Snap image into place on canvas

[bpatt22]

How would you modify this gui code to designate only certain spots on your canvas to drop your image? Like when your playing solitaire and the game only allows you to drop your card in a certain spot.

http://www.daniweb.com/forums/post1111987.html#post1111987

[bpatt22]

Not a mod of code linked above, but it does what I was asking for:

import Tkinter as tk

class SnappingCanvas(tk.Canvas):
    ''' A canvas that bites! ;-)'''
    def __init__(self, master, **kw):
        self.click = None
        tk.Canvas.__init__(self, master, **kw)
        
        #for x in range (50,300,50): 
        #    self.create_line(x,0, x,500, tags='grid')
        #    self.create_line(0,x, 500,x, tags='grid')
            
        self.create_rectangle(0,0, 50,50, fill="green",
                              activefill='red', tag="R")
        self.tag_bind("R", "<Button-1>", self.onClick1)
        self.tag_bind("R", "<B1-Motion>", self.onMotion1)
        self.tag_bind("R", "<ButtonRelease-1>",self.onRelease1)

    def onClick1(self, event):
        self.click = event.x, event.y
        self.delete('cpoint')
        
    def onMotion1(self, event):
        x, y = self.click
        dx = event.x - x
        dy = event.y - y
        self.move('current' ,dx ,dy)
        self.click = event.x, event.y

    def onRelease1(self, event):
        #sx, sy, ex, ey = self.coords("R")
        #mx, my = (sx+ex)/2.0 , (sy+ey)/2.0
        mx, my = 100, 100 # this tells image where to snap into place
        x, y = mx-(mx%50), my-(my%50)
        self.coords("R", x,y, x+50,y+50)
        #self.coords("R", x,y, x+50,y+50)
        #self.create_oval(mx-2, my-2, mx+2, my+2, fill='magenta',
                         #tags='cpoint')


root = tk.Tk()
snapit = SnappingCanvas(root, width=300, height=300, bg="white")
snapit.pack()
root.mainloop()