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All DiagramItem-inherited objects you add to the diagram become a part of the WPF visual tree. If you want to add and remove items dynamically so that only ones inside current viewport exist in the visual tree, you will end up with something similar to what the VirtualizingDiagram control does, so check if it will work for you.

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GetNodesInViewport returns nodes from Diagram.Nodes collection that intersect with current viewport. You could implement some kind of virtualization yourself if you enable the RemoveHiddenItemsFromVisualTree property, and then each time scroll position changes set Visible = true for all items in the viewport, and Visible = false for all items outside of it.

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The diagram with all of its child elements is part of the WPF visual tree.

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I suppose you could keep items detached from the diagram and only add them when their bounding rectangle intersects current viewport, or instead of DiagramNode and DiagramLink objects keep information in separate model data objects. Again, that's what VirtualizingDiagram already does out of the box; check the Virtualization sample project for an example of how it works.

I hope that helps,
Stoyan

I am trying VirtualizingDiagram. Got questions:
1. use out of box VirtualizingDiagram, Do I suppose to only see nodes and links in the viewport? I attached an image from snoop to capture the diagram, the visible viewport is the rectangle on the left, I was hoping only see nodes in that rectangle.
2. I am not be able to find RemoveHiddenItemsFromVisualTree property. Is it in VirtualizingDiagram class?

Thanks,

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You might be seeing more nodes if this tool intercepts the layout process and passes a larger arrange size to the diagram. If it just shows all current children of a control in a separate view, you can still see nodes outside of the viewport because they are not reused until number of elements reaches VisualCacheSize.

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I think it's available since the v3.1 release, try upgrading to latest version.

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It doesn't seem the control expects actual ShapeNode and DiagramLink data objects, and for example it looks for X,Y properties in data items instead of Bounds. It should still be possible to use actual nodes and links as items, try setting node positions from ResolveNodePosition callback, and copying or binding other properties from InstantiateNode and InstantiateLink callbacks.

I hope that helps,
Stoyan