give bad resolution.
Well, true that you can use a huge-huge pixmap and scale it down, but that's not very efficient.

[marcel]

Transparent pixmap, means only alpha channel, so no scaling effects occur.
Is this what you're trying to achieve?

void CTestLabel::paintEvent( QPaintEvent* )
{
    QPainter p( this );
    QPixmap pix( 1, 1 );
    pix.fill( Qt::transparent );
    p.drawPixmap( rect(), pix );
    p.setOpacity( 0.5 );
    p.fillRect( rect(), Qt::white );
 
    p.setOpacity( 1 );
    p.drawText( rect(), "test" );
};

void CTestLabel::paintEvent( QPaintEvent* )
{
    QPainter p( this );
    QPixmap pix( 1, 1 );
    pix.fill( Qt::transparent );
    p.drawPixmap( rect(), pix );
    p.setOpacity( 0.5 );
    p.fillRect( rect(), Qt::white );

    p.setOpacity( 1 );
    p.drawText( rect(), "test" );
};

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I get a white label, 50% opaque, with some text on it.

[jpn]

palette.setColor(QPalette::Window, QColor(255, 255, 255, 127));

palette.setColor(QPalette::Window, QColor(255, 255, 255, 127));

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Shouldn't that be QPalette::Base: "Used as the background color for text entry widgets; usually white or another light color"?