PDF export: skip pointless downsampling for very small images

Regression from commit b6588bd7c831ce88a29131ca7ea8d3f3e082564e (Reduce
image resolution by default in PDF Export, 2014-03-02) the problem is
that in case you have small enough bitmaps, then these used to look
OK at reasonable zoom levels, but now we intentionally scale down
bitmaps by default.

That makes little sense for tiny images, do this only for large ones.

Change-Id: Iff15325b842b47d9285a7c0f83f402897498392d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/87086
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins

3 files changed, 66 insertions, 2 deletions

diff --git a/vcl/qa/cppunit/pdfexport/data/reduce-small-image.fodt b/vcl/qa/cppunit/pdfexport/data/reduce-small-image.fodt
new file mode 100644
index 000000000000..99ff22746e48
--- /dev/null
+++ b/vcl/qa/cppunit/pdfexport/data/reduce-small-image.fodt
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<office:document xmlns:grddl="http://www.w3.org/2003/g/data-view#" xmlns:xhtml="http://www.w3.org/1999/xhtml" xmlns:css3t="http://www.w3.org/TR/css3-text/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:formx="urn:openoffice:names:experimental:ooxml-odf-interop:xmlns:form:1.0" xmlns:xforms="http://www.w3.org/2002/xforms" xmlns:dom="http://www.w3.org/2001/xml-events" xmlns:script="urn:oasis:names:tc:opendocument:xmlns:script:1.0" xmlns:form="urn:oasis:names:tc:opendocument:xmlns:form:1.0" xmlns:math="http://www.w3.org/1998/Math/MathML" xmlns:field="urn:openoffice:names:experimental:ooo-ms-interop:xmlns:field:1.0" xmlns:of="urn:oasis:names:tc:opendocument:xmlns:of:1.2" xmlns:oooc="http://openoffice.org/2004/calc" xmlns:ooow="http://openoffice.org/2004/writer" xmlns:config="urn:oasis:names:tc:opendocument:xmlns:config:1.0" xmlns:tableooo="http://openoffice.org/2009/table" xmlns:text="urn:oasis:names:tc:opendocument:xmlns:text:1.0" xmlns:calcext="urn:org:documentfoundation:names:experimental:calc:xmlns:calcext:1.0" xmlns:fo="urn:oasis:names:tc:opendocument:xmlns:xsl-fo-compatible:1.0" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:office="urn:oasis:names:tc:opendocument:xmlns:office:1.0" xmlns:loext="urn:org:documentfoundation:names:experimental:office:xmlns:loext:1.0" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ooo="http://openoffice.org/2004/office" xmlns:table="urn:oasis:names:tc:opendocument:xmlns:table:1.0" xmlns:meta="urn:oasis:names:tc:opendocument:xmlns:meta:1.0" xmlns:officeooo="http://openoffice.org/2009/office" xmlns:style="urn:oasis:names:tc:opendocument:xmlns:style:1.0" xmlns:drawooo="http://openoffice.org/2010/draw" xmlns:draw="urn:oasis:names:tc:opendocument:xmlns:drawing:1.0" xmlns:dr3d="urn:oasis:names:tc:opendocument:xmlns:dr3d:1.0" xmlns:svg="urn:oasis:names:tc:opendocument:xmlns:svg-compatible:1.0" xmlns:chart="urn:oasis:names:tc:opendocument:xmlns:chart:1.0" xmlns:rpt="http://openoffice.org/2005/report" xmlns:number="urn:oasis:names:tc:opendocument:xmlns:datastyle:1.0" office:version="1.2" office:mimetype="application/vnd.oasis.opendocument.text">
+  <office:styles>
+    <style:default-style style:family="graphic">
+    </style:default-style>
+    <style:style style:name="Graphics" style:family="graphic">
+    </style:style>
+  </office:styles>
+  <office:automatic-styles>
+    <style:style style:name="fr1" style:family="graphic" style:parent-style-name="Graphics">
+      <style:graphic-properties style:run-through="foreground" style:horizontal-pos="center" style:horizontal-rel="paragraph" style:mirror="none" fo:clip="rect(0cm, 0cm, 0cm, 0cm)" draw:luminance="0%" draw:contrast="0%" draw:red="0%" draw:green="0%" draw:blue="0%" draw:gamma="100%" draw:color-inversion="false" draw:image-opacity="100%" draw:color-mode="standard"/>
+    </style:style>
+  </office:automatic-styles>
+  <office:body>
+    <office:text>
+      <text:p text:style-name="Standard"><draw:frame draw:style-name="fr1" draw:name="Image1" text:anchor-type="char" svg:width="0.041cm" svg:height="0.041cm" draw:z-index="0"><draw:image loext:mime-type="image/png"><office:binary-data>iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAAMklEQVR42mP4//8/AyWYYXAZ
+       wHSK+z8pbOoaAJIgBWM1gFh/jxqAxwCKYmHgE9KAZSYAhK3Dgc2FxfUAAAAASUVORK5CYII=
+      </office:binary-data></draw:image></draw:frame></text:p>
+    </office:text>
+  </office:body>
+</office:document>
diff --git a/vcl/qa/cppunit/pdfexport/pdfexport.cxx b/vcl/qa/cppunit/pdfexport/pdfexport.cxx
index 32288d569728..602dd6a4a0b7 100644
--- a/vcl/qa/cppunit/pdfexport/pdfexport.cxx
+++ b/vcl/qa/cppunit/pdfexport/pdfexport.cxx
@@ -149,6 +149,7 @@ public:
     //BAD CPPUNIT_TEST(testTdf106972Pdf17);
     //BAD CPPUNIT_TEST(testTdf107018);
     //BAD CPPUNIT_TEST(testTdf107089);
+    void testReduceSmallImage();
 
