new functionality: set focus on creation

[pchtsp]

I work with networkx and I use the layout produced by it. The problem is that when the graph is produced in my notebook, the image is not centered and I cannot control where I want the zoom/view to start. I figure out that it tries to show the origin of coordinates (0, 0) and so now I modify the positions coming from networkx so that they're positioned around the (0, 0) coordinate.

Instead of this hack, maybe it could be useful to pass an argument to the gv.d3 function with the coordinates to display by default on the creation of the graph?

I guess this is only useful when someone is setting the coordinates manually as I'm doing.

Example:

G = my_instance.create_scenario_tree()
pos = nx.drawing.nx_pydot.graphviz_layout(G, prog="dot")

def prepare_graph(g):
  g = g.copy()
  x_coord = {v[1] for v in pos.values()}
  y_coord = {v[0] for v in pos.values()}
  max_y, min_y = max(y_coord), min(y_coord)
  max_x, min_x = max(x_coord), min(x_coord)

  for node_id in g.nodes:
    node = g.nodes[node_id]
    node['x'] = (-pos[node_id][1] + (max_x-min_x)/2)*4
    node['y'] = (pos[node_id][0] - (max_y-min_y)/2)/3
  return g


gv.d3(prepare_graph(G), zoom_factor=0.2, node_label_size_factor=3, show_node_label_border=True, graph_height=500, layout_algorithm_active=False)