Fix painting artifacts on text

The height of the row is not only decided by the maximum height of the
set of glyphs currently being added to the glyph cache, but also the
height of the glyphs previously added to the current line in the glyph
cache. To minimize the space used, we now calculate the maximum height
for glyphs per line, and use this as the vertical advancement when
positioning the next line in the cache. The change also removes a
redundant test ((c_x + c.w > c.h) is caught earlier on and will
always be false at this point.)

Task-number: QTBUG-9176
Reviewed-by: Trond

2 files changed, 7 insertions, 10 deletions

diff --git a/src/gui/painting/qtextureglyphcache.cpp b/src/gui/painting/qtextureglyphcache.cpp
index cf545be..9eda0ef 100644
--- a/src/gui/painting/qtextureglyphcache.cpp
+++ b/src/gui/painting/qtextureglyphcache.cpp
@@ -133,10 +133,13 @@ void QTextureGlyphCache::populate(QFontEngine *fontEngine, int numGlyphs, const
     while (iter != listItemCoordinates.end()) {
         Coord c = iter.value();
 
+        m_currentRowHeight = qMax(m_currentRowHeight, c.h + margin * 2);
+
         if (m_cx + c.w > m_w) {
             // no room on the current line, start new glyph strip
             m_cx = 0;
-            m_cy += rowHeight;
+            m_cy += m_currentRowHeight;
+            m_currentRowHeight = 0; // New row
         }
         if (m_cy + c.h > m_h) {
             int new_height = m_h*2;
@@ -153,14 +156,7 @@ void QTextureGlyphCache::populate(QFontEngine *fontEngine, int numGlyphs, const
         fillTexture(c, iter.key());
         coords.insert(iter.key(), c);
 
-        if (m_cx + c.w > m_w) {
-            m_cx = 0;
-            m_cy += rowHeight;
-        } else {
-            // for the Mono case, glyph_width is 8-bit aligned,
-            // and therefore so will m_cx
-            m_cx += c.w;
-        }
+        m_cx += c.w;
         ++iter;
     }
 
diff --git a/src/gui/painting/qtextureglyphcache_p.h b/src/gui/painting/qtextureglyphcache_p.h
index 803e71b..8c2f5b4 100644
--- a/src/gui/painting/qtextureglyphcache_p.h
+++ b/src/gui/painting/qtextureglyphcache_p.h
@@ -77,7 +77,7 @@ class Q_GUI_EXPORT QTextureGlyphCache : public QFontEngineGlyphCache
 public:
     QTextureGlyphCache(QFontEngineGlyphCache::Type type, const QTransform &matrix)
         : QFontEngineGlyphCache(matrix, type), m_current_fontengine(0),
-                                               m_w(0), m_h(0), m_cx(0), m_cy(0)
+                                               m_w(0), m_h(0), m_cx(0), m_cy(0), m_currentRowHeight(0)
         { }
 
     virtual ~QTextureGlyphCache() { }
@@ -120,6 +120,7 @@ protected:
     int m_h; // image height
     int m_cx; // current x
     int m_cy; // current y
+    int m_currentRowHeight; // Height of last row
 };