     CPPUNIT_TEST_SUITE(PdfExportTest);
     // CPPUNIT_TEST(testTdf106059);
@@ -186,6 +187,7 @@ public:
     CPPUNIT_TEST(testTdf115967);
     CPPUNIT_TEST(testTdf121615);
     CPPUNIT_TEST(testTocLink);
+    CPPUNIT_TEST(testReduceSmallImage);
     CPPUNIT_TEST_SUITE_END();
 };
 
@@ -1830,6 +1832,45 @@ void PdfExportTest::testTocLink()
     CPPUNIT_ASSERT(FPDFLink_Enumerate(pPdfPage.get(), &nStartPos, &pLinkAnnot));
 }
 
+void PdfExportTest::testReduceSmallImage()
+{
+    // Load the Writer document.
+    OUString aURL = m_directories.getURLFromSrc(DATA_DIRECTORY) + "reduce-small-image.fodt";
+    mxComponent = loadFromDesktop(aURL);
+
+    // Save as PDF.
+    uno::Reference<frame::XStorable> xStorable(mxComponent, uno::UNO_QUERY);
+    utl::MediaDescriptor aMediaDescriptor;
+    aMediaDescriptor["FilterName"] <<= OUString("writer_pdf_Export");
+    xStorable->storeToURL(maTempFile.GetURL(), aMediaDescriptor.getAsConstPropertyValueList());
+
+    // Parse the PDF: get the image.
+    SvFileStream aFile(maTempFile.GetURL(), StreamMode::READ);
+    maMemory.WriteStream(aFile);
+    DocumentHolder pPdfDocument(
+    FPDF_LoadMemDocument(maMemory.GetData(), maMemory.GetSize(), /*password=*/nullptr));
+    CPPUNIT_ASSERT(pPdfDocument.get());
+    CPPUNIT_ASSERT_EQUAL(1, FPDF_GetPageCount(pPdfDocument.get()));
+    PageHolder pPdfPage(FPDF_LoadPage(pPdfDocument.get(), /*page_index=*/0));
+    CPPUNIT_ASSERT(pPdfPage.get());
+    CPPUNIT_ASSERT_EQUAL(1, FPDFPage_CountObjects(pPdfPage.get()));
+    FPDF_PAGEOBJECT pPageObject = FPDFPage_GetObject(pPdfPage.get(), 0);
+    CPPUNIT_ASSERT_EQUAL(FPDF_PAGEOBJ_IMAGE, FPDFPageObj_GetType(pPageObject));
+
+    // Make sure we don't scale down a tiny bitmap.
+    FPDF_BITMAP pBitmap = FPDFImageObj_GetBitmap(pPageObject);
+    CPPUNIT_ASSERT(pBitmap);
+    int nWidth = FPDFBitmap_GetWidth(pBitmap);
+    int nHeight = FPDFBitmap_GetHeight(pBitmap);
+    FPDFBitmap_Destroy(pBitmap);
+    // Without the accompanying fix in place, this test would have failed with:
+    // - Expected: 16
+    // - Actual  : 6
+    // i.e. the image was scaled down to 300 DPI, even if it had tiny size.
+    CPPUNIT_ASSERT_EQUAL(16, nWidth);
+    CPPUNIT_ASSERT_EQUAL(16, nHeight);
+}
+
 CPPUNIT_TEST_SUITE_REGISTRATION(PdfExportTest);
 
 }
diff --git a/vcl/source/gdi/pdfwriter_impl2.cxx b/vcl/source/gdi/pdfwriter_impl2.cxx
index 5e5c0e5fbf6a..5edf11eba18d 100644
--- a/vcl/source/gdi/pdfwriter_impl2.cxx
+++ b/vcl/source/gdi/pdfwriter_impl2.cxx
@@ -110,11 +110,13 @@ void PDFWriterImpl::implWriteBitmapEx( const Point& i_rPoint, const Size& i_rSiz
         bIsPng = (eType == GfxLinkType::NativePng);
     }
 
-    if( i_rContext.m_nMaxImageResolution > 50 )
+    // Do not downsample images smaller than 50x50px.
+    const Size aBmpSize(aBitmapEx.GetSizePixel());
+    if (i_rContext.m_nMaxImageResolution > 50 && aBmpSize.getWidth() > 50
+        && aBmpSize.getHeight() > 50)
     {
         // do downsampling if necessary
         const Size      aDstSizeTwip( i_pDummyVDev->PixelToLogic(i_pDummyVDev->LogicToPixel(aSize), MapMode(MapUnit::MapTwip)) );
-        const Size      aBmpSize( aBitmapEx.GetSizePixel() );
         const double    fBmpPixelX = aBmpSize.Width();
         const double    fBmpPixelY = aBmpSize.Height();
         const double    fMaxPixelX = aDstSizeTwip.Width() * i_rContext.m_nMaxImageResolution / 1440.0;