PDF: add support for PDF/X-4

PDF/X-4 is a subset of PDF 1.6, aimed at printing fidelity. We can
support it with a few refactorings of the existing code in
QPdfEngine.

* Add the new PDF version to QPagedPaintDevice / QPdfEngine.

* Always write the XMP metadata, no matter what's the PDF version
  used. XMP used to be written only for PDF/A-1b, but it's supported
  by PDF 1.4 and 1.6 so there's little reason not to write it.

* While at it, ditch the search&replace approach for the metadata
  and use QXmlStreamWriter instead, since it gives us extra
  flexibility that we need (emit different tags depending on the
  PDF version in use).

* The old code had a bug where the timestamps in the XMP metadata
  and the document information dictionary could fall out of sync.
  Just use one datetime object in both places.

* Add /ModDate and xmp:ModifyDate (required).

* Add the required attributes in the xmpMM namespace.

* Add a way to set the document ID to a custom UUID, and use it
  in the XMP metadata as well as in the /ID in the trailer. Emit
  the ID unconditionally, as it's been available since PDF 1.1.

* Emit the output intent for both PDF/A-1b and /X-4. This will be
  amended in a future commit to let the user choose the colorspace.

The only missing bit is §6.5.4 of the PDF/X-4 spec. This imposes that
all symbolic TrueType fonts shall *not* specify an Encoding, and have
exactly one encoding in the cmap table. This is basically requiring what
§5.5.5 in PDF 1.6 only suggests (page 400). However it seems that we are
not embedding a cmap table when extracting a font subset, and that's
already violating PDF/A-1b anyhow. This is tracked by QTBUG-125405.

This work has been kindly sponsored by the QGIS project
(https://qgis.org/).

[ChangeLog][QtGui][QPdfWriter] Support for PDF/X-4 has been
added.

Task-number: QTBUG-125405
Change-Id: Ia81f29b07b819eca5767c9f17692d92a3010f5ad
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit 2fbece8a73cb2d2692c78c38e1576c0c9c62fce7)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/CMakeLists.txt

@@ -309,7 +309,6 @@ if(QT_FEATURE_pdf)
     )
     set(qpdf_resource_files
         "../3rdparty/icc/sRGB2014.icc"
-        "painting/qpdfa_metadata.xml"
     )
     qt_internal_extend_target(Gui
         ATTRIBUTION_FILE_DIR_PATHS

src/gui/painting/qpagedpaintdevice.cpp

@@ -67,6 +67,9 @@ QPagedPaintDevicePrivate *QPagedPaintDevice::dd()
 
     \value PdfVersion_1_6 A PDF 1.6 compatible document is produced.
            This value was added in Qt 5.12.
+
+    \value [since 6.8] PdfVersion_X4 A PDF/X-4 compatible document is
+           produced.
 */
 
 /*!

src/gui/painting/qpagedpaintdevice.h

@@ -25,7 +25,12 @@ public:
     virtual bool newPage() = 0;
 
     // keep in sync with QPdfEngine::PdfVersion!
-    enum PdfVersion { PdfVersion_1_4, PdfVersion_A1b, PdfVersion_1_6 };
+    enum PdfVersion {
+        PdfVersion_1_4,
+        PdfVersion_A1b,
+        PdfVersion_1_6,
+        PdfVersion_X4,
+    };
 
     virtual bool setPageLayout(const QPageLayout &pageLayout);
     virtual bool setPageSize(const QPageSize &pageSize);

src/gui/painting/qpdf.cpp

@@ -22,6 +22,7 @@
 #include <qtemporaryfile.h>
 #include <qtimezone.h>
 #include <quuid.h>
+#include <qxmlstream.h>
 
 #include <map>
 
@@ -1043,6 +1044,12 @@ void QPdfEngine::drawHyperlink(const QRectF &r, const QUrl &url)
 {
     Q_D(QPdfEngine);
 
