setting application wide font with

    QApplication app(argc, argv);
    int fontId = QFontDatabase::addApplicationFont(":/fonts/SourceCodePro-Light.ttf");
    // int fontId = QFontDatabase::addApplicationFont(":/fonts/lte50331.ttf");

    if (fontId != -1) {
        // Get the font family name
        QStringList fontFamilies = QFontDatabase::applicationFontFamilies(fontId);

        if (!fontFamilies.isEmpty())

{             QString fontFamily = fontFamilies.at(0);             // Create and set the font             QFont customFont(fontFamily);             customFont.setPointSize(10); // Optional: set size             app.setFont(customFont);         }

    } else

{         qWarning() << "Failed to load custom font from resources";     }

results in random black areas while printing with KDReports or 

    QPrinter printer;
    printer.setFontEmbeddingEnabled(true);

    // Show print dialog
    QPrintDialog dialog(&printer, this);
    if (dialog.exec() == QDialog::Accepted)

{         // Print the content         ui->textEdit->print(&printer);     }