Ability to read the current graph center

Hey Andrei,

Been reading through the code but can't figure out a way to retrieve the current transform from graphics.

The use case is to preserve the graph center and zoom-level after the graph container has been resized.

I have a (dirty) work around to preserve the zoom-level, but reading the current center seems impossible. I believe if I had the current center I would then be able to use renderer.moveTo()

Start by tracing how the graphics transform is stored and how renderer.moveTo() consumes positions. Determine whether the current graph center and zoom level are exposed together, then verify the result by resizing the graph container and confirming both values can be restored.

Written by the indexing model from the issue text.