Fix breaking on fixed column width when text has tabs

When a text in QTextLayout contained tabs, these would be counted as
single glyphs when breaking the text on a fixed number of columns,
rather than the number of characters they span.

The patch calculates the number of characters represented by a tab by
using the average character width of the font engine.

Task-number: QTBUG-4468
Reviewed-by: Simon Hausmann

2 files changed, 43 insertions, 2 deletions

diff --git a/src/gui/text/qtextlayout.cpp b/src/gui/text/qtextlayout.cpp
index f8b0cbc..39a8bb8 100644
--- a/src/gui/text/qtextlayout.cpp
+++ b/src/gui/text/qtextlayout.cpp
@@ -1720,10 +1720,15 @@ void QTextLine::layout_helper(int maxGlyphs)
                 goto found;
 
             QFixed x = line.x + line.textWidth + lbh.tmpData.textWidth + lbh.spaceData.textWidth;
-            lbh.spaceData.textWidth += eng->calculateTabWidth(item, x);
+            QFixed tabWidth = eng->calculateTabWidth(item, x);
+
+            lbh.spaceData.textWidth += tabWidth;
             lbh.spaceData.length++;
             newItem = item + 1;
-            ++lbh.glyphCount;
+
+            QFixed averageCharWidth = eng->fontEngine(current)->averageCharWidth();
+            lbh.glyphCount += qRound(tabWidth / averageCharWidth);
+
             if (lbh.checkFullOtherwiseExtend(line))
                 goto found;
         } else if (current.analysis.flags == QScriptAnalysis::LineOrParagraphSeparator) {
diff --git a/tests/auto/qtextlayout/tst_qtextlayout.cpp b/tests/auto/qtextlayout/tst_qtextlayout.cpp
index 9f23ece..5ccae94 100644
--- a/tests/auto/qtextlayout/tst_qtextlayout.cpp
+++ b/tests/auto/qtextlayout/tst_qtextlayout.cpp
@@ -109,6 +109,7 @@ private slots:
     void capitalization_capitalize();
     void longText();
     void widthOfTabs();
+    void columnWrapWithTabs();
 
     // QTextLine stuff
     void setNumColumnsWrapAtWordBoundaryOrAnywhere();
@@ -1275,5 +1276,40 @@ void tst_QTextLayout::widthOfTabs()
     QCOMPARE(qRound(engine.width(0, 5)), qRound(engine.boundingBox(0, 5).width));
 }
 
+void tst_QTextLayout::columnWrapWithTabs()
+{
+    QTextLayout textLayout;
+    {
+        QTextOption textOption;
+        textOption.setWrapMode(QTextOption::WordWrap);
+        textLayout.setTextOption(textOption);
+    }
+
+    // Make sure string with spaces does not break
+    {
+        QString text = "Foo bar foo bar foo bar";
+        textLayout.setText(text);
+
+        textLayout.beginLayout();
+        QTextLine line = textLayout.createLine();
+        line.setNumColumns(30);
+        QCOMPARE(line.textLength(), text.length());
+        textLayout.endLayout();
+    }
+
+    // Make sure string with tabs breaks
+    {
+        QString text = "Foo\tbar\tfoo\tbar\tfoo\tbar";
+        textLayout.setText(text);
+        textLayout.beginLayout();
+        QTextLine line = textLayout.createLine();
+        line.setNumColumns(30);
+        QVERIFY(line.textLength() < text.length());
+        textLayout.endLayout();
+    }
+
+}
+
+
 QTEST_MAIN(tst_QTextLayout)
 #include "tst_qtextlayout.moc"