There's this code running after diagram.Bounds changes:

if (ScrollX < bounds.Left || ScrollX > bounds.Right)
     ScrollX = bounds.Left;
// similar for Y

Is the new Bounds rectangle top-left position equal to -18,-18?

I am trying to solve this problem in a different way and that is not working either. What happens is that after I add nodes and resize the diagram, the ScrollViewer around the diagram is in the correct position (let's say Y = 400) and even the region in the overview window is drawn in the correct position. But there is a mismatch between the ScrollViewer's position and the diagram ScrollY position. I can see this using the following code on the overview's mouse down event:

private void DiagramOverview_PreviewMouseDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
{
    ScrollViewer viewer = (ScrollViewer)DiagramOverview.Document.Parent;
    Console.WriteLine(viewer.VerticalOffset);
    Console.WriteLine(DiagramOverview.Document.ScrollY);
} 

And in the console, I see that the ScrollViewer Y position is 400, but the diagram ScrollY reports 0. This causes a sudden snap as soon as I begin to drag the mouse around the overview because the overview overrides the ScrollViewer. I attempted to manually synchronize the two by adding this line in the same event handler:

    DiagramOverview.Document.ScrollY = viewer.VerticalOffset; 

But this still causes the overview window to override the ScrollViewer. I want it the other way around. Any ideas how to synchronize them?

Thanks so much for looking into it.

That makes perfect sense about HorizontalOffset not necessarily matching ScrollX.

I added the ScrollTo command after ResizeToFit, but that still did not synchronize the overview window.  However, I played around and found that if I set ovw.FitAll = false and then ovw.FitAll = true after the ResizeToFit, it fixed the problem.  Something in there must have forced a sync.

Thanks again for your help.

Hi Stoyan,

Sorry to keep bothering you but I have one additional piece of the puzzle here.

I am using DiagramNodeAdapters throughout my diagram and they wrap a user control that has a scroll viewer in it.  I noticed that whenever I scroll the viewer inside the user control, the diagram scroll is affected but the scroll viewer around the diagram does not move!  I think this is the root of all of the problems I am having.  Any idea why this is happening?

Thanks,
Ben

That's what I think is happening. Here is all that I am doing:

1) Add a node with a TextBlock inside of a ScrollViewer inside the node.
2) Use the scroll the TextBlock up and down by clicking the arrows or using the scroll wheel.
3) Nothing appears to have changed but then when I click the Overview, it snaps the diagram back to 0,0 instantly upon dragging.

Removing the ScrollViewer from the node not only fixes this problem, but all of the other problems I was having as well. Even just adding the node to the diagram would reset the Overview back to 0, 0 in this way.

Thanks!  It's nice to have finally tracked this down.