tdf#150888 Scale down PPI if it would result in a tiny image

The reason for the blurry document in tdf#150888 is that the image is
tiny. PPI is 2540 in that image but when using the window bounding box
(96, 81) this results in a very small image that the .odt then scales up
which makes it blurry.

Apart from that, when opening the extracted .wmf in Draw it's also very
small, around 0.04" squared.

Because MM_ANISOTROPICs definition allows for arbritrary scaling, when
an image would be smaller than an inch squared the PPI is scaled down to
either the images width or height. This makes the extracted WMF match
the size of competitor office suites and fix the blur bug without
breaking past tests.

Change-Id: I11eab879848d9308f818708a91fd9eb91fc65200
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/141533
Tested-by: Jenkins
Tested-by: Tomaž Vajngerl <quikee@gmail.com>
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
(cherry picked from commit a03a47bb0791d88fedb2650bca412c28469b0b27)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/141775
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>

4 files changed, 45 insertions, 4 deletions

diff --git a/emfio/inc/wmfreader.hxx b/emfio/inc/wmfreader.hxx
index f7788d53651c..5c6979550ef4 100644
--- a/emfio/inc/wmfreader.hxx
+++ b/emfio/inc/wmfreader.hxx
@@ -33,6 +33,7 @@ namespace emfio
     private:
         sal_uInt16      mnUnitsPerInch;
         sal_uInt32      mnRecSize;
+        bool            mbPlaceable;
 
         // embedded EMF data
         std::optional<std::vector<sal_uInt8>> mpEMFStream;
diff --git a/emfio/qa/cppunit/wmf/data/TestBigPPI.wmf b/emfio/qa/cppunit/wmf/data/TestBigPPI.wmf
new file mode 100644
index 000000000000..e120af2790db
--- /dev/null
+++ b/emfio/qa/cppunit/wmf/data/TestBigPPI.wmf
diff --git a/emfio/qa/cppunit/wmf/wmfimporttest.cxx b/emfio/qa/cppunit/wmf/wmfimporttest.cxx
index d6533d8ba07c..33cf3f546c92 100644
--- a/emfio/qa/cppunit/wmf/wmfimporttest.cxx
+++ b/emfio/qa/cppunit/wmf/wmfimporttest.cxx
@@ -52,6 +52,7 @@ public:
     void testEmfProblem();
     void testEmfLineStyles();
     void testWorldTransformFontSize();
+    void testBigPPI();
     void testTdf93750();
     void testTdf99402();
     void testTdf39894();
@@ -65,6 +66,7 @@ public:
     CPPUNIT_TEST(testEmfProblem);
     CPPUNIT_TEST(testEmfLineStyles);
     CPPUNIT_TEST(testWorldTransformFontSize);
+    CPPUNIT_TEST(testBigPPI);
     CPPUNIT_TEST(testTdf93750);
     CPPUNIT_TEST(testTdf99402);
     CPPUNIT_TEST(testTdf39894);
@@ -308,6 +310,27 @@ void WmfTest::testWorldTransformFontSize()
     assertXPath(pDoc, "/metafile/font[4]", "weight", "normal");
 }
 
+void WmfTest::testBigPPI()
+{
+    // Test that PPI is reduced from 2540 to 96 (width from META_SETWINDOWEXT) to make the graphic
+    // bigger
+    SvFileStream aFileStream(getFullUrl(u"TestBigPPI.wmf"), StreamMode::READ);
+    GDIMetaFile aGDIMetaFile;
+    ReadWindowMetafile(aFileStream, aGDIMetaFile);
+
+    MetafileXmlDump dumper;
+    dumper.filterAllActionTypes();
+    dumper.filterActionType(MetaActionType::FONT, false);
+    xmlDocUniquePtr pDoc = dumpAndParse(dumper, aGDIMetaFile);
+
+    CPPUNIT_ASSERT(pDoc);
+
+    // If the PPI was not reduced the width and height would be <100 which is too small
+    // Related: tdf#150888
+    assertXPath(pDoc, "/metafile", "width", "2540");
+    assertXPath(pDoc, "/metafile", "height", "2143");
+}
+
 void WmfTest::testTdf93750()
 {
     SvFileStream aFileStream(getFullUrl(u"tdf93750.emf"), StreamMode::READ);
diff --git a/emfio/source/reader/wmfreader.cxx b/emfio/source/reader/wmfreader.cxx
index c4d21b3231b1..f17654097ba0 100644
--- a/emfio/source/reader/wmfreader.cxx
+++ b/emfio/source/reader/wmfreader.cxx
@@ -1412,11 +1412,11 @@ namespace emfio
 
         tools::Rectangle aPlaceableBound;
 
-        bool bPlaceable = nPlaceableMetaKey == 0x9ac6cdd7L;
+        mbPlaceable = nPlaceableMetaKey == 0x9ac6cdd7L;
 
-        SAL_INFO("emfio", "Placeable: \"" << (bPlaceable ? "yes" : "no") << "\"");
+        SAL_INFO("emfio", "Placeable: \"" << (mbPlaceable ? "yes" : "no") << "\"");
 
-        if (bPlaceable)
+        if (mbPlaceable)
         {
             //TODO do some real error handling here
             sal_Int16 nVal(0);
@@ -1669,9 +1669,10 @@ namespace emfio
         Point aViewportOrg(0,0);
         std::optional<Size>  aViewportExt;
 
+        sal_Int16 nMapMode = MM_ANISOTROPIC;
+
         if (nEnd - nPos)
         {
-            sal_Int16 nMapMode = MM_ANISOTROPIC;
             sal_uInt16 nFunction;
             sal_uInt32 nRSize;
 
@@ -2001,6 +2002,21 @@ namespace emfio
         if (aWinExt)
         {
             rPlaceableBound = tools::Rectangle(aWinOrg, *aWinExt);
+            if (mbPlaceable && nMapMode == MM_ANISOTROPIC)
+            {
+                // It seems that (in MM_ANISOTROPIC WMFs) the "inch" field (PPI) in META_PLACEABLE is
+                // ignored and instead competitor office suites decide what it should be arbitrarily
+                // Could have to do with MM_ANISOTROPICs definition:
+                // Logical units are mapped to arbitrary units with arbitrarily scaled axes.
+                // The issue is that when PPI is bigger than the window size, the image appears
+                // tiny (smaller than an inch squared).
+                // A solution is to scale PPI down in such images to an arbitrary amount that makes
+                // the image visible:
+                auto nWidth = rPlaceableBound.GetWidth();
+                auto nHeight = rPlaceableBound.GetHeight();
+                if (mnUnitsPerInch > nWidth && mnUnitsPerInch > nHeight)
+                    mnUnitsPerInch = std::max(nWidth, nHeight);
+            }
             SAL_INFO("emfio", "Window dimension "
                        " left: " << rPlaceableBound.Left()  << " top: " << rPlaceableBound.Top()
                     << " right: " << rPlaceableBound.Right() << " bottom: " << rPlaceableBound.Bottom());
@@ -2035,6 +2051,7 @@ namespace emfio
         : MtfTools(rGDIMetaFile, rStreamWMF)
         , mnUnitsPerInch(96)
         , mnRecSize(0)
+        , mbPlaceable(false)
         , mnEMFRecCount(0)
         , mnEMFRec(0)
         , mnEMFSize(0)