This is a bit difficult to explain, but here goes ...

When zooming in on the diagram using the opposite of the pinch gesture (un-pinch?) the "anchor point" for the zooming operation seems to be fairly random. By that I mean that sometimes the zoomed-in portion of the diagram seems to be the part of the diagram centered around the previous part of the diagram displayed. But sometimes it seems like the zoomed-in portion is such that the lower right corner remains the lower right corner, pushing the rest of the diagram off the left and top bounds. (As if the lower right corner was the "anchor point".)

I'm not very familiar with how these gestures are supposed to work. Maybe the un-pinch, depending on how it was done, is sometimes being interpreted as an un-pinch and a pan at the same time?

Anyway, for my app it is unfortunate when the un-pinch results in parts of the diagram being pushed off the left and top bounds. So I'd prefer that the un-pinch always perfroms the zoom in using the upper left corner as a kind of anchor point.

Does this make any sense to you? Any suggestions? Thanks.

Yes, I think we're seeing the same thing. Although what I'm experiencing may be influenced by the viewportChanged() method I've created to prevent the problems described on the other thread that affects zooming out.

What I'd like (I think) is some way of specifying that when zooming in is being done that the upper left point visible in the diagram as currently displayed should be the "anchor point", so it remains in the upper left corner of the view.

Anyway, it's very unfortunate for my app that what gets pushed out of the view when the user zooms in is mostly the upper left part of the diagram, or at least that's the way it is experienced.