Add a little debug output to make clear the source of the QPaintEngine

error


git-svn-id: http://svn.osgeo.org/qgis/trunk/qgis@5068 c8812cc2-4d05-0410-92ff-de0c093fc19c

src/gui/qgsmaprender.cpp

@@ -205,6 +205,15 @@ void QgsMapRender::render(QPainter* painter)
     std::cout << "QgsMapRender::render: at layer item '" << (*li).toLocal8Bit().data() << "'." << std::endl;
 #endif
 
+    // This call is supposed to cause the progress bar to
+    // advance. However, it seems that updating the progress bar is
+    // incompatible with having a QPainter active (the one that is
+    // passed into this function), as Qt produces a number of errors
+    // when try to do so. I'm (Gavin) not sure how to fix this, but
+    // added these comments and debug statement to help others...
+    std::cerr << "If there is a QPaintEngine here, it is caused by an emit "
+      "call just after line " << __LINE__ << " in file " << __FILE__ << ".\n";
+
     emit setProgress(myRenderCounter++,layers.size());
     QgsMapLayer *ml = QgsMapLayerRegistry::instance()->mapLayer(*li);