tdf#118535 DOCX export: save header image once

Writer used to dump the same image file as many times
as it was featured in different headers or footers in
the document, bloating the .docx file size.

This is countered by making all "relationships" in the
header*.xml.rels files point to the same image.

Change-Id: I44d72630289c721d58d8f7e208517df2f1fe621c
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/112656
Tested-by: László Németh <nemeth@numbertext.org>
Reviewed-by: László Németh <nemeth@numbertext.org>

2 files changed, 28 insertions, 13 deletions

diff --git a/oox/source/export/drawingml.cxx b/oox/source/export/drawingml.cxx
index 67f26e71daea..32780296ce89 100644
--- a/oox/source/export/drawingml.cxx
+++ b/oox/source/export/drawingml.cxx
@@ -1162,7 +1162,7 @@ const char* DrawingML::GetRelationCompPrefix() const
     return "unknown";
 }
 
-OUString DrawingML::WriteImage( const Graphic& rGraphic , bool bRelPathToMedia )
+OUString DrawingML::WriteImage( const Graphic& rGraphic , bool bRelPathToMedia, OUString* pFileName )
 {
     GfxLink aLink = rGraphic.GetGfxLink ();
     OUString sMediaType;
@@ -1266,15 +1266,18 @@ OUString DrawingML::WriteImage( const Graphic& rGraphic , bool bRelPathToMedia )
         sRelationCompPrefix = "../";
     else
         sRelationCompPrefix = GetRelationCompPrefix();
+    OUString sPath = OUStringBuffer()
+                     .appendAscii( sRelationCompPrefix.getStr() )
+                     .appendAscii( sRelPathToMedia.getStr() )
+                     .append( static_cast<sal_Int32>(mnImageCounter ++) )
+                     .appendAscii( pExtension )
+                     .makeStringAndClear();
     sRelId = mpFB->addRelation( mpFS->getOutputStream(),
                                 oox::getRelationship(Relationship::IMAGE),
-                                OUStringBuffer()
-                                .appendAscii( sRelationCompPrefix.getStr() )
-                                .appendAscii( sRelPathToMedia.getStr() )
-                                .append( static_cast<sal_Int32>(mnImageCounter ++) )
-                                .appendAscii( pExtension )
-                                .makeStringAndClear() );
+                                sPath );
 
+    if (pFileName)
+        *pFileName = sPath;
     return sRelId;
 }
 
@@ -1434,6 +1437,7 @@ OUString DrawingML::WriteXGraphicBlip(uno::Reference<beans::XPropertySet> const
                                       bool bRelPathToMedia)
 {
     OUString sRelId;
+    OUString sFileName;
 
     if (!rxGraphic.is())
         return sRelId;
@@ -1443,16 +1447,25 @@ OUString DrawingML::WriteXGraphicBlip(uno::Reference<beans::XPropertySet> const
     {
         BitmapChecksum nChecksum = aGraphic.GetChecksum();
         sRelId = mpTextExport->FindRelId(nChecksum);
+        sFileName = mpTextExport->FindFileName(nChecksum);
     }
     if (sRelId.isEmpty())
     {
-        sRelId = WriteImage(aGraphic, bRelPathToMedia);
+        sRelId = WriteImage(aGraphic, bRelPathToMedia, &sFileName);
         if (mpTextExport)
         {
             BitmapChecksum nChecksum = aGraphic.GetChecksum();
-            mpTextExport->CacheRelId(nChecksum, sRelId);
+            mpTextExport->CacheRelId(nChecksum, sRelId, sFileName);
         }
     }
+    else
+    {
+        // Include the same relation again. This makes it possible to
+        // reuse an image across different headers.
+        sRelId = mpFB->addRelation( mpFS->getOutputStream(),
+                                    oox::getRelationship(Relationship::IMAGE),
+                                    sFileName );
+    }
 
     mpFS->startElementNS(XML_a, XML_blip, FSNS(XML_r, XML_embed), sRelId);
 
diff --git a/oox/source/export/vmlexport.cxx b/oox/source/export/vmlexport.cxx
index 9c6b89ef7dd7..9f8df2279611 100644
--- a/oox/source/export/vmlexport.cxx
+++ b/oox/source/export/vmlexport.cxx
@@ -741,8 +741,9 @@ void VMLExport::Commit( EscherPropertyContainer& rProps, const tools::Rectangle&
                         OUString aImageId = m_pTextExport->FindRelId(nChecksum);
                         if (aImageId.isEmpty())
                         {
-                            aImageId = m_pTextExport->GetDrawingML().WriteImage(aGraphic);
-                            m_pTextExport->CacheRelId(nChecksum, aImageId);
+                            OUString aFileName;
+                            aImageId = m_pTextExport->GetDrawingML().WriteImage(aGraphic, false, &aFileName);
+                            m_pTextExport->CacheRelId(nChecksum, aImageId, aFileName);
                         }
                         pAttrList->add(FSNS(XML_r, XML_id),
                                        OUStringToOString(aImageId, RTL_TEXTENCODING_UTF8));
@@ -763,8 +764,9 @@ void VMLExport::Commit( EscherPropertyContainer& rProps, const tools::Rectangle&
                         OUString aImageId = m_pTextExport->FindRelId(nChecksum);
                         if (aImageId.isEmpty())
                         {
-                            aImageId = m_pTextExport->GetDrawingML().WriteImage(aGraphic);
-                            m_pTextExport->CacheRelId(nChecksum, aImageId);
+                            OUString aFileName;
+                            aImageId = m_pTextExport->GetDrawingML().WriteImage(aGraphic, false, &aFileName);
+                            m_pTextExport->CacheRelId(nChecksum, aImageId, aFileName);
                         }
                         pAttrList->add(FSNS(XML_r, XML_id),
                                        OUStringToOString(aImageId, RTL_TEXTENCODING_UTF8));