cpython/Demo/tkinter/matt/canvas-moving-w-mouse.py

from tkinter import *

# this file demonstrates the movement of a single canvas item under mouse control

class Test(Frame):
    ###################################################################
    ###### Event callbacks for THE CANVAS (not the stuff drawn on it)
    ###################################################################
    def mouseDown(self, event):
        # remember where the mouse went down
        self.lastx = event.x
        self.lasty = event.y

    def mouseMove(self, event):
        # whatever the mouse is over gets tagged as CURRENT for free by tk.
        self.draw.move(CURRENT, event.x - self.lastx, event.y - self.lasty)
        self.lastx = event.x
        self.lasty = event.y

    ###################################################################
    ###### Event callbacks for canvas ITEMS (stuff drawn on the canvas)
    ###################################################################
    def mouseEnter(self, event):
        # the CURRENT tag is applied to the object the cursor is over.
        # this happens automatically.
        self.draw.itemconfig(CURRENT, fill="red")

    def mouseLeave(self, event):
        # the CURRENT tag is applied to the object the cursor is over.
        # this happens automatically.
        self.draw.itemconfig(CURRENT, fill="blue")

    def createWidgets(self):
        self.QUIT = Button(self, text='QUIT', foreground='red',
                           command=self.quit)
        self.QUIT.pack(side=LEFT, fill=BOTH)
        self.draw = Canvas(self, width="5i", height="5i")
        self.draw.pack(side=LEFT)

        fred = self.draw.create_oval(0, 0, 20, 20,
                                     fill="green", tags="selected")

        self.draw.tag_bind(fred, "<Any-Enter>", self.mouseEnter)
        self.draw.tag_bind(fred, "<Any-Leave>", self.mouseLeave)

        Widget.bind(self.draw, "<1>", self.mouseDown)
        Widget.bind(self.draw, "<B1-Motion>", self.mouseMove)

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

test = Test()
test.mainloop()