Hello @ everyone her,

I am currently implementing a representation of some measurement values in a 2d-plane.
There is a huge amount of items (one pixel long QLineF 's) in the scene (up to 1 million) and a few graphs consisting of about 100 - 200 QLineF ' s.

Qt Code: 
  1. bool myGraph::insertGraphIntoScene(QList <QPointF> &list, QColor col)
  2. {
  3. 	if(list.size() == 0)
  4. 		return false;
  5.  
  6. 	else if(list.size() <2)
  7. 	{
  8. 		if(myLineGroupGraph == NULL)
  9. 			myLineGroupGraph = new QGraphicsItemGroup();
  10.  
  11. 		QPointF p = list.at(0);
  12. 		QGraphicsLineItem * line = new QGraphicsLineItem(p.x(),p.y(),p.x(),p.y());
  13. 		line->setPen(col);
  14.  
  15. 		// get the line that crosses y-axis
  16. 		if(p.x() == center.x())
  17. 			lineThroughYAxis = line;
  18.  
  19.  
  20. 		myLineGroupGraph->addToGroup(line);
  21. 		scene.addItem(myLineGroupGraph);
  22. 	}
  23.  
  24. 	else
  25. 	{
  26. 		if(myLineGroupGraph == NULL)
  27. 			myLineGroupGraph = new QGraphicsItemGroup();
  28. 		int i = 0;
  29. 		QPointF p1,p2;
  31. 		while(list.size() > i+2)
  32. 		{
  33. 			p1 = list.at(i);
  34. 			p2 = list.at(i+1);
  35.  
  36. 			line = new QGraphicsLineItem(p1.x(),p1.y(),p2.x(),p2.y());
  37. 			line->setPen(col);
  38. 			myLineGroupGraph->addToGroup(line);
  39. 			i++;
  40. 		}
  41.  
  42. 		scene.addItem(myLineGroupGraph);
  43. 	}
  44. 	return true;
  45. }
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Now as seen in my code I have grouped all lines the curve consists of into myLineGroupGraph. Since I need to be able to click onto the curve and drag it up and down along the y axis, I am looking for a fast way to do so.

By calling

Qt Code: 
  1. myLineGroupGraph->moveBy(...,...);
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I can move the itemgroup up and down but it takes ages.

the viewportupdate is set to QGraphicsView::SmartViewportUpdate
I have tried QGraphicsView::FullViewportUpdate too.

Got any idea how to optimize implementation of the curve so the dragging gets faster?