How to set QPdfView's viewport background color?

[CPPUIX]

I'm trying to set a QPdfView's viewport background color, but unlike QAbstractScrollArea (from which QPdfView's derived), using stylesheet does not work.

Here's how I tried to do that:

#include <QApplication>
#include <QPdfView>

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

    QPdfView *pdfView = new QPdfView();

    pdfView->setMinimumSize(100,100);
    //I tried to set stylesheet in different ways, in multiple combinations
    //but none worked
    //pdfView->setStyleSheet("background: white");
    pdfView->setStyleSheet("QWidget{background: white;}");
    //pdfView->viewport()->setStyleSheet("background: white");

    pdfView->show();

    return a.exec();
}

Note: You need to to find and target PdfWidgets, so modify your CMakeLists.txt according the below, to be able to use QPdfView:

find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Widgets PdfWidgets)
find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS Widgets PdfWidgets)

target_link_libraries(MyExperiments PRIVATE
     Qt${QT_VERSION_MAJOR}::Widgets
     Qt${QT_VERSION_MAJOR}::PdfWidgets)

Here's how it looks, viewport is grey, and you can see the white background of QPdfView on the borders:

I also tried to change the background color of viewport by overriding QAbstractScrollArea::paintEvent, and here's how:

void paintEvent(QPaintEvent *event)
{
    QPdfView::paintEvent(event);

    QPainter p(viewport());
    QRect rect = viewport()->rect();

    rect.adjust(-1,-1,0,0);
    p.setBrush(QBrush(QColor(0,0,100)));
    p.drawRect(rect);
}    

But that ended up painting over viewport, not changing its background color, so it covers open documents, because If I use a transparent color, I can see the document through it.

I'm open to either or other ways, but I'd like to avoid using paintEvent if possible.

[ChrisW67]

@Pl45m4 That does not work here. The viewer appears to fill its viewport widget interior with a default dark grey. So, these do not fly:

QPdfView view;
view.setStyleSheet("QWidget {background-color: lime;} ");
// ^^ Results in a thin green line at the edges of the grey fill
view.viewport()->setStyleSheet("background-color: lime;");
// ^^ No visible effect at all

Even replacing the viewport with a generic widget or setting the palette QPalette::Window brush does not appear to achieve the goal.

Edit: Inspection of the QPdfView source leads to this result:

#include <QApplication>
#include <QPdfView>
#include <QPalette>

int main(int argc, char **argv) {
        QApplication app(argc, argv);
        QPdfView view;
        QPalette palette = view.palette();
        palette.setBrush(QPalette::Dark, QColor("lime"));
        view.setPalette(palette);
        view.show();
        return app.exec();
}

[Pl45m4]

@Abderrahmene_Rayene

Have you tried what is described here?

• https://doc.qt.io/qt-6/stylesheet-examples.html#customizing-qabstractscrollarea

Note: You have background and the example says background-color.

That painting the viewPort with a brush covers other content should be clear :)

[ChrisW67]

@Pl45m4 That does not work here. The viewer appears to fill its viewport widget interior with a default dark grey. So, these do not fly:

QPdfView view;
view.setStyleSheet("QWidget {background-color: lime;} ");
// ^^ Results in a thin green line at the edges of the grey fill
view.viewport()->setStyleSheet("background-color: lime;");
// ^^ No visible effect at all

Even replacing the viewport with a generic widget or setting the palette QPalette::Window brush does not appear to achieve the goal.

Edit: Inspection of the QPdfView source leads to this result:

#include <QApplication>
#include <QPdfView>
#include <QPalette>

int main(int argc, char **argv) {
        QApplication app(argc, argv);
        QPdfView view;
        QPalette palette = view.palette();
        palette.setBrush(QPalette::Dark, QColor("lime"));
        view.setPalette(palette);
        view.show();
        return app.exec();
}

[CPPUIX]

@Pl45m4 said in How to set QPdfView's viewport background color?:

That painting the viewPort with a brush covers other content should be clear

It's my first timing overriding a paintEvent and trying to use a QPainter to paint a widget, it only clicked in my head after I kept messing with it.

Thanks for you input!

[CPPUIX]

@ChrisW67 Thank you! That does the trick, it fills the background without obscuring the open document, and I don't have to use paintEvent!

Here's how it looks:

[CPPUIX]

@ChrisW67

I have a follow up question, just trying to understand.

Why is it needed to match the palette's color role with the one used in QPdfView's paintEvent?

I messed with it, and only QPalette::Dark seems to work.

Just curious, I could move on without an answer if it's not possible to provide one.

Thanks again!

[ChrisW67]

@Abderrahmene_Rayene The first couple lines in the QPdfView::paintEvent() do this:

QPainter painter(viewport());
painter.fillRect(event->rect(), palette().brush(QPalette::Dark));

Create a painter on the widget's viewport() and fill it using whatever brush is in the current palette' s QPalette::Dark position. This palette entry is hard-coded in QPdfView so the only control you have is to change the view (or viewport()) palette's QPalette::Dark entry.

[CPPUIX]

@ChrisW67 Thanks a lot! This clarifies it for me.