+    // PDF/X-4 (§ 6.17) does not allow annotations that don't lie
+    // outside the BleedBox/TrimBox, so don't emit an hyperlink
+    // annotation at all.
+    if (d->pdfVersion == QPdfEngine::Version_X4)
+        return;
+
     const uint annot = d->addXrefEntry(-1);
     const QByteArray urlascii = url.toEncoded();
     int len = urlascii.size();
@@ -1556,6 +1563,7 @@ void QPdfEnginePrivate::writeHeader()
         "1.4", // Version_1_4
         "1.4", // Version_A1b
         "1.6", // Version_1_6
+        "1.6", // Version_X4
     };
     static const size_t numMappings = sizeof mapping / sizeof *mapping;
     const char *verStr = mapping[size_t(pdfVersion) < numMappings ? pdfVersion : 0];
@@ -1563,17 +1571,28 @@ void QPdfEnginePrivate::writeHeader()
     xprintf("%%PDF-%s\n", verStr);
     xprintf("%%\303\242\303\243\n");
 
-    writeInfo();
+#if QT_CONFIG(timezone)
+    const QDateTime now = QDateTime::currentDateTime(QTimeZone::systemTimeZone());
+#else
+    const QDateTime now = QDateTime::currentDateTimeUtc();
+#endif
 
-    int metaDataObj = -1;
+    writeInfo(now);
-    int outputIntentObj = -1;
+
-    if (pdfVersion == QPdfEngine::Version_A1b || !xmpDocumentMetadata.isEmpty()) {
+    const int metaDataObj = writeXmpDocumentMetaData(now);
-        metaDataObj = writeXmpDocumentMetaData();
+    const int outputIntentObj = [&]() {
-    }
+        switch (pdfVersion) {
-    if (pdfVersion == QPdfEngine::Version_A1b) {
+        case QPdfEngine::Version_1_4:
-        outputIntentObj = writeOutputIntent();
+        case QPdfEngine::Version_1_6:
+            break;
+        case QPdfEngine::Version_A1b:
+        case QPdfEngine::Version_X4:
+            return writeOutputIntent();
         }
 
+        return -1;
+    }();
+
     catalog = addXrefEntry(-1);
     pageRoot = requestObject();
     namesRoot = requestObject();
@@ -1587,10 +1606,9 @@ void QPdfEnginePrivate::writeHeader()
           << "/Pages " << pageRoot << "0 R\n"
           << "/Names " << namesRoot << "0 R\n";
 
-        if (pdfVersion == QPdfEngine::Version_A1b || !xmpDocumentMetadata.isEmpty())
         s << "/Metadata " << metaDataObj << "0 R\n";
 
-        if (pdfVersion == QPdfEngine::Version_A1b)
+        if (outputIntentObj >= 0)
             s << "/OutputIntents [" << outputIntentObj << "0 R]\n";
 
         s << ">>\n"
@@ -1716,64 +1734,171 @@ void QPdfEnginePrivate::writeColor(ColorDomain domain, const QColor &color)
     }
 }
 
