pdf export: be a bit less wasteful when jpeg-optimising bitmaps

Before, code was test-compressing every single bitmap coming along.
Let's buffer those SvMemStreams, and keep the last 15 around in
case the same image comes along again.

Change-Id: Ic8da32725ea46b01bd6beacc389abf8f52845d36
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/93058
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>

1 files changed, 30 insertions, 6 deletions

diff --git a/vcl/source/gdi/pdfwriter_impl2.cxx b/vcl/source/gdi/pdfwriter_impl2.cxx
index f08067f356f5..f84ab684c24c 100644
--- a/vcl/source/gdi/pdfwriter_impl2.cxx
+++ b/vcl/source/gdi/pdfwriter_impl2.cxx
@@ -43,6 +43,7 @@
 #include <com/sun/star/beans/XMaterialHolder.hpp>
 
 #include <cppuhelper/implbase.hxx>
+#include <o3tl/lru_map.hxx>
 
 #include <sal/log.hxx>
 #include <memory>
@@ -54,6 +55,9 @@ 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 )
 {
@@ -168,13 +172,25 @@ void PDFWriterImpl::implWriteBitmapEx( const Point& i_rPoint, const Size& i_rSiz
         if ( bIsPng || ( aSizePixel.Width() < 32 ) || ( aSizePixel.Height() < 32 ) )
             bUseJPGCompression = false;
 
-        SvMemoryStream  aStrm;
-        Bitmap          aMask;
+        auto   pStrm=std::make_shared<SvMemoryStream>();
+        Bitmap aMask;
 
         bool bTrueColorJPG = true;
         if ( bUseJPGCompression )
         {
-
+            // TODO this checks could be done much earlier, saving us
+            // from trying conversion & stores before...
+            if ( !aBitmapEx.IsTransparent() )
+            {
+                const auto& rCacheEntry=lcl_PDFBmpCache.find(
+                    aBitmapEx.GetChecksum());
+                if ( rCacheEntry != lcl_PDFBmpCache.end() )
+                {
+                    m_rOuterFace.DrawJPGBitmap( *rCacheEntry->second, true, aSizePixel,
+                                                tools::Rectangle( aPoint, aSize ), aMask, i_Graphic );
+                    return;
+                }
+            }
             sal_uInt32 nZippedFileSize = 0; // sj: we will calculate the filesize of a zipped bitmap
             if ( !bIsJpeg )                 // to determine if jpeg compression is useful
             {
@@ -201,7 +217,7 @@ void PDFWriterImpl::implWriteBitmapEx( const Point& i_rPoint, const Size& i_rSiz
 
             try
             {
-                uno::Reference < io::XStream > xStream = new utl::OStreamWrapper( aStrm );
+                uno::Reference < io::XStream > xStream = new utl::OStreamWrapper( *pStrm );
                 uno::Reference< io::XSeekable > xSeekable( xStream, UNO_QUERY_THROW );
                 uno::Reference< uno::XComponentContext > xContext( comphelper::getProcessComponentContext() );
                 uno::Reference< graphic::XGraphicProvider > xGraphicProvider( graphic::GraphicProvider::create(xContext) );
@@ -222,7 +238,7 @@ void PDFWriterImpl::implWriteBitmapEx( const Point& i_rPoint, const Size& i_rSiz
                 }
                 else
                 {
-                    aStrm.Seek( STREAM_SEEK_TO_END );
+                    pStrm->Seek( STREAM_SEEK_TO_END );
 
                     xSeekable->seek( 0 );
                     Sequence< PropertyValue > aArgs( 1 );
@@ -245,7 +261,15 @@ void PDFWriterImpl::implWriteBitmapEx( const Point& i_rPoint, const Size& i_rSiz
             }
         }
         if ( bUseJPGCompression )
-            m_rOuterFace.DrawJPGBitmap( aStrm, bTrueColorJPG, aSizePixel, tools::Rectangle( aPoint, aSize ), aMask, i_Graphic );
+        {
+            m_rOuterFace.DrawJPGBitmap( *pStrm, bTrueColorJPG, aSizePixel, tools::Rectangle( aPoint, aSize ), aMask, i_Graphic );
+            if (!aBitmapEx.IsTransparent() && bTrueColorJPG)
+            {
+                // Cache last jpeg export
+                lcl_PDFBmpCache.insert(
+                    {aBitmapEx.GetChecksum(), pStrm});
+            }
+        }
         else if ( aBitmapEx.IsTransparent() )
             m_rOuterFace.DrawBitmapEx( aPoint, aSize, aBitmapEx );
         else