Fix harfbuzz font lifecycle in CommonSalLayout

The harfbuzz font is attached to the system font face and
therefore inherits its lifecycle. This means it can be used in
multiple CommonSalLayout objects, so the user data parameter of
hb_face_create_for_tables can't be the layout, but must be the
font.

This moves the special Qt5Font handling into it's own function,
so accessing the switching parameter mbUseQt5 is not needed.

Regression from commit b66a7cbd.

Change-Id: Ic34cc5b60e401562c73b239a58176a59fe4bf9be
Reviewed-on: https://gerrit.libreoffice.org/44398Reviewed-by: Khaled Hosny <khaledhosny@eglug.org>
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>

vcl/inc/CommonSalLayout.hxx

@@ -60,7 +60,12 @@ class VCL_DLLPUBLIC CommonSalLayout : public GenericSalLayout
 #if ENABLE_QT5
     const bool              mbUseQt5;
     Qt5Font*                mpQFont;
+
+    explicit                CommonSalLayout(const FontSelectPattern &rFSP,
+                                            FreetypeFont *pFreetypeFont,
+                                            Qt5Font *pFont, bool bUseQt5);
 #endif
+    void                    InitFromFreetypeFont();
 #endif
 
     void                    ParseFeatures(const OUString& name);
@@ -88,9 +93,6 @@ public:
     explicit                CommonSalLayout(FreetypeFont&);
     const FreetypeFont*     getFreetypeFont() const { return mpFreetypeFont; }
 #if ENABLE_QT5
-    explicit                CommonSalLayout(const FontSelectPattern &rFSP,
-                                            FreetypeFont *pFreetypeFont,
-                                            Qt5Font *pFont, bool bUseQt5);
     explicit                CommonSalLayout(Qt5Font&);
     const Qt5Font*          getQt5Font() const { return mpQFont; }
     bool                    useQt5() const { return mbUseQt5; }

vcl/source/gdi/CommonSalLayout.cxx

@@ -34,14 +34,19 @@
 #include <QtGui/QRawFont>
 #endif
 
-static hb_blob_t* getFontTable(hb_face_t* /*face*/, hb_tag_t nTableTag, void* pUserData)
+static inline void decode_hb_tag( const hb_tag_t nTableTag, char *pTagName )
 {
-    char pTagName[5];
     pTagName[0] = (char)(nTableTag >> 24);
     pTagName[1] = (char)(nTableTag >> 16);
     pTagName[2] = (char)(nTableTag >>  8);
     pTagName[3] = (char)nTableTag;
     pTagName[4] = 0;
+}
+
+static hb_blob_t* getFontTable(hb_face_t* /*face*/, hb_tag_t nTableTag, void* pUserData)
+{
+    char pTagName[5];
+    decode_hb_tag( nTableTag, pTagName );
 
     sal_uLong nLength = 0;
 #if defined(_WIN32)
@@ -67,23 +72,9 @@ static hb_blob_t* getFontTable(hb_face_t* /*face*/, hb_tag_t nTableTag, void* pU
         pFont->GetFontTable(pTagName, pBuffer);
     }
 #else
-    const char* pBuffer = nullptr;
-    CommonSalLayout *pLayout = static_cast<CommonSalLayout*>( pUserData );
-#if ENABLE_QT5
-    QByteArray aTable;
-    if ( pLayout->useQt5() )
-    {
-        QRawFont aRawFont( QRawFont::fromFont( *pLayout->getQt5Font() ) );
-        aTable = aRawFont.fontTable( pTagName );
-        pBuffer = reinterpret_cast<const char*>( aTable.data() );
-        nLength = aTable.size();
-    }
-    else
-#endif
-    {
-        pBuffer = reinterpret_cast<const char*>(
-            pLayout->getFreetypeFont()->GetTable(pTagName, &nLength) );
-    }
+    FreetypeFont* pFont = static_cast<FreetypeFont*>( pUserData );
+    const char* pBuffer = reinterpret_cast<const char*>(
+        pFont->GetTable(pTagName, &nLength) );
 #endif
 
     hb_blob_t* pBlob = nullptr;
@@ -98,6 +89,25 @@ static hb_blob_t* getFontTable(hb_face_t* /*face*/, hb_tag_t nTableTag, void* pU
     return pBlob;
 }
 