-void QPdfEnginePrivate::writeInfo()
+void QPdfEnginePrivate::writeInfo(const QDateTime &date)
 {
     info = addXrefEntry(-1);
-    xprintf("<<\n/Title ");
+    write("<<\n/Title ");
     printString(title);
-    xprintf("\n/Creator ");
+    write("\n/Creator ");
     printString(creator);
-    xprintf("\n/Producer ");
+    write("\n/Producer ");
     printString(QString::fromLatin1("Qt " QT_VERSION_STR));
-    QDateTime now = QDateTime::currentDateTime();
+
-    QTime t = now.time();
+    const QTime t = date.time();
-    QDate d = now.date();
+    const QDate d = date.date();
-    xprintf("\n/CreationDate (D:%d%02d%02d%02d%02d%02d",
+    // (D:YYYYMMDDHHmmSSOHH'mm')
-            d.year(),
+    constexpr size_t formattedDateSize = 26;
+    char formattedDate[formattedDateSize];
+    const int year = qBound(0, d.year(), 9999); // ASN.1, max 4 digits
+    auto printedSize = qsnprintf(formattedDate,
+                                 formattedDateSize,
+                                 "(D:%04d%02d%02d%02d%02d%02d",
+                                 year,
                                  d.month(),
                                  d.day(),
                                  t.hour(),
                                  t.minute(),
                                  t.second());
-    int offset = now.offsetFromUtc();
+    const int offset = date.offsetFromUtc();
-    int hours  = (offset / 60) / 60;
+    const int hours  = (offset / 60) / 60;
-    int mins   = (offset / 60) % 60;
+    const int mins   = (offset / 60) % 60;
-    if (offset < 0)
+    if (offset < 0) {
-        xprintf("-%02d'%02d')\n", -hours, -mins);
+        qsnprintf(formattedDate + printedSize,
-    else if (offset > 0)
+                  formattedDateSize - printedSize,
-        xprintf("+%02d'%02d')\n", hours , mins);
+                  "-%02d'%02d')", -hours, -mins);
-    else
+    } else if (offset > 0) {
-        xprintf("Z)\n");
+        qsnprintf(formattedDate + printedSize,
-    xprintf("/Trapped /False\n");
+                  formattedDateSize - printedSize,
-    xprintf(">>\n"
+                  "+%02d'%02d')", hours, mins);
+    } else {
+        qsnprintf(formattedDate + printedSize,
+                  formattedDateSize - printedSize,
+                  "Z)");
+    }
+
+    write("\n/CreationDate ");
+    write(formattedDate);
+    write("\n/ModDate ");
+    write(formattedDate);
+
+    write("\n/Trapped /False\n"
+          "2\n"
           "endobj\n");
 }
 
-int QPdfEnginePrivate::writeXmpDocumentMetaData()
+int QPdfEnginePrivate::writeXmpDocumentMetaData(const QDateTime &date)
 {
     const int metaDataObj = addXrefEntry(-1);
     QByteArray metaDataContent;
 
