2 files changed, 13 insertions, 3 deletions
diff --git a/src/printsupport/kernel/qpaintengine_alpha.cpp b/src/printsupport/kernel/qpaintengine_alpha.cpp
index 710691453a..0ae9464b69 100644
--- a/src/printsupport/kernel/qpaintengine_alpha.cpp
+++ b/src/printsupport/kernel/qpaintengine_alpha.cpp
@@ -376,6 +376,7 @@ QAlphaPaintEnginePrivate::QAlphaPaintEnginePrivate()
         m_pic(0),
         m_picengine(0),
         m_picpainter(0),
+        m_numberOfCachedRects(0),
         m_hasalpha(false),
         m_alphaPen(false),
         m_alphaBrush(false),
@@ -426,7 +427,14 @@ void QAlphaPaintEnginePrivate::addAlphaRect(const QRectF &rect)
 
 bool QAlphaPaintEnginePrivate::canSeeTroughBackground(bool somethingInRectHasAlpha, const QRectF &rect) const
 {
-    return somethingInRectHasAlpha && m_dirtyrgn.intersects(rect.toAlignedRect());
+    if (somethingInRectHasAlpha) {
+        if (m_dirtyRects.count() != m_numberOfCachedRects) {
+            m_cachedDirtyRgn.setRects(m_dirtyRects.constData(), m_dirtyRects.count());
+            m_numberOfCachedRects = m_dirtyRects.count();
+        }
+        return m_cachedDirtyRgn.intersects(rect.toAlignedRect());
+    }
+    return false;
 }
 
 void QAlphaPaintEnginePrivate::drawAlphaImage(const QRectF &rect)
diff --git a/src/printsupport/kernel/qpaintengine_alpha_p.h b/src/printsupport/kernel/qpaintengine_alpha_p.h
index 2becad7379..49a9938e56 100644
--- a/src/printsupport/kernel/qpaintengine_alpha_p.h
+++ b/src/printsupport/kernel/qpaintengine_alpha_p.h
@@ -99,7 +99,9 @@ public:
 
     QRegion m_alphargn;
     QRegion m_cliprgn;
-    QRegion m_dirtyrgn;
+    mutable QRegion m_cachedDirtyRgn;
+    mutable int m_numberOfCachedRects;
+    QVector<QRect> m_dirtyRects;
 
     bool m_hasalpha;
     bool m_alphaPen;
@@ -115,7 +117,7 @@ public:
     QPen m_pen;
 
     void addAlphaRect(const QRectF &rect);
-    void addDirtyRect(const QRectF &rect) { m_dirtyrgn |= rect.toAlignedRect(); }
+    void addDirtyRect(const QRectF &rect) { m_dirtyRects.append(rect.toAlignedRect()); }
     bool canSeeTroughBackground(bool somethingInRectHasAlpha, const QRectF &rect) const;
 
     QRectF addPenWidth(const QPainterPath &path);