fdo#47553: UniscribeLayout: adjust mnSubStringMin

... to actual minimum so that the fix for fdo#33090 in
UniscribeLayout::GetNextGlyphs subtracts exactly the right number.

The original value of mnSubStringMin is guessed and may be up to 8
smaller than the actual start of the first VisualItem.

For the bugdoc it happens that sometimes it's too small by 8 and then
the wrong entries in mpGlyphs2Chars are initialized and then apparently
there are single glyphs that represent multiple characters and so
GetNextGlyphs returns a -1 character which is invalid.

 ->GetNextGlyphs dir 1 36 mnSubStringMin 28
 ->GetNextGlyphs g2c #1 [8] = 36
 ->GetNextGlyphs g2c #1 [9] = 37
 ->GetNextGlyphs g2c #1 [10] = 38
 ->GetNextGlyphs g2c #1 [11] = 39
 ->GetNextGlyphs g2c #1 [12] = 40
 ->GetNextGlyphs g2c #2 [4] = 40
 ->GetNextGlyphs g2c #2 [3] = 39
 ->GetNextGlyphs g2c #2 [1] = 38
 ->GetNextGlyphs g2c #2 [1] = 37
 ->GetNextGlyphs g2c #2 [0] = 36
...
 ->GetNextGlyphs init nCharPos -1
 ->GetNextGlyphs g2c [2]  nCharPos -1
 ->GetNextGlyphs set pCharPosAry -1
layout[0]->GetNextGlyphs 768,1024 a1800 c-1 0

Change-Id: Ie33ec797a412aa898bec3f4e8f97b88dcfed4d11

1 files changed, 9 insertions, 0 deletions

diff --git a/vcl/win/source/gdi/winlayout.cxx b/vcl/win/source/gdi/winlayout.cxx
index fcc5fdcd2578..abd5144084e5 100644
--- a/vcl/win/source/gdi/winlayout.cxx
+++ b/vcl/win/source/gdi/winlayout.cxx
@@ -1331,6 +1331,12 @@ bool UniscribeLayout::LayoutText( ImplLayoutArgs& rArgs )
         {
             for( int j = rVisualItem.mnMinCharPos; j < rVisualItem.mnEndCharPos; ++j )
                 mpLogClusters[j] = sal::static_int_cast<WORD>(~0U);
+            if (rArgs.mnMinCharPos >= rVisualItem.mnEndCharPos)
+            {   // fdo#47553 adjust "guessed" min (maybe up to -8 off) to
+                // actual min so it can be used properly in GetNextGlyphs
+                assert(mnSubStringMin <= rVisualItem.mnEndCharPos);
+                mnSubStringMin = rVisualItem.mnEndCharPos;
+            }
             continue;
         }
 
@@ -1785,7 +1791,10 @@ int UniscribeLayout::GetNextGlyphs( int nLen, sal_GlyphId* pGlyphs, Point& rPos,
         int nGlyphWidth = pGlyphWidths[ nStart ];
         int nCharPos = -1;    // no need to determine charpos
         if( mpGlyphs2Chars )  // unless explicitly requested+provided
+        {
             nCharPos = mpGlyphs2Chars[ nStart ];
+            assert(-1 != nCharPos);
+        }
 
         // inject kashida glyphs if needed
         if( !mbDisableGlyphInjection