4 files changed, 11 insertions, 7 deletions
diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index 067a630d4d..5c6c8d186a 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -179,6 +179,7 @@ QFontEngine::QFontEngine()
 
     hbFace = 0;
     glyphFormat = -1;
+    m_subPixelPositionCount = 0;
 }
 
 QFontEngine::~QFontEngine()
@@ -635,17 +636,19 @@ QImage QFontEngine::alphaRGBMapForGlyph(glyph_t glyph, QFixed /*subPixelPosition
     return rgbMask;
 }
 
-QFixed QFontEngine::subPixelPositionForX(QFixed x)
+QFixed QFontEngine::subPixelPositionForX(QFixed x) const
 {
-    int m_subPixelPositionCount = 4;
-    if (!supportsSubPixelPositions())
-        return 0;
+    if (m_subPixelPositionCount <= 1 || !supportsSubPixelPositions())
+        return QFixed();
 
     QFixed subPixelPosition;
     if (x != 0) {
         subPixelPosition = x - x.floor();
         QFixed fraction = (subPixelPosition / QFixed::fromReal(1.0 / m_subPixelPositionCount)).floor();
-        subPixelPosition = fraction / QFixed(m_subPixelPositionCount);
+
+        // Compensate for precision loss in fixed point to make sure we are always drawing at a subpixel position over
+        // the lower boundary for the selected rasterization by adding 1/64.
+        subPixelPosition = fraction / QFixed(m_subPixelPositionCount) + QFixed::fromReal(0.015625);
     }
     return subPixelPosition;
 }
diff --git a/src/gui/text/qfontengine_ft.cpp b/src/gui/text/qfontengine_ft.cpp
index eb7415ae8e..6845c67463 100644
--- a/src/gui/text/qfontengine_ft.cpp
+++ b/src/gui/text/qfontengine_ft.cpp
@@ -657,6 +657,7 @@ QFontEngineFT::QFontEngineFT(const QFontDef &fd)
     defaultFormat = Format_None;
     embeddedbitmap = false;
     cacheEnabled = qgetenv("QT_NO_FT_CACHE").isEmpty() || qgetenv("QT_NO_FT_CACHE").toInt() == 0;
+    m_subPixelPositionCount = 4;
 }
 
 QFontEngineFT::~QFontEngineFT()
diff --git a/src/gui/text/qfontengine_ft_p.h b/src/gui/text/qfontengine_ft_p.h
index d4a6def286..fd0be4f1c8 100644
--- a/src/gui/text/qfontengine_ft_p.h
+++ b/src/gui/text/qfontengine_ft_p.h
@@ -315,7 +315,6 @@ private:
     bool initFromFontEngine(const QFontEngineFT *fontEngine);
 
     HintStyle defaultHintStyle() const { return default_hint_style; }
-
 protected:
 
     QFreetypeFace *freetype;
diff --git a/src/gui/text/qfontengine_p.h b/src/gui/text/qfontengine_p.h
index ec1f22b6e1..4caf91e735 100644
--- a/src/gui/text/qfontengine_p.h
+++ b/src/gui/text/qfontengine_p.h
@@ -158,7 +158,7 @@ public:
     };
     virtual int synthesized() const { return 0; }
     virtual bool supportsSubPixelPositions() const { return false; }
-    QFixed subPixelPositionForX(QFixed x);
+    virtual QFixed subPixelPositionForX(QFixed x) const;
 
     virtual QFixed emSquareSize() const { return ascent(); }
 
@@ -277,6 +277,7 @@ public:
 
     int glyphFormat;
     QImage currentlyLockedAlphaMap;
+    int m_subPixelPositionCount; // Number of positions within a single pixel for this cache
 
 protected:
     static const QVector<QRgb> &grayPalette();