3 files changed, 71 insertions, 2 deletions

diff --git a/src/gui/kernel/qevent.cpp b/src/gui/kernel/qevent.cpp
index 916b13df44..139b36ef71 100644
--- a/src/gui/kernel/qevent.cpp
+++ b/src/gui/kernel/qevent.cpp
@@ -972,6 +972,7 @@ QWheelEvent::QWheelEvent(const QPointF &pos, const QPointF& globalPos,
     \li scrolling is about to begin, but the distance did not yet change (Qt::ScrollBegin),
     \li or scrolling has ended and the distance did not change anymore (Qt::ScrollEnd).
     \endlist
+    \note On X11 this value is driver specific and unreliable, use angleDelta() instead
 */
 
 /*!
diff --git a/src/gui/text/qfontdatabase.cpp b/src/gui/text/qfontdatabase.cpp
index 2cc071d67b..33dc27983a 100644
--- a/src/gui/text/qfontdatabase.cpp
+++ b/src/gui/text/qfontdatabase.cpp
@@ -2837,6 +2837,41 @@ QString QFontDatabase::resolveFontFamilyAlias(const QString &family)
     return QGuiApplicationPrivate::platformIntegration()->fontDatabase()->resolveFontFamilyAlias(family);
 }
 
+Q_GUI_EXPORT QStringList qt_sort_families_by_writing_system(QChar::Script script, const QStringList &families)
+{
+    size_t writingSystem = std::find(scriptForWritingSystem,
+                                     scriptForWritingSystem + QFontDatabase::WritingSystemsCount,
+                                     script) - scriptForWritingSystem;
+    if (writingSystem == QFontDatabase::Any
+            || writingSystem >= QFontDatabase::WritingSystemsCount) {
+        return families;
+    }
+
+    QFontDatabasePrivate *db = privateDb();
+    QMultiMap<uint, QString> supported;
+    for (int i = 0; i < families.size(); ++i) {
+        const QString &family = families.at(i);
+
+        QtFontFamily *testFamily = nullptr;
+        for (int x = 0; x < db->count; ++x) {
+            if (Q_UNLIKELY(matchFamilyName(family, db->families[x]))) {
+                testFamily = db->families[x];
+                testFamily->ensurePopulated();
+                break;
+            }
+        }
+
+        uint order = i;
+        if (testFamily == nullptr
+              || (testFamily->writingSystems[writingSystem] & QtFontFamily::Supported) == 0) {
+            order |= 1 << 31;
+        }
+
+        supported.insert(order, family);
+    }
+
+    return supported.values();
+}
 
 QT_END_NAMESPACE
 
diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index e4f9b8b9d4..33df020a6c 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2018 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtGui module of the Qt Toolkit.
@@ -1845,7 +1845,12 @@ QFontEngine *QFontEngineMulti::loadEngine(int at)
     request.styleStrategy |= QFont::NoFontMerging;
     request.family = fallbackFamilyAt(at - 1);
 
-    if (QFontEngine *engine = QFontDatabase::findFont(request, m_script)) {
+    // At this point, the main script of the text has already been considered
+    // when fetching the list of fallback families from the database, and the
+    // info about the actual script of the characters may have been discarded,
+    // so we do not check for writing system support, but instead just load
+    // the family indiscriminately.
+    if (QFontEngine *engine = QFontDatabase::findFont(request, QFontDatabase::Any)) {
         engine->fontDef.weight = request.weight;
         if (request.style > QFont::StyleNormal)
             engine->fontDef.style = request.style;
@@ -1898,8 +1903,33 @@ bool QFontEngineMulti::stringToCMap(const QChar *str, int len,
 
     int glyph_pos = 0;
     QStringIterator it(str, str + len);
+
+    int lastFallback = -1;
     while (it.hasNext()) {
         const uint ucs4 = it.peekNext();
+
+        // If we applied a fallback font to previous glyph, and the current is either
+        // ZWJ or ZWNJ, we should also try applying the same fallback font to that, in order
+        // to get the correct shaping rules applied.
+        if (lastFallback >= 0 && (ucs4 == QChar(0x200d) || ucs4 == QChar(0x200c))) {
+            QFontEngine *engine = m_engines.at(lastFallback);
+            glyph_t glyph = engine->glyphIndex(ucs4);
+            if (glyph != 0) {
+                glyphs->glyphs[glyph_pos] = glyph;
+                if (!(flags & GlyphIndicesOnly)) {
+                    QGlyphLayout g = glyphs->mid(glyph_pos, 1);
+                    engine->recalcAdvances(&g, flags);
+                }
+
+                // set the high byte to indicate which engine the glyph came from
+                glyphs->glyphs[glyph_pos] |= (lastFallback << 24);
+            } else {
+                lastFallback = -1;
+            }
+        } else {
+            lastFallback = -1;
+        }
+
         if (glyphs->glyphs[glyph_pos] == 0
                 && ucs4 != QChar::LineSeparator
                 && ucs4 != QChar::LineFeed
@@ -1928,6 +1958,9 @@ bool QFontEngineMulti::stringToCMap(const QChar *str, int len,
                         QGlyphLayout g = glyphs->mid(glyph_pos, 1);
                         engine->recalcAdvances(&g, flags);
                     }
+
+                    lastFallback = x;
+
                     // set the high byte to indicate which engine the glyph came from
                     glyphs->glyphs[glyph_pos] |= (x << 24);
                     break;