Fix several regressions in font selection

In Qt 5.3.0 a change was added which automatically adapts Common
script to surrounding scripts in accordance with the Unicode tr#24.

This broke *a lot* of cases of font selection because the font
selection algorithm is not prepared for handling characters with
adapted scripts. We need to disable this change for now and redo it
later with patches to font selection to avoid the regressions.

[ChangeLog][Text] Fixed several regressions in font selection when
combining different writing systems in the same text.

Task-number: QTBUG-39930
Task-number: QTBUG-39860
Change-Id: Id02b5ae2403c06542ed5d81e7c4deb2e0c7d816e
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>

5 files changed, 41 insertions, 9 deletions

diff --git a/src/corelib/tools/qunicodetools.cpp b/src/corelib/tools/qunicodetools.cpp
index fc36d07a4a..bb2c032e57 100644
--- a/src/corelib/tools/qunicodetools.cpp
+++ b/src/corelib/tools/qunicodetools.cpp
@@ -710,6 +710,7 @@ Q_CORE_EXPORT void initScripts(const ushort *string, int length, uchar *scripts)
             script = QChar::Script(prop->script);
         }
 
+#if 0 // ### Disabled due to regressions. The font selection algorithm is not prepared for this change.
         if (Q_LIKELY(script != QChar::Script_Common)) {
             // override preceding Common-s
             while (sor > 0 && scripts[sor - 1] == QChar::Script_Common)
@@ -719,6 +720,7 @@ Q_CORE_EXPORT void initScripts(const ushort *string, int length, uchar *scripts)
             if (sor > 0)
                 script = scripts[sor - 1];
         }
+#endif
 
         while (sor < eor)
             scripts[sor++] = script;
@@ -726,6 +728,8 @@ Q_CORE_EXPORT void initScripts(const ushort *string, int length, uchar *scripts)
         script = prop->script;
     }
     eor = length;
+
+#if 0 // ### Disabled due to regressions. The font selection algorithm is not prepared for this change.
     if (Q_LIKELY(script != QChar::Script_Common)) {
         // override preceding Common-s
         while (sor > 0 && scripts[sor - 1] == QChar::Script_Common)
@@ -735,6 +739,8 @@ Q_CORE_EXPORT void initScripts(const ushort *string, int length, uchar *scripts)
         if (sor > 0)
             script = scripts[sor - 1];
     }
+#endif
+
     while (sor < eor)
         scripts[sor++] = script;
 }
diff --git a/src/gui/text/qtextengine.cpp b/src/gui/text/qtextengine.cpp
index a3059008be..fcf1a1468c 100644
--- a/src/gui/text/qtextengine.cpp
+++ b/src/gui/text/qtextengine.cpp
@@ -124,7 +124,7 @@ private:
         for (int i = start + 1; i < end; ++i) {
             if (m_analysis[i].bidiLevel == m_analysis[start].bidiLevel
                 && m_analysis[i].flags == m_analysis[start].flags
-                && m_analysis[i].script == m_analysis[start].script
+                && (m_analysis[i].script == m_analysis[start].script || m_string[i] == QLatin1Char('.'))
                 && m_analysis[i].flags < QScriptAnalysis::SpaceTabOrObject
                 && i - start < MaxItemLength)
                 continue;
diff --git a/tests/auto/gui/text/qglyphrun/test.ttf b/tests/auto/gui/text/qglyphrun/test.ttf
index 9043a576ef..382b2547b0 100644
--- a/tests/auto/gui/text/qglyphrun/test.ttf
+++ b/tests/auto/gui/text/qglyphrun/test.ttf
diff --git a/tests/auto/gui/text/qglyphrun/tst_qglyphrun.cpp b/tests/auto/gui/text/qglyphrun/tst_qglyphrun.cpp
index f576627745..8d1ec51c26 100644
--- a/tests/auto/gui/text/qglyphrun/tst_qglyphrun.cpp
+++ b/tests/auto/gui/text/qglyphrun/tst_qglyphrun.cpp
@@ -77,6 +77,7 @@ private slots:
     void setRawData();
     void setRawDataAndGetAsVector();
     void boundingRect();
+    void mixedScripts();
 
 private:
     int m_testFontId;
@@ -399,7 +400,7 @@ void tst_QGlyphRun::setRawDataAndGetAsVector()
 void tst_QGlyphRun::drawNonExistentGlyphs()
 {
     QVector<quint32> glyphIndexes;
-    glyphIndexes.append(3);
+    glyphIndexes.append(4);
 
