--- a/src/gui/effects/qgraphicseffect.cpp	Mon Mar 15 12:43:09 2010 +0200
+++ b/src/gui/effects/qgraphicseffect.cpp	Thu Apr 08 14:19:33 2010 +0300
@@ -699,12 +699,17 @@
     if (sourceIsPixmap()) {
         // No point in drawing in device coordinates (pixmap will be scaled anyways).
         const QPixmap pixmap = sourcePixmap(Qt::LogicalCoordinates, &offset, NoPad);
-        d->filter->draw(painter, offset, pixmap);
+        if (!pixmap.isNull())
+            d->filter->draw(painter, offset, pixmap);
+
         return;
     }
 
     // Draw pixmap in deviceCoordinates to avoid pixmap scaling.
     const QPixmap pixmap = sourcePixmap(Qt::DeviceCoordinates, &offset);
+    if (pixmap.isNull())
+        return;
+
     QTransform restoreTransform = painter->worldTransform();
     painter->setWorldTransform(QTransform());
     d->filter->draw(painter, offset, pixmap);
@@ -721,7 +726,8 @@
     elements. The level of detail can be modified using the setBlurRadius()
     function. Use setBlurHints() to choose the blur hints.
 
-    By default, the blur radius is 5 pixels.
+    By default, the blur radius is 5 pixels. The blur radius is specified in
+    device coordinates.
 
     \img graphicseffect-blur.png
 
@@ -776,6 +782,9 @@
     radius results in a more blurred appearance.
 
     By default, the blur radius is 5 pixels.
+
+    The radius is given in device coordinates, meaning it is
+    unaffected by scale.
 */
 qreal QGraphicsBlurEffect::blurRadius() const
 {
@@ -858,9 +867,11 @@
     if (painter->paintEngine()->type() == QPaintEngine::OpenGL2)
         mode = NoPad;
 
-    // Draw pixmap in device coordinates to avoid pixmap scaling.
     QPoint offset;
     QPixmap pixmap = sourcePixmap(Qt::LogicalCoordinates, &offset, mode);
+    if (pixmap.isNull())
+        return;
+
     d->filter->draw(painter, offset, pixmap);
 }
 
@@ -877,7 +888,8 @@
 
     By default, the drop shadow is a semi-transparent dark gray
     (QColor(63, 63, 63, 180)) shadow, blurred with a radius of 1 at an offset
-    of 8 pixels towards the lower right.
+    of 8 pixels towards the lower right. The drop shadow offset is specified
+    in device coordinates.
 
     \img graphicseffect-drop-shadow.png
 
@@ -906,6 +918,9 @@
 
     By default, the offset is 8 pixels towards the lower right.
 
+    The offset is given in device coordinates, which means it is
+    unaffected by scale.
+
     \sa xOffset(), yOffset(), blurRadius(), color()
 */
 QPointF QGraphicsDropShadowEffect::offset() const
@@ -1047,6 +1062,9 @@
     // Draw pixmap in device coordinates to avoid pixmap scaling.
     QPoint offset;
     const QPixmap pixmap = sourcePixmap(Qt::DeviceCoordinates, &offset, mode);
+    if (pixmap.isNull())
+        return;
+
     QTransform restoreTransform = painter->worldTransform();
     painter->setWorldTransform(QTransform());
     d->filter->draw(painter, offset, pixmap);