How to connect two state circles with an arrow in tkinter?

I am currently writing a fsm editor with tkinter. But, I stuck on connecting two states. I have two questions:

1) How can make the transition arrow growable according to mouse movement?

2) How can I stick the starting point of the arrow on a state and the end point of the arrow on another state?

PS. Do you think the documentation of tkinter is good enough?

Solution

Here's an example that shows the concept. In a nutshell, use tags to associate lines with boxes, and simply adjust the coordinates appropriately when the user moves the mouse.

Run the example, then click and drag from within the beige box.

Of course, for production code you need to make a more general solution, but hopefully this shows you how easy it is to create a box with arrows that adjust as you move the box around.

from Tkinter import *

class CanvasDemo(Frame):
    def __init__(self, width=200, height=200):
        Frame.__init__(self, root)
        self.canvas = Canvas(self)
        self.canvas.pack(fill="both", expand="1")
        self.canvas.create_rectangle(50, 25, 150, 75, fill="bisque", tags="r1")
        self.canvas.create_line(0,0, 50, 25, arrow="last", tags="to_r1")
        self.canvas.bind("<B1-Motion>", self.move_box)
        self.canvas.bind("<ButtonPress-1>", self.start_move)

    def move_box(self, event):
        deltax = event.x - self.x
        deltay = event.y - self.y
        self.canvas.move("r1", deltax, deltay)
        coords = self.canvas.coords("to_r1")
        coords[2] += deltax
        coords[3] += deltay
        self.canvas.coords("to_r1", *coords)
        self.x = event.x
        self.y = event.y

    def start_move(self, event):
        self.x = event.x
        self.y = event.y

root = Tk()
canvas = CanvasDemo(root)
canvas.pack()
mainloop()