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Explaining Qt GUI's QPagedPaintDevice::PdfVersion (enum) for PDF Generation


Purpose

This enumeration (enum) in Qt's GUI framework defines the possible versions of PDF files that can be generated using classes like QPrinter and QPdfWriter. These classes are derived from the base class QPagedPaintDevice and are used for creating printable output or exporting content to PDF format.

Enumeration Values

The PdfVersion enum consists of the following values:

  • QPagedPaintDevice::PdfVersion_1_6 (introduced in Qt 5.12): This value creates a PDF that conforms to the PDF 1.6 specification. This version offers additional features compared to 1.4, such as support for embedded fonts and advanced encryption.
  • QPagedPaintDevice::PdfVersion_A1b: This value indicates that the PDF will adhere to the PDF/A-1b standard. This standard is specifically designed for archiving purposes and ensures that the PDF remains readable over long periods, even if the software used to create it is no longer available.
  • QPagedPaintDevice::PdfVersion_1_4: This value specifies that the generated PDF will comply with the PDF 1.4 specification. This is a widely supported version and ensures compatibility with a broad range of PDF viewers and software.

Choosing the Right Version

The appropriate PdfVersion to use depends on your specific requirements:

  • If you require advanced features like embedded fonts or stronger encryption (available since Qt 5.12), go with PdfVersion_1_6.
  • If your PDF needs to be archived for long-term readability, select PdfVersion_A1b.
  • If compatibility with the most viewers is paramount, choose PdfVersion_1_4.

Setting the PDF Version

You can control the PDF version using the following methods of classes derived from QPagedPaintDevice:

  • QPdfWriter::setPdfVersion() for QPdfWriter objects
  • QPrinter::setPdfVersion() for QPrinter objects
#include <QPrinter>

int main() {
    QPrinter printer;

    // Set the PDF version to 1.4
    printer.setPdfVersion(QPrinter::PdfVersion_1_4);

    // ... (other printer settings)

    printer.print("your_output.pdf");
    return 0;
}

Setting PDF Version with QPrinter

#include <QPrinter>
#include <QTextDocument>

int main() {
    QTextDocument document;
    document.setHtml("<p>This is some content to be printed as PDF.</p>");

    QPrinter printer;
    printer.setOutputFormat(QPrinter::PdfFormat);

    // Set the PDF version to A1b for archiving
    printer.setPdfVersion(QPrinter::PdfVersion_A1b);

    printer.setOutputFileName("archived_document.pdf");
    document.print(&printer);

    return 0;
}

In this example, a QTextDocument is created with some HTML content. A QPrinter object is then configured to output the document as a PDF file. The setPdfVersion method is used to set the PDF version to PdfVersion_A1b for archiving purposes. Finally, the setOutputFileName method specifies the output filename, and the print method initiates the PDF generation process.

Setting PDF Version with QPdfWriter

#include <QPdfWriter>
#include <QPainter>

int main() {
    QPdfWriter writer("custom_layout.pdf");
    writer.setPageSize(QPageSize::A4);

    // Set the PDF version to 1.6 (requires Qt 5.12 or later)
    writer.setPdfVersion(QPdfWriter::PdfVersion_1_6);

    QPainter painter(&writer);
    painter.drawLine(100, 100, 300, 300);  // Draw a line on the first page
    painter.end();

    writer.newPage();  // Add a new page
    painter.begin(&writer);
    painter.drawText(100, 100, "This is on the second page.");
    painter.end();

    writer.close();

    return 0;
}

This example demonstrates using QPdfWriter to create a custom PDF layout. The setPageSize method sets the page size, and the setPdfVersion method (available since Qt 5.12) is used to specify PdfVersion_1_6. A QPainter object is used to draw content on the PDF pages. The newPage method adds additional pages, and the close method finalizes the PDF generation.


Third-Party PDF Libraries

  • Third-party libraries specifically designed for PDF generation
    Qt provides integration with various third-party libraries like Poppler, which offer more granular control over PDF creation features. These libraries might allow you to specify compatibility levels beyond the presets offered by PdfVersion.

QTextDocument and HTML/CSS

  • Leveraging QTextDocument with HTML and CSS
    For simpler PDF layouts with text and formatting, you can use QTextDocument in combination with HTML and CSS. This approach provides a familiar way to define the content and appearance of the PDF without requiring direct manipulation of low-level PDF elements.

Custom PDF Generation with Low-Level Classes (Advanced)

  • Directly using Qt's PDF Module (Qt Pdf)
    Qt's Qt Pdf module offers a set of low-level classes for creating and manipulating PDF documents. This approach gives you complete control over the PDF structure but requires a deeper understanding of the PDF format and requires more coding effort.

Choosing the Right Alternative

  • For complete control over PDF structure (advanced)
    Consider using Qt's Qt Pdf module directly.
  • For simple layouts with text and formatting
    Utilize QTextDocument with HTML and CSS.
  • For granular control or compatibility beyond PdfVersion
    Explore third-party libraries like Poppler.