from Tkinter import *

# allows moving dots with multiple selection. 

SELECTED_COLOR = "red"
UNSELECTED_COLOR = "blue"

class Test(Frame):
    ###################################################################
    ###### Event callbacks for THE CANVAS (not the stuff drawn on it)
    ###################################################################
    def mouseDown(self, event):
	# see if we're inside a dot. If we are, it
	# gets tagged as "current" for free by tk.

	if not event.widget.find_withtag("current"):
	    # we clicked outside of all dots on the canvas. unselect all.
	    
	    # re-color everything back to an unselected color
	    self.draw.itemconfig("selected", {"fill" : UNSELECTED_COLOR})
	    # unselect everything
	    self.draw.dtag("selected")
	else:
	    # mark as "selected" the thing the cursor is under
	    self.draw.addtag("selected", "withtag", "current")
	    # color it as selected
	    self.draw.itemconfig("selected", {"fill": SELECTED_COLOR})

	self.lastx = event.x
	self.lasty = event.y
		
	
    def mouseMove(self, event):
	self.draw.move("selected", event.x - self.lastx, event.y - self.lasty)
	self.lastx = event.x
	self.lasty = event.y

    def makeNewDot(self):
	# create a dot, and mark it as current
	fred = self.draw.create_oval(0, 0, 20, 20, 
				     {"fill" : SELECTED_COLOR, "tag" : "current"})
	# and make it selected
	self.draw.addtag("selected", "withtag", "current")
	
    def createWidgets(self):
	self.QUIT = Button(self, {'text': 'QUIT', 
				  'fg': 'red', 
				  'command': self.quit})

	################
	# make the canvas and bind some behavior to it
	################
	self.draw = Canvas(self, {"width" : "5i", "height" : "5i"})
	Widget.bind(self.draw, "<1>", self.mouseDown)
	Widget.bind(self.draw, "<B1-Motion>", self.mouseMove)


	# and other things.....
	self.button = Button(self, {"text" : "make a new dot",
				    "command" : self.makeNewDot,
				    "fg" : "blue"})

	self.label = Message(self,
			     {"width" : "5i", 
			      "text" : SELECTED_COLOR + " dots are selected and can be dragged.\n" +
   			               UNSELECTED_COLOR + " are not selected.\n" +
				             "Click in a dot to select it.\n" +
				             "Click on empty space to deselect all dots." })

	self.QUIT.pack({'side': 'bottom', 'fill': 'both'})	
	self.label.pack({"side" : "bottom", "fill" : "x", "expand" : 1})
	self.button.pack({"side" : "bottom", "fill" : "x"})
	self.draw.pack({'side': 'left'})
	

    def __init__(self, master=None):
	Frame.__init__(self, master)
	Pack.config(self)
	self.createWidgets()

test = Test()
test.mainloop()