PDF writer: implement support for document internal links

QPdfEngine already supported links to external URIs, but not internal
links for navigation in a document.

For internal links, PDF supports "named destinations" instead of
direct coordinates. That way, we avoid the need for a two-pass
implementation. Instead, we just store the name and position of all
anchors as we enounter them. At document finishing time, we export the
list of named destinations in a PDF "name tree" structure.

The PDF named destinations feature uses the same main catalog item
("Names") as the attached files feature. Hence, this commit must
slightly change the implementation of file attachment support also, so
that the structure supports both. Now, we always add a reference to a
Names object in the catalog when we start the document. When we
finish, we write that object, making it reference the attached
files-structure and/or the named destinations-structure, as needed.

Fixes: QTBUG-83458
Change-Id: I9c43e7b423062d3f21965ab8a0d81a53c4dd72cb
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 12 insertions, 1 deletions

diff --git a/src/gui/painting/qpdf_p.h b/src/gui/painting/qpdf_p.h
index 4c6a570e76..2c70ddf664 100644
--- a/src/gui/painting/qpdf_p.h
+++ b/src/gui/painting/qpdf_p.h
@@ -271,7 +271,9 @@ private:
     int writeXmpDcumentMetaData();
     int writeOutputIntent();
     void writePageRoot();
+    void writeDestsRoot();
     void writeAttachmentRoot();
+    void writeNamesRoot();
     void writeFonts();
     void embedFont(QFontSubset *font);
     qreal calcUserUnit() const;
@@ -305,11 +307,20 @@ private:
         QString mimeType;
     };
 
+    struct DestInfo
+    {
+        QString anchor;
+        uint pageObj;
+        QPointF coords;
+    };
+
     // various PDF objects
-    int pageRoot, embeddedfilesRoot, namesRoot, catalog, info, graphicsState, patternColorSpace;
+    int pageRoot, namesRoot, destsRoot, attachmentsRoot, catalog, info;
+    int graphicsState, patternColorSpace;
     QList<uint> pages;
     QHash<qint64, uint> imageCache;
     QHash<QPair<uint, uint>, uint > alphaCache;
+    QList<DestInfo> destCache;
     QList<AttachmentInfo> fileCache;
     QByteArray xmpDocumentMetadata;
 };