-    if (xmpDocumentMetadata.isEmpty()) {
+    if (!xmpDocumentMetadata.isEmpty()) {
-        const QString producer(QString::fromLatin1("Qt " QT_VERSION_STR));
-
-#if QT_CONFIG(timezone)
-        const QDateTime now = QDateTime::currentDateTime(QTimeZone::systemTimeZone());
-#else
-        const QDateTime now = QDateTime::currentDateTimeUtc();
-#endif
-        const QString metaDataDate = now.toString(Qt::ISODate);
-
-        QFile metaDataFile(":/qpdf/qpdfa_metadata.xml"_L1);
-        bool ok = metaDataFile.open(QIODevice::ReadOnly);
-        Q_ASSERT(ok);
-        metaDataContent = QString::fromUtf8(metaDataFile.readAll()).arg(producer.toHtmlEscaped(),
-                                                                        title.toHtmlEscaped(),
-                                                                        creator.toHtmlEscaped(),
-                                                                        metaDataDate).toUtf8();
-    }
-    else
         metaDataContent = xmpDocumentMetadata;
+    } else {
+        const QString producer(QString::fromLatin1("Qt " QT_VERSION_STR));
+        const QString metaDataDate = date.toString(Qt::ISODate);
+
+        using namespace Qt::Literals;
+        constexpr QLatin1String xmlNS = "http://www.w3.org/XML/1998/namespace"_L1;
+
+        constexpr QLatin1String adobeNS = "adobe:ns:meta/"_L1;
+        constexpr QLatin1String rdfNS = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"_L1;
+        constexpr QLatin1String dcNS = "http://purl.org/dc/elements/1.1/"_L1;
+        constexpr QLatin1String xmpNS = "http://ns.adobe.com/xap/1.0/"_L1;
+        constexpr QLatin1String xmpMMNS = "http://ns.adobe.com/xap/1.0/mm/"_L1;
+        constexpr QLatin1String pdfNS = "http://ns.adobe.com/pdf/1.3/"_L1;
+        constexpr QLatin1String pdfaidNS = "http://www.aiim.org/pdfa/ns/id/"_L1;
+        constexpr QLatin1String pdfxidNS = "http://www.npes.org/pdfx/ns/id/"_L1;
+
+        QBuffer output(&metaDataContent);
+        output.open(QIODevice::WriteOnly);
+        output.write("<?xpacket begin='' id='W5M0MpCehiHzreSzNTczkc9d'?>");
+
+        QXmlStreamWriter w(&output);
+        w.setAutoFormatting(true);
+        w.writeNamespace(adobeNS, "x");
+        w.writeNamespace(rdfNS, "rdf");
+        w.writeNamespace(dcNS, "dc");
+        w.writeNamespace(xmpNS, "xmp");
+        w.writeNamespace(xmpMMNS, "xmpMM");
+        w.writeNamespace(pdfNS, "pdf");
+        w.writeNamespace(pdfaidNS, "pdfaid");
+        w.writeNamespace(pdfxidNS, "pdfxid");
+
+        w.writeStartElement(adobeNS, "xmpmeta");
+        w.writeStartElement(rdfNS, "RDF");
+
+        /*
+            XMP says: "The recommended approach is to have either a
+            single rdf:Description element containing all XMP
+            properties or a separate rdf:Description element for each
+            XMP property namespace."
+            We do the the latter.
+        */
+
+        // DC
+        w.writeStartElement(rdfNS, "Description");
+        w.writeAttribute(rdfNS, "about", "");
+            w.writeStartElement(dcNS, "title");
+                w.writeStartElement(rdfNS, "Alt");
+                    w.writeStartElement(rdfNS, "li");
+                    w.writeAttribute(xmlNS, "lang", "x-default");
+                        w.writeCharacters(title);
+                    w.writeEndElement();
+                w.writeEndElement();
+            w.writeEndElement();
+        w.writeEndElement();
+
+        // PDF
+        w.writeStartElement(rdfNS, "Description");
+        w.writeAttribute(rdfNS, "about", "");
+        w.writeAttribute(pdfNS, "Producer", producer);
+        w.writeAttribute(pdfNS, "Trapped", "false");
+        w.writeEndElement();
+
+        // XMP
+        w.writeStartElement(rdfNS, "Description");
+        w.writeAttribute(rdfNS, "about", "");
+        w.writeAttribute(xmpNS, "CreatorTool", creator);
+        w.writeAttribute(xmpNS, "CreateDate", metaDataDate);
+        w.writeAttribute(xmpNS, "ModifyDate", metaDataDate);
+        w.writeAttribute(xmpNS, "MetadataDate", metaDataDate);
+        w.writeEndElement();
+
+        // XMPMM
+        w.writeStartElement(rdfNS, "Description");
+        w.writeAttribute(rdfNS, "about", "");
+        w.writeAttribute(xmpMMNS, "DocumentID", "uuid:"_L1 + documentId.toString(QUuid::WithoutBraces));
+        w.writeAttribute(xmpMMNS, "VersionID", "1");
+        w.writeAttribute(xmpMMNS, "RenditionClass", "default");
+        w.writeEndElement();
+
+        // Version-specific
+        switch (pdfVersion) {
+        case QPdfEngine::Version_1_4:
+            break;
+        case QPdfEngine::Version_A1b:
+            w.writeStartElement(rdfNS, "Description");
+            w.writeAttribute(rdfNS, "about", "");
+            w.writeAttribute(pdfaidNS, "part", "1");
+            w.writeAttribute(pdfaidNS, "conformance", "B");
+            w.writeEndElement();
+            break;
+        case QPdfEngine::Version_1_6:
+            break;
+        case QPdfEngine::Version_X4:
+            w.writeStartElement(rdfNS, "Description");
+            w.writeAttribute(rdfNS, "about", "");
+            w.writeAttribute(pdfxidNS, "GTS_PDFXVersion", "PDF/X-4");
+            w.writeEndElement();
+            break;
+        }
+
+        w.writeEndElement(); // </RDF>
+        w.writeEndElement(); // </xmpmeta>
+
+        w.writeEndDocument();
+        output.write("<?xpacket end='w'?>");
+    }
 
