Re: [igraph] how to plot graph on matplotlib figure?

[Tamas Nepusz]

Hi,

> I would like to add my graph to a matplotlib figure but don't know how. Could 
> somebody please email me a code snippet showing how to do this? Or, if this 
> is not possible, how can you add titles, etc to an igraph.plot object?

As for matplotlib, I don't know the answer off the top of my head, but I guess 
it can be done with matplotlib's Cairo backend. igraph's plot() function and 
the Plot() class supports a keyword argument named "target", which can accept 
an arbitrary Cairo surface to plot on. If you can get the Cairo surface 
matplotlib plots on somehow, you can construct a Plot instance in igraph using 
this surface, call the .add() method of the Plot instance to add your graph to 
the plot and there you go. Alternatively, you can construct a Plot instance on 
its own and pass its .surface attribute to matplotlib if matplotlib supports 
that.

Another option I can think of right now for plotting a title to an igraph.plot 
object is to implement a plottable Title class yourself. If you dig deeper into 
igraph's drawing internals (in the API documentation of the Plot class), you 
will find that you can add arbitrary objects to a Plot instance, and igraph 
will call the __plot__ method of these objects when the plot is drawn. So, if 
you do something like this:

class Label(object):
  def __init__(self, text):
    self.text = text

  def __plot__(self, context, bbox, palette):
    # Call some Cairo methods on the given Cairo context to draw self.text
    # into the bounding box given by `bbox`
    [...]

then the following might work:

plot = Plot(bbox=(600, 600))
plot.add(your_graph)
title_label = Label("here comes the title of the plot")
plot.add(title_label, bbox=BoundingBox(0, 0, 600, 20))
plot.save()

I've never tried it, but if you manage to come up with a solution, please let 
me know and I will add it to igraph 0.6.

-- 
Tamas