Did anyone already think of having an intelligent zooming in and out that keeps either the selection or the visible nodes in mid of diagram when zooming?

i.e.

if this is the mid point to keep in center:

var mid = MiddlePnt(Selection.Nodes.Count >= 1 ?
Selection.Bounds :
GetContentBounds(false, true));

and

internal Point MiddlePnt(Rect r)
{
//arithmetic mid
return new Point((r.Right - r.Left)/2, (r.Bottom - r.Top)/2);
}

how to keep this mid point in center while doing e.g. Mousewheel zoomOut() or zoomIn()? (or over dedicated button functions). NB: zoomIn() and zoomOut() do not have an agrument for specifying the center point.

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It seems that the ScrollTo(mid) does not seem to work depending on size of diagram and/or scrollviewer positioning.

This seems to be a function that diagram might always need, so maybe there is a standard method or solution for this?

cheers

i think neither this function follows the pivot correctly if the diagram.bounds are not fully within the scrollviewer, i.e. probably i will have to enlarge diagram boundaries size prior to pivoting so that there is enough leeway... ?

(investigating)

i actually foun d& reused your code from and old 2009 post:

        public void SetZoom(double percentage)
        {
            ScrollViewer scrollViewer = (ScrollViewer)Parent;
            var diagramTransform = scrollViewer.TransformToVisual(DocumentPlane);

            // this point should remain centered when zooming in?
            Point scrollViewerCenter = new Point(
                scrollViewer.ActualWidth / 2, scrollViewer.ActualHeight / 2);
            Point weighPt = WeightMidPoint();

            Point diagramPointAtViewCenter = diagramTransform.Transform(weighPt); //weighPt scrollViewerCenter

            ZoomFactor = Math.Max(10, Math.Min(percentage, 200));

            Rect clientAreaSize = new Rect(0, 0, scrollViewer.ActualWidth, scrollViewer.ActualHeight);
            Rect clientAreaDiagSize = ClientToDoc(clientAreaSize);

            // ensure the diagram is always larger than the scrollviewer
            Rect newBounds = GetContentBounds(false, true);
            double diffX = Math.Max(0, clientAreaDiagSize.Width - newBounds.Width);
            double diffY = Math.Max(0, clientAreaDiagSize.Height - newBounds.Height);
            newBounds.Inflate(diffX / 2, diffY / 2);
            Bounds = newBounds;

            // make sure the diagram center is at the scrollviewer center
            ScrollX = diagramPointAtViewCenter.X - clientAreaDiagSize.Width / 2;
            ScrollY = diagramPointAtViewCenter.Y - clientAreaDiagSize.Height / 2;
        }

        //arithmetic mid
        internal Point MiddlePnt(Rect r)
        {
            return new Point((r.Right - r.Left)/2 + r.X, (r.Bottom - r.Top)/2 + r.Y);
        }

        //diagram weighted mid (selected or no)
        internal Point WeightMidPoint()
        {
            var mid = MiddlePnt(Selection.Nodes.Count >= 1 ?
                ClientToDoc(Selection.Bounds) :
                ClientToDoc(GetContentBounds(false, true)));
                //(Selection.Bounds) :
                //(GetContentBounds(false, true)));
            return mid;
        }
 

so now the behaviour uis better, but still when the user zooms too near, some spiralling happens

ok found the problem on the above code:

Point diagramPointAtViewCenter = diagramTransform.Transform(weighPt); //weighPt

should be:

Point diagramPointAtViewCenter = weighPt;

and then it pans after the selection well.

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solved