     xprintf("<<\n"
             "/Type /Metadata /Subtype /XML\n"
@@ -1821,7 +1946,20 @@ int QPdfEnginePrivate::writeOutputIntent()
     {
         xprintf("<<\n");
         xprintf("/Type /OutputIntent\n");
+
+        switch (pdfVersion) {
+        case QPdfEngine::Version_1_4:
+        case QPdfEngine::Version_1_6:
+            Q_UNREACHABLE(); // no output intent for these versions
+            break;
+        case QPdfEngine::Version_A1b:
             xprintf("/S/GTS_PDFA1\n");
+            break;
+        case QPdfEngine::Version_X4:
+            xprintf("/S/GTS_PDFX\n");
+            break;
+        }
+
         xprintf("/OutputConditionIdentifier (sRGB_IEC61966-2-1_black_scaled)\n");
         xprintf("/DestOutputProfile %d 0 R\n", colorProfile);
         xprintf("/Info(sRGB IEC61966 v2.1 with black scaling)\n");
@@ -2242,11 +2380,8 @@ void QPdfEnginePrivate::writeTail()
           << "/Info " << info << "0 R\n"
           << "/Root " << catalog << "0 R\n";
 
-        if (pdfVersion == QPdfEngine::Version_A1b) {
+        const QByteArray id = documentId.toString(QUuid::WithoutBraces).toUtf8().toHex();
-            const QString uniqueId = QUuid::createUuid().toString();
+        s << "/ID [ <" << id << "> <" << id << "> ]\n";
-            const QByteArray fileIdentifier = QCryptographicHash::hash(uniqueId.toLatin1(), QCryptographicHash::Md5).toHex();
-            s << "/ID [ <" << fileIdentifier << "> <" << fileIdentifier << "> ]\n";
-        }
 
         s << ">>\n"
           << "startxref\n" << xrefPositions.constLast() << "\n"
@@ -3198,7 +3333,11 @@ void QPdfEnginePrivate::drawTextItem(const QPointF &p, const QTextItemInt &ti)
 
     const bool isLink = ti.charFormat.hasProperty(QTextFormat::AnchorHref);
     const bool isAnchor = ti.charFormat.hasProperty(QTextFormat::AnchorName);
-    if (isLink || isAnchor) {
+    // PDF/X-4 (§ 6.17) does not allow annotations that don't lie
+    // outside the BleedBox/TrimBox, so don't emit an hyperlink
+    // annotation at all.
+    const bool isX4 = pdfVersion == QPdfEngine::Version_X4;
+    if ((isLink && !isX4) || isAnchor) {
         qreal size = ti.fontEngine->fontDef.pixelSize;
         int synthesized = ti.fontEngine->synthesized();
         qreal stretch = synthesized & QFontEngine::SynthesizedStretch ? ti.fontEngine->fontDef.stretch/100. : 1.;

src/gui/painting/qpdf_p.h

@@ -21,6 +21,7 @@
 
 #include "QtCore/qlist.h"
 #include "QtCore/qstring.h"
+#include "QtCore/quuid.h"
 #include "private/qfontengine_p.h"
 #include "private/qfontsubset_p.h"
 #include "private/qpaintengine_p.h"
@@ -134,7 +135,8 @@ public:
     {
         Version_1_4,
         Version_A1b,
-        Version_1_6
+        Version_1_6,
+        Version_X4,
     };
 
