Use new line heights only if SAL_USE_NEW_LINEHEIGHT=1

Commit 3364fefe introduced a new (and
font technically correct) handling of interline spacing that affects
line heights in all applications. Activate that only if
SAL_USE_NEW_LINEHEIGHT=1 is set in the environment, else use the old
handling until all quirks are sorted out.

vcl/unx/generic/glyphs/gcach_ftyp.cxx

@@ -951,6 +951,18 @@ int ServerFont::GetEmUnits() const
 
 void ServerFont::FetchFontMetric( ImplFontMetricData& rTo, long& rFactor ) const
 {
+    const int UNDETERMINED = 0xFEED;
+    static int nUseNewLineHeight = UNDETERMINED;
+    if (nUseNewLineHeight == UNDETERMINED)
+    {
+        osl::MutexGuard aGuard( osl::Mutex::getGlobalMutex());
+        if (nUseNewLineHeight == UNDETERMINED)
+        {
+            const char* pEnv = getenv( "SAL_USE_NEW_LINEHEIGHT");
+            nUseNewLineHeight = (pEnv ? atoi(pEnv) : 0);
+        }
+    }
+
     static_cast<ImplFontAttributes&>(rTo) = mpFontInfo->GetFontAttributes();
 
     rTo.mbScalableFont  = true;
@@ -977,8 +989,15 @@ void ServerFont::FetchFontMetric( ImplFontMetricData& rTo, long& rFactor ) const
     const FT_Size_Metrics& rMetrics = maFaceFT->size->metrics;
     rTo.mnAscent            = (+rMetrics.ascender + 32) >> 6;
     rTo.mnDescent           = (-rMetrics.descender + 32) >> 6;
-    rTo.mnExtLeading        = ((rMetrics.height + 32) >> 6) - (rTo.mnAscent + rTo.mnDescent);
-    rTo.mnIntLeading        = (rTo.mnAscent + rTo.mnDescent) - ((maFaceFT->units_per_EM + 32) >> 6);
+    if (nUseNewLineHeight)
+    {
+        rTo.mnExtLeading    = ((rMetrics.height + 32) >> 6) - (rTo.mnAscent + rTo.mnDescent);
+        rTo.mnIntLeading    = (rTo.mnAscent + rTo.mnDescent) - ((maFaceFT->units_per_EM + 32) >> 6);
+    }
+    else
+    {
+        rTo.mnIntLeading    = ((rMetrics.height + 32) >> 6) - (rTo.mnAscent + rTo.mnDescent);
+    }
     rTo.mnSlant             = 0;
 
     const TT_OS2* pOS2 = (const TT_OS2*)FT_Get_Sfnt_Table( maFaceFT, ft_sfnt_os2 );
@@ -1014,12 +1033,67 @@ void ServerFont::FetchFontMetric( ImplFontMetricData& rTo, long& rFactor ) const
         }
 
         const double fScale = (double)GetFontSelData().mnHeight / maFaceFT->units_per_EM;
-        if( pOS2->sTypoAscender || pOS2->sTypoDescender )
+        if (nUseNewLineHeight)
+        {
+            if( pOS2->sTypoAscender || pOS2->sTypoDescender )
+            {
+                rTo.mnAscent     = (long)(  pOS2->sTypoAscender  * fScale + 0.5 );
+                rTo.mnDescent    = (long)( -pOS2->sTypoDescender * fScale + 0.5 );
+                rTo.mnExtLeading = (long)(  pOS2->sTypoLineGap   * fScale + 0.5 );
+                rTo.mnIntLeading = (long)( (pOS2->sTypoAscender - pOS2->sTypoDescender - maFaceFT->units_per_EM) * fScale + 0.5 );
+            }
+        }
+        else
         {
-            rTo.mnAscent     = (long)(  pOS2->sTypoAscender  * fScale + 0.5 );
-            rTo.mnDescent    = (long)( -pOS2->sTypoDescender * fScale + 0.5 );
-            rTo.mnExtLeading = (long)(  pOS2->sTypoLineGap   * fScale + 0.5 );
-            rTo.mnIntLeading = (long)( (pOS2->sTypoAscender - pOS2->sTypoDescender - maFaceFT->units_per_EM) * fScale + 0.5 );
+            // #108862# sanity check, some fonts treat descent as signed !!!
+            int nDescent = pOS2->usWinDescent;
+            if( nDescent > 5*maFaceFT->units_per_EM )
+                nDescent = (short)pOS2->usWinDescent; // interpret it as signed!
+
+            if( pOS2->usWinAscent || pOS2->usWinDescent ) // #i30551#
+            {
+                rTo.mnAscent     = (long)( +pOS2->usWinAscent * fScale + 0.5 );
+                rTo.mnDescent    = (long)( +nDescent * fScale + 0.5 );
+                rTo.mnIntLeading = (long)( (+pOS2->usWinAscent + pOS2->usWinDescent - maFaceFT->units_per_EM) * fScale + 0.5 );
+            }
+            rTo.mnExtLeading = 0;
+            const TT_HoriHeader* pHHEA = (const TT_HoriHeader*)FT_Get_Sfnt_Table( maFaceFT, ft_sfnt_hhea );
+            if( (pHHEA != NULL) && (pOS2->usWinAscent || pOS2->usWinDescent) )
+            {
+                int nExtLeading = pHHEA->Line_Gap;
+                nExtLeading -= (pOS2->usWinAscent + pOS2->usWinDescent);
+                nExtLeading += (pHHEA->Ascender - pHHEA->Descender);
+                if( nExtLeading > 0 )
+                    rTo.mnExtLeading = (long)(nExtLeading * fScale + 0.5);
+            }
+
+            // Check for CJK capabilities of the current font
+            // #107888# workaround for Asian...
+            // TODO: remove when ExtLeading fully implemented
+            sal_Bool bCJKCapable = ((pOS2->ulUnicodeRange2 & 0x2DF00000) != 0);
+
+            if ( bCJKCapable && (pOS2->usWinAscent || pOS2->usWinDescent) )
+            {
+                rTo.mnIntLeading += rTo.mnExtLeading;
+
+                // #109280# The line height for Asian fonts is too small.
+                // Therefore we add half of the external leading to the
+                // ascent, the other half is added to the descent.
+                const long nHalfTmpExtLeading = rTo.mnExtLeading / 2;
+                const long nOtherHalfTmpExtLeading = rTo.mnExtLeading - nHalfTmpExtLeading;
+
+                // #110641# external leading for Asian fonts.
+                // The factor 0.3 has been verified during experiments.
+                const long nCJKExtLeading = (long)(0.30 * (rTo.mnAscent + rTo.mnDescent));
+
+                if ( nCJKExtLeading > rTo.mnExtLeading )
+                    rTo.mnExtLeading = nCJKExtLeading - rTo.mnExtLeading;
+                else
+                    rTo.mnExtLeading = 0;
+
+                rTo.mnAscent += nHalfTmpExtLeading;
+                rTo.mnDescent += nOtherHalfTmpExtLeading;
+            }
         }
     }