Fix clipped text when combining multiple writing systems

When a QTextLine consists of multiple different scripts and the
fonts had negative bearing, the background for a script item could
overdraw the previous item's text, causing it to look clipped.

This was because the background and text was drawn in a single pass,
and moving the background drawing into its own pre-pass fixes the
issue.

[ChangeLog][QtGui] Fixed an issue where drawing text from different
writing systems in the same line and including a background could
cause parts of the text to be clipped.

Pick-to: 6.6 6.5
Fixes: QTBUG-121040
Change-Id: I3f79e6d33c09a2a92853bc8752dbe11a0bea2dd0
Reviewed-by: Lars Knoll <lars@knoll.priv.no>
(cherry picked from commit 8be3c9f4867ce7982387b075739b8f55c5c45753)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/text/qtextlayout.cpp

@@ -2228,20 +2228,20 @@ int QTextLine::textLength() const
     return eng->lines.at(index).length + eng->lines.at(index).trailingSpaces;
 }
 
-static void setPenAndDrawBackground(QPainter *p, const QPen &defaultPen, const QTextCharFormat &chf, const QRectF &r)
+static void drawBackground(QPainter *p, const QTextCharFormat &chf, const QRectF &r)
 {
-    QBrush c = chf.foreground();
-    if (c.style() == Qt::NoBrush) {
-        p->setPen(defaultPen);
-    }
-
     QBrush bg = chf.background();
     if (bg.style() != Qt::NoBrush && !chf.property(SuppressBackground).toBool())
         p->fillRect(r.toAlignedRect(), bg);
-    if (c.style() != Qt::NoBrush) {
-        p->setPen(QPen(c, 0));
 }
 
+static void setPen(QPainter *p, const QPen &defaultPen, const QTextCharFormat &chf)
+{
+    QBrush c = chf.foreground();
+    if (c.style() == Qt::NoBrush)
+        p->setPen(defaultPen);
+    else
+        p->setPen(QPen(c, 0));
 }
 
 #if !defined(QT_NO_RAWFONT)
@@ -2636,7 +2636,6 @@ void QTextLine::draw_internal(QPainter *p, const QPointF &origPos,
     Q_ASSERT(!eng->useRawFont);
 #endif
     const QScriptLine &line = eng->lines[index];
-    QPen pen = p->pen();
 
     bool noText = (selection && selection->format.property(SuppressText).toBool());
 
@@ -2648,8 +2647,7 @@ void QTextLine::draw_internal(QPainter *p, const QPointF &origPos,
             const qreal lineHeight = line.height().toReal();
             QRectF r(origPos.x() + line.x.toReal(), origPos.y() + line.y.toReal(),
                      lineHeight / 2, QFontMetrics(eng->font()).horizontalAdvance(u' '));
-            setPenAndDrawBackground(p, QPen(), selection->format, r);
+            drawBackground(p, selection->format, r);
-            p->setPen(pen);
         }
         return;
     }
@@ -2662,7 +2660,7 @@ void QTextLine::draw_internal(QPainter *p, const QPointF &origPos,
     else
         p->translate(origPos);
 
-    QTextLineItemIterator iterator(eng, index, pos, selection);
+
     QFixed lineBase = line.base();
     eng->clearDecorations();
     eng->enableDelayDecorations();
@@ -2672,6 +2670,39 @@ void QTextLine::draw_internal(QPainter *p, const QPointF &origPos,
     const QTextFormatCollection *formatCollection = eng->formatCollection();
 
     bool suppressColors = (eng->option.flags() & QTextOption::SuppressColors);
+
+    auto prepareFormat = [suppressColors, selection, this](QTextCharFormat &format,
+                                                           QScriptItem *si) {
+        format.merge(eng->format(si));
+
+        if (suppressColors) {
+            format.clearForeground();
+            format.clearBackground();
+            format.clearProperty(QTextFormat::TextUnderlineColor);
+        }
+        if (selection)
+            format.merge(selection->format);
+    };
+
+    {
+        QTextLineItemIterator iterator(eng, index, pos, selection);
+        while (!iterator.atEnd()) {
+            QScriptItem &si = iterator.next();
+
+            if (eng->hasFormats() || selection || formatCollection) {
+                QTextCharFormat format;
+                if (formatCollection != nullptr)
+                    format = formatCollection->defaultTextFormat();
+                prepareFormat(format, &si);
+                drawBackground(p, format, QRectF(iterator.x.toReal(), (y - lineBase).toReal(),
+                                                 iterator.itemWidth.toReal(), line.height().toReal()));
+            }
+        }
+    }
+
+    QPen pen = p->pen();
+    {
+        QTextLineItemIterator iterator(eng, index, pos, selection);
         while (!iterator.atEnd()) {
             QScriptItem &si = iterator.next();
 
@@ -2689,18 +2720,8 @@ void QTextLine::draw_internal(QPainter *p, const QPointF &origPos,
                 format = formatCollection->defaultTextFormat();
 
             if (eng->hasFormats() || selection || formatCollection) {
-            format.merge(eng->format(&si));
+                prepareFormat(format, &si);
-
+                setPen(p, pen, format);
-            if (suppressColors) {
-                format.clearForeground();
-                format.clearBackground();
-                format.clearProperty(QTextFormat::TextUnderlineColor);
-            }
-            if (selection)
-                format.merge(selection->format);
-
-            setPenAndDrawBackground(p, pen, format, QRectF(iterator.x.toReal(), (y - lineBase).toReal(),
-                                                           iterator.itemWidth.toReal(), line.height().toReal()));
 
                 const qreal baseLineOffset = format.baselineOffset() / 100.0;
                 QTextCharFormat::VerticalAlignment valign = format.verticalAlignment();
@@ -2851,6 +2872,7 @@ void QTextLine::draw_internal(QPainter *p, const QPointF &origPos,
                 p->setFont(oldFont);
             }
         }
+    }
     eng->drawDecorations(p);
 
     if (xlateToFixedRange)

tests/baseline/text/tst_baseline_text.cpp

@@ -17,6 +17,7 @@ public:
 private slots:
     void tst_render_data();
     void tst_render();
+    void tst_differentScriptsBackgrounds();
 
 private:
     QDir htmlDir;
@@ -81,6 +82,26 @@ void tst_Text::tst_render()
     QBASELINE_TEST(image);
 }
 
+void tst_Text::tst_differentScriptsBackgrounds()
+{
+    QTextDocument textDocument;
+    textDocument.setPageSize(QSizeF(800, 600));
+    textDocument.setHtml(QString::fromUtf8("<i><font style=\"font-size:72px\"><font style=\"background:#FFFF00\">イ雨ｴ</font></font></i>"));
+
+    QImage image(800, 600, QImage::Format_ARGB32);
+    image.fill(Qt::white);
+
+    {
+        QPainter painter(&image);
+
+        QAbstractTextDocumentLayout::PaintContext context;
+        context.palette.setColor(QPalette::Text, Qt::black);
+        textDocument.documentLayout()->draw(&painter, context);
+    }
+
+    QBASELINE_CHECK(image, "tst_differentScriptsBackgrounds");
+}
+
 
 #define main _realmain
 QTEST_MAIN(tst_Text)