     QPdfEngine();
@@ -262,6 +264,7 @@ public:
     QString outputFileName;
     QString title;
     QString creator;
+    QUuid documentId = QUuid::createUuid();
     bool embedFonts;
     int resolution;
 
@@ -289,8 +292,8 @@ private:
 
     QPdfEngine::ColorModel colorModelForColor(const QColor &color) const;
     void writeColor(ColorDomain domain, const QColor &color);
-    void writeInfo();
+    void writeInfo(const QDateTime &date);
-    int writeXmpDocumentMetaData();
+    int writeXmpDocumentMetaData(const QDateTime &date);
     int writeOutputIntent();
     void writePageRoot();
     void writeDestsRoot();

src/gui/painting/qpdfa_metadata.xml

@@ -1,16 +0,0 @@
-<?xpacket begin='' id='W5M0MpCehiHzreSzNTczkc9d'?>
-<x:xmpmeta xmlns:x="adobe:ns:meta/">
-  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
-    <rdf:Description xmlns:dc="http://purl.org/dc/elements/1.1/" rdf:about="">
-      <dc:title>
-        <rdf:Alt>
-          <rdf:li xml:lang="x-default">%2</rdf:li>
-        </rdf:Alt>
-      </dc:title>
-    </rdf:Description>
-    <rdf:Description xmlns:xmp="http://ns.adobe.com/xap/1.0/" rdf:about="" xmp:CreatorTool="%3" xmp:CreateDate="%4" xmp:ModifyDate="%4"/>
-    <rdf:Description xmlns:pdf="http://ns.adobe.com/pdf/1.3/" rdf:about="" pdf:Producer="%1"/>
-    <rdf:Description xmlns:pdfaid="http://www.aiim.org/pdfa/ns/id/" rdf:about="" pdfaid:part="1" pdfaid:conformance="B"/>
-  </rdf:RDF>
-</x:xmpmeta>
-<?xpacket end='w'?>

src/gui/painting/qpdfwriter.cpp

@@ -188,6 +188,27 @@ void QPdfWriter::setCreator(const QString &creator)
     d->engine->d_func()->creator = creator;
 }
 
+/*!
+  \since 6.8
+  Returns the ID of the document. By default, the ID is a
+  randomly generated UUID.
+  */
+QUuid QPdfWriter::documentId() const
+{
+    Q_D(const QPdfWriter);
+    return d->engine->d_func()->documentId;
+}
+
+/*!
+  \since 6.8
+  Sets the ID of the document to \a documentId.
+  */
+void QPdfWriter::setDocumentId(const QUuid &documentId)
+{
+    Q_D(QPdfWriter);
+    d->engine->d_func()->documentId = documentId;
+}
+
 /*!
   \reimp
   */

src/gui/painting/qpdfwriter.h

@@ -16,6 +16,7 @@ QT_BEGIN_NAMESPACE
 
 class QIODevice;
 class QPdfWriterPrivate;
+class QUuid;
 
 class Q_GUI_EXPORT QPdfWriter : public QObject, public QPagedPaintDevice
 {
@@ -34,6 +35,9 @@ public:
     QString creator() const;
     void setCreator(const QString &creator);
 
+    QUuid documentId() const;
+    void setDocumentId(const QUuid &documentId);
+
     bool newPage() override;
 
     void setResolution(int resolution);

tests/auto/printsupport/kernel/qprinter/tst_qprinter.cpp

@@ -548,9 +548,13 @@ void tst_QPrinter::taskQTBUG4497_reusePrinterOnDifferentFiles()
         QByteArray file1Line = file1.readLine();
         QByteArray file2Line = file2.readLine();
 
-        if (!file1Line.contains("CreationDate"))
+        if (!file1Line.startsWith("/CreationDate ") &&
+            !file1Line.startsWith("/ModDate ") &&
+            !file1Line.startsWith("/ID "))
+        {
             QCOMPARE(file1Line, file2Line);
         }
+    }
 
     QVERIFY(file1.atEnd());
     QVERIFY(file2.atEnd());