tdf#87373: Bad text spacing on OS X

Adjustments to character positions less than one pixel are ignored.
These adjustments are probably introduced by lossy conversions between
integer based and float based coordinates.

DXArray elements are adjusted to integers avoiding cummulated rounding
differences.

Change-Id: I65d476301247251a7d329b14adb70be367538c97
Reviewed-on: https://gerrit.libreoffice.org/15633
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Khaled Hosny <khaledhosny@eglug.org>

1 files changed, 42 insertions, 18 deletions

diff --git a/vcl/quartz/ctlayout.cxx b/vcl/quartz/ctlayout.cxx
index 67733de9c32e..82d9c64fdafa 100644
--- a/vcl/quartz/ctlayout.cxx
+++ b/vcl/quartz/ctlayout.cxx
@@ -215,13 +215,17 @@ void CTLayout::AdjustLayout( ImplLayoutArgs& rArgs )
         return;
     }
 
-    DeviceCoordinate nPixelWidth = 0;
-
     if(rArgs.mpDXArray && !(rArgs.mnFlags & SalLayoutFlags::BiDiRtl) )
     {
-        nPixelWidth = rArgs.mpDXArray[ mnCharCount - 1 ];
-        if( nPixelWidth <= 0)
+        DeviceCoordinate nPixelWidth = rArgs.mpDXArray[ mnCharCount - 1 ];
+
+        // justification requests which change the width by just one pixel are probably
+        // introduced by lossy conversions between integer based coordinate system
+        DeviceCoordinate nOrigWidth = lrint( GetTextWidth() );
+        if( (nPixelWidth <= 0) || ((nOrigWidth >= rint( nPixelWidth - 1 )) && (nOrigWidth <= rint( nPixelWidth + 1 ))) )
+        {
             return;
+        }
         ApplyDXArray( rArgs );
         if( mnTrailingSpaceCount )
         {
@@ -230,13 +234,15 @@ void CTLayout::AdjustLayout( ImplLayoutArgs& rArgs )
                 rArgs.mpDXArray[ mnCharCount - mnTrailingSpaceCount - 1];
             mfTrailingSpaceWidth = nFullPixelWidth - nPixelWidth;
             if( nPixelWidth <= 0)
+            {
                 return;
+            }
         }
         mfCachedWidth = nPixelWidth;
     }
     else
     {
-        nPixelWidth = rArgs.mnLayoutWidth;
+        DeviceCoordinate nPixelWidth = rArgs.mnLayoutWidth;
 
         if( nPixelWidth <= 0 && rArgs.mnFlags & SalLayoutFlags::BiDiRtl)
         {
@@ -244,7 +250,9 @@ void CTLayout::AdjustLayout( ImplLayoutArgs& rArgs )
         }
 
         if( nPixelWidth <= 0)
+        {
             return;
+        }
 
         // if the text to be justified has whitespace in it then
         // - Writer goes crazy with its HalfSpace magic
@@ -721,21 +729,27 @@ DeviceCoordinate CTLayout::GetTextWidth() const
 
 DeviceCoordinate CTLayout::FillDXArray( DeviceCoordinate* pDXArray ) const
 {
-    DeviceCoordinate nPixWidth = GetTextWidth();
+    DeviceCoordinate nPixelWidth = GetTextWidth();
+
     // short circuit requests which don't need full details
     if( !pDXArray )
-        return nPixWidth;
+    {
+        return nPixelWidth;
+    }
 
     for(int i = 0; i < mnCharCount; i++)
     {
         pDXArray[i] = 0.0;
     }
+
+    // prepare the sub-pixel accurate logical-width array
+    ::std::vector<float> aWidthVector( mnCharCount );
     if( mnTrailingSpaceCount && (mfTrailingSpaceWidth > 0.0) )
     {
         const double fOneWidth = mfTrailingSpaceWidth / mnTrailingSpaceCount;
         for(int i = mnCharCount - mnTrailingSpaceCount; i < mnCharCount; i++)
         {
-            pDXArray[i] = fOneWidth;
+            aWidthVector[i] = fOneWidth;
         }
     }
 
@@ -743,9 +757,9 @@ DeviceCoordinate CTLayout::FillDXArray( DeviceCoordinate* pDXArray ) const
     CFArrayRef aGlyphRuns = CTLineGetGlyphRuns( mpCTLine );
     const int nRunCount = CFArrayGetCount( aGlyphRuns );
     typedef std::vector<CGSize> CGSizeVector;
-    CGSizeVector aSizeVec;
+    CGSizeVector aSizeVector;
     typedef std::vector<CFIndex> CFIndexVector;
-    CFIndexVector aIndexVec;
+    CFIndexVector aIndexVector;
 
     for( int nRunIndex = 0; nRunIndex < nRunCount; ++nRunIndex )
     {
@@ -753,19 +767,29 @@ DeviceCoordinate CTLayout::FillDXArray( DeviceCoordinate* pDXArray ) const
         const CFIndex nGlyphCount = CTRunGetGlyphCount( pGlyphRun );
         const CFRange aFullRange = CFRangeMake( 0, nGlyphCount );
 
-        aSizeVec.resize( nGlyphCount );
-        aIndexVec.resize( nGlyphCount );
-        CTRunGetAdvances( pGlyphRun, aFullRange, &aSizeVec[0] );
-        CTRunGetStringIndices( pGlyphRun, aFullRange, &aIndexVec[0] );
+        aSizeVector.resize( nGlyphCount );
+        aIndexVector.resize( nGlyphCount );
+        CTRunGetAdvances( pGlyphRun, aFullRange, &aSizeVector[0] );
+        CTRunGetStringIndices( pGlyphRun, aFullRange, &aIndexVector[0] );
 
         for( int i = 0; i != nGlyphCount; ++i )
         {
-            const int nRelIdx = aIndexVec[i];
-            SAL_INFO( "vcl.ct", "pDXArray[ g:" << i << "-> c:" << nRelIdx << " ] = " << pDXArray[nRelIdx] << " + " << aSizeVec[i].width << " = " << pDXArray[nRelIdx] + aSizeVec[i].width);
-            pDXArray[nRelIdx] += aSizeVec[i].width;
+            const int nRelIndex = aIndexVector[i];
+            SAL_INFO( "vcl.ct", "aWidthVector[ g:" << i << "-> c:" << nRelIndex << " ] = " << aWidthVector[nRelIndex] << " + " << aSizeVector[i].width << " = " << aWidthVector[nRelIndex] + aSizeVector[i].width);
+            aWidthVector[nRelIndex] += aSizeVector[i].width;
         }
     }
-    return nPixWidth;
+
+    // convert the sub-pixel accurate array into classic pDXArray integers
+    float fWidthSum = 0.0;
+    sal_Int32 nOldDX = 0;
+    for( int i = 0; i < mnCharCount; ++i)
+    {
+        const sal_Int32 nNewDX = rint( fWidthSum += aWidthVector[i]);
+        pDXArray[i] = nNewDX - nOldDX;
+        nOldDX = nNewDX;
+    }
+    return nPixelWidth;
 }
 
 sal_Int32 CTLayout::GetTextBreak( DeviceCoordinate nMaxWidth, DeviceCoordinate nCharExtra, int nFactor ) const