Fix alignment of text with negative right bearing

In change 5364fd96a72c89b281f0540da909fe64d0575ccf and some related
changes, we made sure that the natural text width used for calculating
bounding rects and line breaks in the text, takes the right bearing
of the last glyph into consideration.

As a side-effect, this broke alignment of text, as we want to align
based on the accumulated advance of the glyphs, not based on the actual
width. This is in particular important when aligning monospaced text,
since the text can become misaligned if the glyphs extend beyond their
advance. The bug was visible e.g. in line numbers ending with 2 in
Qt Creator on X11, which would be shifted one pixel to the left compared
to other line numbers.

Task-number: QTBUG-8864
Reviewed-by: Thorbjørn

3 files changed, 6 insertions, 2 deletions

diff --git a/src/gui/painting/qpainter.cpp b/src/gui/painting/qpainter.cpp
index dc96c17..9e2fc82 100644
--- a/src/gui/painting/qpainter.cpp
+++ b/src/gui/painting/qpainter.cpp
@@ -7994,10 +7994,11 @@ start_lengthVariant:
         for (int i = 0; i < textLayout.lineCount(); i++) {
             QTextLine line = textLayout.lineAt(i);
 
+            qreal advance = textLayout.engine()->lines[i].textAdvance.toReal();
             if (tf & Qt::AlignRight)
-                xoff = r.width() - line.naturalTextWidth();
+                xoff = r.width() - advance;
             else if (tf & Qt::AlignHCenter)
-                xoff = (r.width() - line.naturalTextWidth())/2;
+                xoff = (r.width() - advance)/2;
 
             line.draw(painter, QPointF(r.x() + xoff + line.x(), r.y() + yoff));
         }
diff --git a/src/gui/text/qtextengine_p.h b/src/gui/text/qtextengine_p.h
index f36cbd2..5054b66 100644
--- a/src/gui/text/qtextengine_p.h
+++ b/src/gui/text/qtextengine_p.h
@@ -382,6 +382,7 @@ struct Q_AUTOTEST_EXPORT QScriptLine
     QFixed y;
     QFixed width;
     QFixed textWidth;
+    QFixed textAdvance;
     int from;
     signed int length : 29;
     mutable uint justified : 1;
diff --git a/src/gui/text/qtextlayout.cpp b/src/gui/text/qtextlayout.cpp
index af91603..cc6793d 100644
--- a/src/gui/text/qtextlayout.cpp
+++ b/src/gui/text/qtextlayout.cpp
@@ -1875,6 +1875,7 @@ void QTextLine::layout_helper(int maxGlyphs)
                     line.textWidth += lbh.softHyphenWidth;
                 }
 
+                line.textAdvance = line.textWidth;
                 line.textWidth += lbh.rightBearing;
 
                 goto found;
@@ -1885,6 +1886,7 @@ void QTextLine::layout_helper(int maxGlyphs)
     }
     LB_DEBUG("reached end of line");
     lbh.checkFullOtherwiseExtend(line);
+    line.textAdvance = line.textWidth;
     line.textWidth += lbh.rightBearing;
 
 found: