improve: pdf export caching of jpeg bitmaps

* make cache size configurable (defaults to 15)
* have one cache object per PDFWriter instance, thus avoiding
  accidentally caching JPEGs with different compression settings

Change-Id: I6664fc09b382f471cbe7c3e7aaedb3ebb5883b47
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/93112
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>

officecfg/registry/schema/org/openoffice/Office/Common.xcs

@@ -908,6 +908,14 @@
         </info>
         <value>25</value>
       </prop>
+      <prop oor:name="PDFExportImageCacheSize" oor:type="xs:int" oor:nillable="false">
+        <info>
+           <desc>Specifies number of PDF image instances to cache on
+           export - can save potentially huge amount of CPU time on
+           re-compressing the same JPEG image over and over again.</desc>
+        </info>
+        <value>15</value>
+      </prop>
     </group>
     <group oor:name="InternalMSExport">
       <info>

vcl/source/gdi/pdfwriter_impl.cxx

@@ -41,6 +41,7 @@
 #include <cppuhelper/implbase.hxx>
 #include <i18nlangtag/languagetag.hxx>
 #include <o3tl/numeric.hxx>
+#include <officecfg/Office/Common.hxx>
 #include <osl/file.hxx>
 #include <osl/thread.h>
 #include <rtl/digest.h>
@@ -1152,6 +1153,8 @@ PDFWriterImpl::PDFWriterImpl( const PDFWriter::PDFWriterContext& rContext,
         m_nCurrentStructElement( 0 ),
         m_bEmitStructure( true ),
         m_nNextFID( 1 ),
+        m_aPDFBmpCache(
+            officecfg::Office::Common::VCL::PDFExportImageCacheSize::get() ),
         m_nCurrentPage( -1 ),
         m_nCatalogObject(0),
         m_nSignatureObject( -1 ),

vcl/source/gdi/pdfwriter_impl.hxx

@@ -46,6 +46,7 @@
 #include <vcl/wall.hxx>
 #include <o3tl/safeint.hxx>
 #include <o3tl/typed_flags_set.hxx>
+#include <o3tl/lru_map.hxx>
 #include <comphelper/hash.hxx>
 #include <tools/stream.hxx>
 
@@ -709,6 +710,10 @@ private:
     sal_Int32                           m_nNextFID;
     PDFFontCache                        m_aFontCache;
 
+    /// Cache some most recent bitmaps we've exported, in case we encounter them again..
+    o3tl::lru_map<BitmapChecksum,
+                  std::shared_ptr<SvMemoryStream>> m_aPDFBmpCache;
+
     sal_Int32                           m_nCurrentPage;
 
     sal_Int32                           m_nCatalogObject;

vcl/source/gdi/pdfwriter_impl2.cxx

@@ -43,7 +43,6 @@
 #include <com/sun/star/beans/XMaterialHolder.hpp>
 
 #include <cppuhelper/implbase.hxx>
-#include <o3tl/lru_map.hxx>
 
 #include <sal/log.hxx>
 #include <memory>
@@ -55,9 +54,6 @@ using namespace com::sun::star::beans;
 
 static bool lcl_canUsePDFAxialShading(const Gradient& rGradient);
 
-/// Cache some last 15 bitmaps we've exported, in case we encounter them again..
-static o3tl::lru_map<BitmapChecksum, std::shared_ptr<SvMemoryStream>> lcl_PDFBmpCache(15);
-
 void PDFWriterImpl::implWriteGradient( const tools::PolyPolygon& i_rPolyPoly, const Gradient& i_rGradient,
                                        VirtualDevice* i_pDummyVDev, const vcl::PDFWriter::PlayMetafileContext& i_rContext )
 {
@@ -182,9 +178,9 @@ void PDFWriterImpl::implWriteBitmapEx( const Point& i_rPoint, const Size& i_rSiz
             // from trying conversion & stores before...
             if ( !aBitmapEx.IsTransparent() )
             {
-                const auto& rCacheEntry=lcl_PDFBmpCache.find(
+                const auto& rCacheEntry=m_aPDFBmpCache.find(
                     aBitmapEx.GetChecksum());
-                if ( rCacheEntry != lcl_PDFBmpCache.end() )
+                if ( rCacheEntry != m_aPDFBmpCache.end() )
                 {
                     m_rOuterFace.DrawJPGBitmap( *rCacheEntry->second, true, aSizePixel,
                                                 tools::Rectangle( aPoint, aSize ), aMask, i_Graphic );
@@ -266,7 +262,7 @@ void PDFWriterImpl::implWriteBitmapEx( const Point& i_rPoint, const Size& i_rSiz
             if (!aBitmapEx.IsTransparent() && bTrueColorJPG)
             {
                 // Cache last jpeg export
-                lcl_PDFBmpCache.insert(
+                m_aPDFBmpCache.insert(
                     {aBitmapEx.GetChecksum(), pStrm});
             }
         }