QPainter does not paint on QPrinter on release build

Enym

Hello,

On a debug build painting works fine. I tried building with both MSVC and MinGW.

Here's a code snippet:

void ReportPrinter::ShowPreviewDialog(QPrinter::OutputFormat format) {
    m_printer.setOutputFormat(format);

    QString selectedPageSize = m_pageSizeCombobox->currentText();

    if (selectedPageSize == "A4") {
        m_printer.setPageSize(QPrinter::A4);
    } else if (selectedPageSize == "A3") {
        m_printer.setPageSize(QPrinter::A3);
    } else if (selectedPageSize == "A2") {
        m_printer.setPageSize(QPrinter::A2);
    } else if (selectedPageSize == "A1") {
       m_printer.setPageSize(QPrinter::A1);
    } else if (selectedPageSize == "A0") {
        m_printer.setPageSize(QPrinter::A0);
    }


    QPrintPreviewDialog prevDlg(&m_printer, nullptr, Qt::Window);
    connect(&prevDlg, SIGNAL(paintRequested(QPrinter*)), this, SLOT(DrawOnPrinter(QPrinter*)));
    prevDlg.exec();
}


void ReportPrinter::DrawOnPrinter(QPrinter *printer) {
    QPainter painter;
    painter.begin(printer);

    qDebug() << "painterIsActive: " << painter.isActive(); // returns true on debug build and false on release build
    // painting code ....
}

Thanks in advance.

mrjj

Hi
Qt version is also important :)

Enym

Qt version: 5.7.

jsulm

@Enym Does painter.begin(printer) return false? printer is not null in DrawOnPrinter (shouldn't be, but still worth checking)?

Enym

Had a painter.begin() call in Q_ASSERT, which is obviously disabled in a release build. Stupid me :)

Q_ASSERT(painter.begin(printer));

jsulm

@Enym Yes, don't put production code into asserts :-)