how to move several plot items relatively to mouse movement

I have got the following problem:
If I drag only one item, then in "cursorMoved" function, I just set the mouseposition to the item's position and it works fine. If I select several items and want to drag them, then they get all the mouse position and appears at the same place. How can I implement such movement that the selected items only moves relatively to mouse direction and movement? Can you provide me a code snippet of it? I thought about storing the initial mouse click position and calculate the difference relatively to this initial point, but the "cursorMoved" function is called frequently while dragging so that this varaible would be overridden...

my code:

Code:

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...
// create QwtPlotPicker to allow user moving the points on the plot
 
    	    picker = new QwtPlotPicker(QwtPlot::xBottom, QwtPlot::yLeft,
    	    		QwtPicker::RectSelection | QwtPicker::DragSelection,
				QwtPlotPicker::RectRubberBand, QwtPicker::AlwaysOn,
				this->canvas());
 
   // connect the signals coming from QwtPlotPicker with the member functions
    	    connect( picker, SIGNAL(moved(const QwtDoublePoint& ) ),
    	    		this, SLOT(cursorMoved( const QwtDoublePoint& ) ) );
 
    	    connect( picker, SIGNAL(selected (const QwtDoubleRect &) ),
    	       	    		this, SLOT(RectangleSelected( const QwtDoubleRect& ) ) );
...
 
// this function provides the ability to select several items on the plot by dragging a rectangle around them
void Plot::RectangleSelected( const QwtDoubleRect& rect){
	std::cout << "in Plot::RectangleSelected" << std::endl;
	//============= clear the list with selected items, before start new selection
	  if(!selected_Points.empty()){
		while(!selected_Points.empty()){
			QwtPlotMarker *tempMark = selected_Points.back();
			const QwtSymbol symbol = tempMark->symbol();
			 QwtSymbol newSymbol = symbol;
			 newSymbol.setBrush(symbol.brush().color().light(150));	// turn back the highlighten symbol
			 tempMark->setSymbol(newSymbol);
			selected_Points.pop_back();		// delete the selected items from the list
		}
	}
	  //============= end of clear the list
 
	const QwtPlotItemList& List = itemList();		// get all items from the plot
		QwtPlotItemIterator Iter = List.begin();
 
		// get the two vertice of the selection rectangle
			QwtDoublePoint tl = rect.topLeft();
			QwtDoublePoint br = rect.bottomRight();
			std::cout << "recOfClick(x,y,width, height) ="  << rect.x()<<", " << rect.y() << ", " << rect.width()<< ", "<<rect.height()<< std::endl;
		 double TRtlX = this->transform(picker->xAxis(),tl.x());		// transform the rectangles coordinates to plot's coordinates
		 double TRtlY = this->transform(picker->yAxis(),tl.y());
		 double TRbrX = this->transform(picker->xAxis(),br.x());
		 double TRbrY= this->transform(picker->yAxis(),br.y());
		 QwtDoubleRect *trRect= new QwtDoubleRect(QRect(QPoint(TRtlX,TRtlY),QPoint(TRbrX,TRbrY)));	// build a rectangle with the new coordinates
		 std::cout << "recOfClick(x,y,width, height) ="  << trRect->x()<<", " << trRect->y() << ", " << trRect->width()<< ", "<<trRect->height()<< std::endl;
		 if( trRect->width()<5 && trRect->height()<5){ // if it was just a click and not drugged rectangle, then...
			 trRect->setHeight(20);		// ...generate a rectangle around the click's position
			 trRect->setWidth(20);
 
		 }
 
	  while(Iter != List.end())			// and iterate through them...
	  {
	     if((*Iter)->rtti() == QwtPlotItem::Rtti_PlotMarker){	// ... until you find the item from class QwtPLotMarker
	    	 QwtPlotMarker *mark = ((QwtPlotMarker*)(*Iter));
				 double x = this->transform(mark->xAxis(),mark->xValue());		// transform the item's coordinates to plot's coordinates
	    	     double y = this->transform(mark->yAxis(),mark->yValue());
	    	      	std::cout << "mark.xValue()=" << mark->xValue() << ", mark.yValue()=" << mark->yValue()<< std::endl;
	    	      	std::cout << "transformed mark coord = " << x << ", " << y<< std::endl;
	    	      	QwtDoublePoint trPoint = QwtDoublePoint(x,y);		// create a point consisting of transformed coordinates
 
 
	    	  if(trRect->contains(trPoint)){			// if click's rectangle includes the QwtPlotMarker, then...
	        	std::cout << "MATCH"  << std::endl;
 
				 //selectedPoint = mark;					// ... save the pointer to this item into variable "selectedPoint"
				 std::cout << "selectedPoint = " << mark << std::endl;
				 const QwtSymbol symbol = mark->symbol();
				 QwtSymbol newSymbol = symbol;
				 newSymbol.setBrush(symbol.brush().color().dark(150));	// highlighten the selected item by darken its color
				 mark->setSymbol(newSymbol);
	        	selected_Points.push_back(mark);
	        }
 
	     }
	     Iter++;
	  }
		 replot();
		 std::cout << "selected_Points.size()= " << selected_Points.size() << std::endl;
}
//##################################################################
// this function provides the ability to move items on the plot
void Plot::cursorMoved( const QwtDoublePoint& Point){
 
	std::cout << "in Plot::cursorMoved " <<  std::endl;
	std::cout << "Point.x()= " << Point.x() <<"Point.y()= " << Point.y() << std::endl;
	if(!selected_Points.empty()){		//if the list with selected items is not empty, then...
		for(unsigned i=0; i< selected_Points.size(); ++i) {
			 std::cout << "loop " << i << std::endl;
			selected_Points[i]->setValue(Point);	// set the new coordinates to the moved item
				    	}
		this->replot();	// replot the plot widget after the selected point was moved

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Quote:

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Originally Posted by rambo83

I have got the following problem:
... I thought about storing the initial mouse click position and calculate the difference relatively to this initial point ...

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You've got it.
A way to do what you want is to store the coordinates of the mouse click then computed in mouse move the offset that you need to apply for your selected vertices in your cursorMove method.

ok, I have solved it by storing the center point of selection rectangle as a reference point and calculated then in "cursorMoved()" the offset and set then the new values by

Code:

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setValue(old_marker_pos.x() + offset_x, old_marker_pos.y() + offset_y)

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It has somehow still strange behaviour. I think I have to calculate the intermediate point between the selected items to have better behaviour or do you have another idea?

I can't understand what kind of strange behaviour you are talking about. Please details what's going on.

Moving vertices means dragging, doesn't it? So you need to store the coordinates when starting dragging. Why the center of the selected rect?

Another point: be aware of coordinate system between mouse (eg pixel) and graph(point) when computing the offset.

with "strange behaviour" I mean, that the selected points spring to the starting point of dragging and only then follow the mouse movement. I think it is due to the center rectangle point as reference, because if I start to drag in the middle of selected area (rectangle) then everything is ok (expected behaviour), but if I start to drag from other place of selected area, then the selected point spring there (strange behaviour) and after that follow normaly the mouse.

So which point shall be the reference point?

In fact, selecting point is different from dragging ones. You first select vertices, then you drag them.

So, your strange behaviour is due to difference between the center of your selected rect and the point when you strat to drag. Vertices seems to "jump" because when you start to drag, the offset is computed from the center of the rect and you didn't move vertices before.

So computing the offset from the starting point when starting to drag might be ok.