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>

1 files changed, 20 insertions, 4 deletions

diff --git a/emfio/source/reader/wmfreader.cxx b/emfio/source/reader/wmfreader.cxx
index 8a54b21f0580..33ef9dd3d0e1 100644
--- a/emfio/source/reader/wmfreader.cxx
+++ b/emfio/source/reader/wmfreader.cxx
@@ -1351,11 +1351,11 @@ 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);
@@ -1608,9 +1608,10 @@ namespace emfio
         Point aViewportOrg(0,0);
         std::optional<Size>  aViewportExt;
 
+        MappingMode eMapMode = MappingMode::MM_ANISOTROPIC;
+
         if (nEnd - nPos)
         {
-            MappingMode eMapMode = MappingMode::MM_ANISOTROPIC;
             sal_uInt16 nFunction;
             sal_uInt32 nRSize;
 
@@ -1952,6 +1953,21 @@ namespace emfio
         if (aWinExt)
         {
             rPlaceableBound = tools::Rectangle(aWinOrg, *aWinExt);
+            if (mbPlaceable && eMapMode == 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());