QTextBrowser with transparent background

**MatuX** · 2010-07-22, 09:07

Hey guys,

I'm trying to make a QTextBrowser's background transparent. I googled solutions to this and found that I should setAutoFillBackground(false) the viewport() of my QTextBrowser instance.

That isn't doing anything in my case... I also tried setting the body style to 'background-color:transparent' but that won't do anything as well...

The background of the QWidget is drawn using paintEvent.

Am I doing something terribly wrong? Here is some of my code:

Code:

MyCustomWidget::MyCustomWidget(QWidget *parent) :
    QWidget(parent)
{
legalText = new QTextBrowser(this);
    legalText->setObjectName(QString::fromUtf8("legalText"));
    legalText->setGeometry(QRect(37, 184, 296, 344));
    legalText->setHtml(QString::fromUtf8("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0//EN\" \"http://www.w3.org/TR/REC-html40/strict.dtd\">\n"
                                         "<html>"
                                         "<head>"
                                            "<meta name=\"qrichtext\" content=\"1\" />"
                                            "<style type=\"text/css\">\n"
                                                "p, li { white-space: pre-wrap; }\n"
                                            "</style>"
                                         "</head>"
                                         "<body style='background-color:transparent'>\n"
                                            "<p align=\"justify\" style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">"
                                                "<span style=\" font-size:6pt; color:#c7c7c7;\">"
                                                    "My text"
                                                "</span>"
                                            "</p>"
                                         "</body>"
                                         "</html>"));
    legalText->viewport()->setAutoFillBackground(false);
}

void MyCustomWidget::paintEvent(QPaintEvent *paintEvent)
{
    QPainter painter(this);
    if( !background.isNull() )
        painter.drawPixmap(0, 0, background);
}

Everything is displayed perfectly, I have a couple of labels, the background and two custom buttons and they're all fine. This is my only issue!

Thanks a lot in advance!

**divanov** · 2010-07-22, 11:25

Did you try on other platforms and/or with other styles?
http://doc.qt.nokia.com/4.6/qapplication.html#setStyle

**MatuX** · 2010-07-23, 03:24

Originally Posted by divanov

Did you try on other platforms and/or with other styles?
http://doc.qt.nokia.com/4.6/qapplication.html#setStyle

Hey divanov, thank you for your reply. It seems you're always there to rescue me

After getting the list of available styles, I tried all of them, Windows, Motif, CDE, S60, Plastique and Cleanlooks. Not one of them seemed to do the trick. I also checked the setStyle returned value to see if the actual style was being set, and tried with both first letter upper case and all lower case.
Funny thing, when setting the "S60" style, it crashed...

I also tried several combinations of setAutoFillBackground, on the parent QWidget, its viewport, QTextBrowser and its viewport as well. I also tried setBackgroundRole(QPalette::NoRole);.

Any ideas? I'm banging my head at this, as widgets with transparent backgrounds should be something quite common on a Smartphone!

Best!

**MatuX** · 2010-07-23, 03:31

Is there any other Control to show multilined text anyways? Perhaps since this uses HTML it has its added complexities...

**MatuX** · 2010-07-23, 04:04

I managed to fix this using StyleSheets.

The strange thing is that a StyleSheet with "background-color: transparent;" or "background-color: rgba(0, 0, 0, 0);" wouldn't make the background transparent. But when I tried a random gradient, voila! The background was transparent!
So, I simply grabbed the linear black to white gradient from Qt Designer, got it from the autogenerated .h and placed in my QWidget like this:

Code:

my_qwidget->setStyleSheet(QString::fromUtf8("background-color: qlineargradient(spread:pad, x1:0, y1:0, x2:1, y2:0, stop:0 rgba(0, 0, 0, 0), stop:1 rgba(255, 255, 255, 0));"));

That seemed to do the trick! Now my background is transparent.

The only left issue is that now I get a world of Painter not active errors or warnings in the console. Some examples:
QPainter::begin: Paint device returned engine == 0, type: 3
QPainter::setWorldTransform: Painter not active
QPainter::worldTransform: Painter not active
QPainter::setBrush: Painter not active
QPainter::setRenderHint: Painter must be active to set rendering hints

And so on, and so on.

Since I'm still a newbie in Qt, I really can't decipher those errors. Perhaps there is something Very wrong going on, but everything seems to be working just fine on the Simulator and the actual Phone.

Hope this quasi-solution helps anyone with my same issue, though.

Thanks!

**divanov** · 2010-07-23, 08:12

QPainter::begin() has failed for some reason. Could be that some other QPainter is already painting on the same device.
http://doc.trolltech.com/4.6/qpainter.html#begin

**srikanthsombhatla** · 2010-07-23, 09:08

If you want to make only your textbrowser transparent you can use QGraphicsOpacityEffect on it. But it will make it transpatent wrt to its parent window base color. So it you want a complete transparency, make the parent window also transparent, by using a setAttribute(Qt::WA_TranslucentBackground, true). Unfortunely you have to make it frameless windows to get the transparency effect.

**divanov** · 2010-07-23, 09:22

Originally Posted by srikanthsombhatla

If you want to make only your textbrowser transparent you can use QGraphicsOpacityEffect on it.

You forgot to mention that one should be using QGraphicsView for that.

**srikanthsombhatla** · 2010-07-24, 09:05

QGraphicsEffect can be applied on any QWiget also using QWidget::setGraphicsEffect(), only requirement is that the effect should not be a stack variable.

**MatuX** · 2010-07-30, 08:55

Hey!

I tried to do what you said, but that makes the whole Widget semi-transparent, I only want the Background of that control to be transparent.

I'm still using my style sheet solution and the Paint errors are still there

Thanks anyways!

**danhicksbyron** · 2010-07-30, 13:48

There are a bunch of widget attributes you can set that manipulate the transparency of the widgets. They're rather arcane, and some are platform-specific, though.

See "Transparency and Double Buffering" in the QWidget doc, and also http://doc.qt.nokia.com/4.6-snapshot...Attribute-enum .

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