Possible fix for slow loading projects when the project contains

print compositions and there is network issues with connections
to installed printers. (workaround QTBUG-3033)

(refs #12234)

cherry-picked from 06732f1

Author: nyalldawson

src/app/composer/qgscomposer.cpp

@@ -105,6 +105,7 @@ QgsComposer::QgsComposer( QgisApp *qgis, const QString& title )
     : QMainWindow()
     , mTitle( title )
     , mQgis( qgis )
+    , mPrinter( 0 )
     , mUndoView( 0 )
     , mAtlasFeatureAction( 0 )
 {
@@ -645,6 +646,7 @@ QgsComposer::QgsComposer( QgisApp *qgis, const QString& title )
 QgsComposer::~QgsComposer()
 {
   deleteItemWidgets();
+  delete mPrinter;
 }
 
 void QgsComposer::setupTheme()
@@ -1701,7 +1703,7 @@ void QgsComposer::printComposition( QgsComposer::OutputMode mode )
   }
 
   //orientation and page size are already set to QPrinter in the page setup dialog
-  QPrintDialog printDialog( &mPrinter, 0 );
+  QPrintDialog printDialog( printer(), 0 );
   if ( printDialog.exec() != QDialog::Accepted )
   {
     return;
@@ -1713,15 +1715,15 @@ void QgsComposer::printComposition( QgsComposer::OutputMode mode )
   QgsAtlasComposition* atlasMap = &mComposition->atlasComposition();
   if ( mode == QgsComposer::Single )
   {
-    mComposition->print( mPrinter, true );
+    mComposition->print( *printer(), true );
   }
   else
   {
     //prepare for first feature, so that we know paper size to begin with
     atlasMap->prepareForFeature( 0 );
 
-    mComposition->beginPrint( mPrinter, true );
-    QPainter painter( &mPrinter );
+    mComposition->beginPrint( *printer(), true );
+    QPainter painter( printer() );
 
     loadAtlasPredefinedScalesFromProject();
     if ( ! atlasMap->beginRender() && !atlasMap->featureFilterErrorString().isEmpty() )
@@ -1759,7 +1761,7 @@ void QgsComposer::printComposition( QgsComposer::OutputMode mode )
       }
 
       //start print on a new page if we're not on the first feature
-      mComposition->doPrint( mPrinter, painter, i > 0 );
+      mComposition->doPrint( *printer(), painter, i > 0 );
     }
     atlasMap->endRender();
     painter.end();
@@ -3556,7 +3558,7 @@ void QgsComposer::on_mActionPageSetup_triggered()
     return;
   }
 
-  QPageSetupDialog pageSetupDialog( &mPrinter, this );
+  QPageSetupDialog pageSetupDialog( printer(), this );
   pageSetupDialog.exec();
 }
 
@@ -3726,11 +3728,11 @@ void QgsComposer::setPrinterPageOrientation( QString orientation )
 {
   if ( orientation == tr( "Landscape" ) )
   {
-    mPrinter.setOrientation( QPrinter::Landscape );
+    printer()->setOrientation( QPrinter::Landscape );
   }
   else
   {
-    mPrinter.setOrientation( QPrinter::Portrait );
+    printer()->setOrientation( QPrinter::Portrait );
   }
 }
 
@@ -3742,11 +3744,11 @@ void QgsComposer::setPrinterPageDefaults()
   //set printer page orientation
   if ( paperWidth > paperHeight )
   {
-    mPrinter.setOrientation( QPrinter::Landscape );
+    printer()->setOrientation( QPrinter::Landscape );
   }
   else
   {
-    mPrinter.setOrientation( QPrinter::Portrait );
+    printer()->setOrientation( QPrinter::Portrait );
   }
 }
 
@@ -3799,3 +3801,13 @@ void QgsComposer::loadAtlasPredefinedScalesFromProject()
   atlasMap.setPredefinedScales( pScales );
 }
 
+QPrinter *QgsComposer::printer()
+{
+  //only create the printer on demand - creating a printer object can be very slow
+  //due to QTBUG-3033
+  if ( !mPrinter )
+    mPrinter = new QPrinter();
+
+  return mPrinter;
+}
+

src/app/composer/qgscomposer.h

@@ -19,7 +19,6 @@
 #include "ui_qgscomposerbase.h"
 #include "qgscomposermap.h"
 #include "qgscontexthelp.h"
-#include <QPrinter>
 #include <QDockWidget>
 
 class QgisApp;
@@ -509,6 +508,8 @@ class QgsComposer: public QMainWindow, private Ui::QgsComposerBase
     //! Load predefined scales from the project's properties
     void loadAtlasPredefinedScalesFromProject();
 
+    QPrinter* printer();
+
     /**Composer title*/
     QString mTitle;
 
@@ -558,7 +559,7 @@ class QgsComposer: public QMainWindow, private Ui::QgsComposerBase
     QAction *mActionPaste;
 
     //! Page & Printer Setup
-    QPrinter mPrinter;
+    QPrinter* mPrinter;
 
     QUndoView* mUndoView;