     QVector<QPointF> glyphPositions;
     glyphPositions.append(QPointF(0, 0));
@@ -725,6 +726,23 @@ void tst_QGlyphRun::boundingRect()
     QCOMPARE(glyphs.boundingRect(), boundingRect);
 }
 
+void tst_QGlyphRun::mixedScripts()
+{
+    QString s;
+    s += QChar(0x31); // The character '1'
+    s += QChar(0xbc14); // Hangul character
+
+    QTextLayout layout;
+    layout.setFont(m_testFont);
+    layout.setText(s);
+    layout.beginLayout();
+    layout.createLine();
+    layout.endLayout();
+
+    QList<QGlyphRun> glyphRuns = layout.glyphRuns();
+    QCOMPARE(glyphRuns.size(), 2);
+}
+
 #endif // QT_NO_RAWFONT
 
 QTEST_MAIN(tst_QGlyphRun)
diff --git a/tests/auto/gui/text/qtextscriptengine/tst_qtextscriptengine.cpp b/tests/auto/gui/text/qtextscriptengine/tst_qtextscriptengine.cpp
index 74eb58670b..5dfb025510 100644
--- a/tests/auto/gui/text/qtextscriptengine/tst_qtextscriptengine.cpp
+++ b/tests/auto/gui/text/qtextscriptengine/tst_qtextscriptengine.cpp
@@ -1258,21 +1258,29 @@ void tst_QTextScriptEngine::thaiWithZWJ()
     QTextLayout layout(s, font);
     QTextEngine *e = layout.engine();
     e->itemize();
-    QCOMPARE(e->layoutData->items.size(), 3);
+    QCOMPARE(e->layoutData->items.size(), 11);
 
     for (int item = 0; item < e->layoutData->items.size(); ++item)
         e->shape(item);
 
-    QCOMPARE(e->layoutData->items[0].num_glyphs, ushort(15)); // Thai: The ZWJ and ZWNJ characters are inherited, so should be part of the thai script
-    QCOMPARE(e->layoutData->items[1].num_glyphs, ushort(1));  // Han: Kanji for tree
-    QCOMPARE(e->layoutData->items[2].num_glyphs, ushort(2));  // Thai: Thai character followed by superscript "a" which is of inherited type
+    QCOMPARE(e->layoutData->items[0].num_glyphs, ushort(7));  // Thai: The ZWJ and ZWNJ characters are inherited, so should be part of the thai script
+    QCOMPARE(e->layoutData->items[1].num_glyphs, ushort(1));  // Common: The smart quotes cannot be handled by thai, so should be a separate item
+    QCOMPARE(e->layoutData->items[2].num_glyphs, ushort(1));  // Thai: Thai character
+    QCOMPARE(e->layoutData->items[3].num_glyphs, ushort(1));  // Common: Ellipsis
+    QCOMPARE(e->layoutData->items[4].num_glyphs, ushort(1));  // Thai: Thai character
+    QCOMPARE(e->layoutData->items[5].num_glyphs, ushort(1));  // Common: Smart quote
+    QCOMPARE(e->layoutData->items[6].num_glyphs, ushort(1));  // Thai: Thai character
+    QCOMPARE(e->layoutData->items[7].num_glyphs, ushort(1));  // Common: \xA0 = non-breaking space. Could be useful to have in thai, but not currently implemented
+    QCOMPARE(e->layoutData->items[8].num_glyphs, ushort(1));  // Thai: Thai character
+    QCOMPARE(e->layoutData->items[9].num_glyphs, ushort(1));  // Japanese: Kanji for tree
+    QCOMPARE(e->layoutData->items[10].num_glyphs, ushort(2)); // Thai: Thai character followed by superscript "a" which is of inherited type
 
     //A quick sanity check - check all the characters are individual clusters
     unsigned short *logClusters = e->layoutData->logClustersPtr;
-    for (int i = 0; i <= 14; i++)
+    for (int i = 0; i < 7; i++)
         QCOMPARE(logClusters[i], ushort(i));
-    QCOMPARE(logClusters[15], ushort(0));
-    QCOMPARE(logClusters[16], ushort(0));
+    for (int i = 0; i < 10; i++)
+        QCOMPARE(logClusters[i+7], ushort(0));
 #ifndef Q_OS_MAC
     // ### Result differs for HarfBuzz-NG
     QCOMPARE(logClusters[17], ushort(1));