[graph-tool] positions of vertices

Good day to you. I'm trying to create pop-up windows in graph-tool graph. Using your advises I add a function, which making callback from the graph and give coordinates of my mouse pointer. But graph-vertices coordinates are not simular with gdk-window coordinates. In example: I placed some vertices, but a vertex with (0,0) coordinates not in left-up angle of the window. How I can get coordinates of vertices in gdk style? My pointer's coordinates of (0,0) are in left-up side of the window.