[graph-tool] slow plot generation with mplfig

I am using graph-tool to generate an animation. For this I need to use matplotlib because I should add some extra information to the plot. (see the attachment). so I first generate a series of plots and then use ffmpeg to generate my animation. The problem is when I use mplfig and savefig it takes alot of time to generate my png files. When I simply use output argument in graph_draw (that means no extra information, only nodes and edges) it is fast. Is there any solution for this? you can find the relevant parts of my code in the attachment. best, -- Mohsen