+#if ENABLE_QT5
+static hb_blob_t* getFontTable_Qt5Font(hb_face_t* /*face*/, hb_tag_t nTableTag, void* pUserData)
+{
+    char pTagName[5];
+    decode_hb_tag( nTableTag, pTagName );
+
+    Qt5Font *pFont = static_cast<Qt5Font*>( pUserData );
+    QRawFont aRawFont( QRawFont::fromFont( *pFont ) );
+    QByteArray aTable = aRawFont.fontTable( pTagName );
+    const sal_uLong nLength = aTable.size();
+
+    hb_blob_t* pBlob = nullptr;
+    if (nLength > 0)
+        pBlob = hb_blob_create(reinterpret_cast<const char*>( aTable.data() ),
+                               nLength, HB_MEMORY_MODE_READONLY, nullptr, nullptr);
+    return pBlob;
+}
+#endif
+
 static hb_font_t* createHbFont(hb_face_t* pHbFace)
 {
     hb_font_t* pHbFont = hb_font_create(pHbFace);
@@ -254,6 +264,17 @@ CommonSalLayout::CommonSalLayout(const CoreTextStyle& rCoreTextStyle)
 
 #else
 
+void CommonSalLayout::InitFromFreetypeFont()
+{
+    mpHbFont = mpFreetypeFont->GetHbFont();
+    if (!mpHbFont)
+    {
+        hb_face_t* pHbFace = hb_face_create_for_tables(getFontTable, mpFreetypeFont, nullptr);
+        mpHbFont = createHbFont(pHbFace);
+        mpFreetypeFont->SetHbFont(mpHbFont);
+    }
+}
+
 #if ENABLE_QT5
 CommonSalLayout::CommonSalLayout(const FontSelectPattern &rFSP,
                                  FreetypeFont *pFreetypeFont,
@@ -265,18 +286,21 @@ CommonSalLayout::CommonSalLayout(const FontSelectPattern &rFSP,
     , mpVertGlyphs(nullptr)
 {
     if (mbUseQt5)
+    {
+        assert( pQt5Font && !pFreetypeFont );
         mpHbFont = mpQFont->GetHbFont();
+        if (!mpHbFont)
+        {
+            hb_face_t* pHbFace = hb_face_create_for_tables(
+                getFontTable_Qt5Font, pQt5Font, nullptr);
+            mpHbFont = createHbFont(pHbFace);
+            mpQFont->SetHbFont(mpHbFont);
+        }
+    }
     else
-        mpHbFont = mpFreetypeFont->GetHbFont();
-    if (!mpHbFont)
     {
-        hb_face_t* pHbFace = hb_face_create_for_tables(getFontTable, this, nullptr);
-
-        mpHbFont = createHbFont(pHbFace);
-        if (mbUseQt5)
-            mpQFont->SetHbFont(mpHbFont);
-        else
-            mpFreetypeFont->SetHbFont(mpHbFont);
+        assert( !pQt5Font && pFreetypeFont );
+        InitFromFreetypeFont();
     }
 }
 
@@ -299,13 +323,7 @@ CommonSalLayout::CommonSalLayout(FreetypeFont& rFreetypeFont)
     , mpFreetypeFont(&rFreetypeFont)
     , mpVertGlyphs(nullptr)
 {
-    mpHbFont = mpFreetypeFont->GetHbFont();
-    if (!mpHbFont)
-    {
-        hb_face_t* pHbFace = hb_face_create_for_tables(getFontTable, this, nullptr);
-        mpHbFont = createHbFont(pHbFace);
-        mpFreetypeFont->SetHbFont(mpHbFont);
-    }
+    InitFromFreetypeFont();
 }
 
 #endif