QGraphicsView and QGraphicsScene speeds

[jnk5y]

Ok I have a dialog with a QGraphicsView inside.
In my header i have QGraphicsScene *SampleScene;

SampleScene = new QGraphicsScene;
 
query.exec( "SELECT x,y FROM samples;" );
 
 while( query.next() )
 {
      QGraphicsItem *item = new QGraphicsRectItem ( 
        ( minX - query.value(0).toDouble() ) * -scaleX, ( maxY - query.value(1).toDouble() ) *  scaleY, 5, 5 );
 
      SampleScene->addItem(item);
 }
 
ui.graphicsView->setRenderHints( QPainter::Antialiasing );
ui.graphicsView->setScene(SampleScene);

SampleScene = new QGraphicsScene;

query.exec( "SELECT x,y FROM samples;" );

 while( query.next() )
 {
      QGraphicsItem *item = new QGraphicsRectItem ( 
        ( minX - query.value(0).toDouble() ) * -scaleX, ( maxY - query.value(1).toDouble() ) *  scaleY, 5, 5 );

      SampleScene->addItem(item);
 }

ui.graphicsView->setRenderHints( QPainter::Antialiasing );
ui.graphicsView->setScene(SampleScene);

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I would prefer dots rather than squares and should be easier to draw. I have tried ui.graphicsView->setUpdatesEnabled(false) which helped slightly but still is very slow. I have also tried QGraphicItemsGroup which I have yet to get working for some reason. I would put the items into a QList of QGraphicItems and then

SampleGroup = SampleScene->createItemGroup ( list );
SampleGroup->show();

SampleGroup = SampleScene->createItemGroup ( list );
SampleGroup->show();

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But I could never see the points. I have studied the 40000 chips example and have also implemented a custom QGraphicsItem which helped slightly in speed. Everything else looks similar to the chips example but much slower.