[FEATURE] Pan composer with middle mouse button

Zoom in and out on composer using mouse scroll wheel

src/core/composer/qgscomposeritem.cpp

@@ -924,6 +924,13 @@ void QgsComposerItem::setEffectsEnabled( bool effectsEnabled )
 
 void QgsComposerItem::hoverMoveEvent( QGraphicsSceneHoverEvent * event )
 {
+  if ( QgsApplication::mouseButtons() == Qt::MidButton )
+  {
+    //middle mouse button panning, make sure we use the closed hand cursor
+    setCursor( Qt::ClosedHandCursor );
+    return;
+  }
+
   if ( isSelected() )
   {
     setCursor( cursorForPosition( event->pos() ) );

src/gui/qgscomposerview.cpp

@@ -48,6 +48,7 @@ QgsComposerView::QgsComposerView( QWidget* parent, const char* name, Qt::WFlags
     , mPaintingEnabled( true )
     , mHorizontalRuler( 0 )
     , mVerticalRuler( 0 )
+    , mPanning( false )
 {
   Q_UNUSED( f );
   Q_UNUSED( name );
@@ -83,6 +84,15 @@ void QgsComposerView::mousePressEvent( QMouseEvent* e )
     }
     return;
   }
+  else if ( e->button() == Qt::MidButton )
+  {
+    //pan composer with middle button
+    mPanning = true;
+    mMouseLastXY = e->pos();
+    setCursor( Qt::ClosedHandCursor );
+    e->accept();
+    return;
+  }
 
   switch ( mCurrentTool )
   {
@@ -310,6 +320,15 @@ void QgsComposerView::mouseReleaseEvent( QMouseEvent* e )
 
   QPointF scenePoint = mapToScene( e->pos() );
 
+  if ( mPanning )
+  {
+    //panning with middle button
+    mPanning = false;
+    setCursor( Qt::ArrowCursor );
+    e->accept();
+    return;
+  }
+
   switch ( mCurrentTool )
   {
     case Select:
@@ -430,6 +449,15 @@ void QgsComposerView::mouseMoveEvent( QMouseEvent* e )
       QGraphicsView::mouseMoveEvent( e );
     }
   }
+  else if ( mPanning )
+  {
+    //panning with middle mouse button, scroll view
+    horizontalScrollBar()->setValue( horizontalScrollBar()->value() - ( e->x() - mMouseLastXY.x() ) );
+    verticalScrollBar()->setValue( verticalScrollBar()->value() - ( e->y() - mMouseLastXY.y() ) );
+    mMouseLastXY = e->pos();
+    e->accept();
+    return;
+  }
   else
   {
     QPointF scenePoint = mapToScene( e->pos() );
@@ -757,16 +785,47 @@ void QgsComposerView::wheelEvent( QWheelEvent* event )
 {
   QPointF scenePoint = mapToScene( event->pos() );
 
-  //select topmost item at position of event
-  QgsComposerItem* theItem = composition()->composerItemAt( scenePoint );
-  if ( theItem )
+  if ( currentTool() == MoveItemContent )
   {
-    if ( theItem->isSelected() )
+    //move item content tool, so scroll events get handled by the composer item
+
+    //select topmost item at position of event
+    QgsComposerItem* theItem = composition()->composerItemAt( scenePoint );
+    if ( theItem )
     {
-      QPointF itemPoint = theItem->mapFromScene( scenePoint );
-      theItem->beginCommand( tr( "Zoom item content" ) );
-      theItem->zoomContent( event->delta(), itemPoint.x(), itemPoint.y() );
-      theItem->endCommand();
+      if ( theItem->isSelected() )
+      {
+        QPointF itemPoint = theItem->mapFromScene( scenePoint );
+        theItem->beginCommand( tr( "Zoom item content" ) );
+        theItem->zoomContent( event->delta(), itemPoint.x(), itemPoint.y() );
+        theItem->endCommand();
+      }
+    }
+  }
+  else
+  {
+    //zoom whole composition
+    if ( event->delta() > 0 )
+    {
+      scale( 2, 2 );
+    }
+    else
+    {
+      scale( 0.5, 0.5 );
+    }
+
+    updateRulers();
+    update();
+    //redraw cached map items
+    QList<QGraphicsItem *> itemList = composition()->items();
+    QList<QGraphicsItem *>::iterator itemIt = itemList.begin();
+    for ( ; itemIt != itemList.end(); ++itemIt )
+    {
+      QgsComposerMap* mypItem = dynamic_cast<QgsComposerMap *>( *itemIt );
+      if (( mypItem ) && ( mypItem->previewMode() == QgsComposerMap::Render ) )
+      {
+        mypItem->updateCachedImage();
+      }
     }
   }
 }

src/gui/qgscomposerview.h

@@ -167,6 +167,9 @@ class GUI_EXPORT QgsComposerView: public QGraphicsView
     /** Draw a shape on the canvas */
     void addShape( Tool currentTool );
 
+    bool mPanning;
+    QPoint mMouseLastXY;
+
     //void connectAddRemoveCommandSignals( QgsAddRemoveItemCommand* c );
 
   signals: