overlapping vertex patches and labels

[iosonofabio]

Since vertex patches and their labels are somewhat separate, some weird race condition about overlap might incur (see traveling salesman example, but with a edgecolor!='none'.

This one might be nontrivial and require a little thought about order of children in the network artist.

[iosonofabio]

Just a small addition: almost the only property of patches within a collection that cannot be set on a per-patch basis is zorder. That makes it a bit tricky because if two vertices are overlapping, the order of rendering should be bottom vertex->bottom label->top vertex->top label

[iosonofabio]

This is part of a larger issue with zorder between elements. The obvious current conflict is edges being plotted after nodes. That can look really crowded in many cases.

We could spllit the node rendering into 1. compute all coordinates, extents, etc., and 2. draw. That way we could insert edge drawing in the middle if the user requested the appropriate zorder.

[iosonofabio]

51aa6c3 introduced correct handling of zorder for vertices and edges. Labels are still broken.