from __future__ import print_function
try:
    import Tkinter
except ImportError:
    import tkinter as Tkinter

#
# Create a GUI with a canvas where the user can draw
# lines using the mouse.
#
class CanvasDemo:

    # __init__() and run() together serve the same
    # purpose as the main() function in other examples.
    def __init__(self):
        self.x = 0
        self.y = 0
        self.app = Tkinter.Frame()
        self.app.grid(sticky="nsew")
        self.make_ui(self.app)

        top = self.app.winfo_toplevel()
        top.columnconfigure(0, weight=1)
        top.rowconfigure(0, weight=1)

    def run(self):
        self.app.mainloop()

    # "make_ui" is similar to the one in tkinter_canvas.py
    def make_ui(self, app):
        b = Tkinter.Button(app, text="Clear", command=self.clear)
        b.grid(row=1, column=0, sticky="ew")
        c = Tkinter.Canvas(app, width=400, height=400, bg="cyan")
        app.columnconfigure(0, weight=1)
        app.rowconfigure(0, weight=1)
        c.grid(row=0, column=0, sticky="nsew")

        # When button is pressed, execute self.on_select
        c.bind("<Button-1>", self.on_select)
        # When button is released, execute self.on_release
        c.bind("<ButtonRelease-1>", self.on_release)
        self.handler = None
        self.canvas = c

    # "clear" is called when the user presses the "Clear"
    # button.  We clear the canvas of all the lines we
    # created by deleting all items marked with tag "line".
    def clear(self):
        self.canvas.delete("line")

    # "on_select", "on_drag" and "on_release" are event
    # handlers that get called when the mouse button is
    # pressed down, dragged and released, respectively.
    # On press, we record the mouse position and bind to
    # mouse motion=drag.  On drag, we add a line from the
    # previous position to the current position, and record
    # the current position.  On release, we add a line from
    # the previous position and unbind from mouse motion.
    def on_select(self, event):
        self.x = event.x
        self.y = event.y
        self.handler = self.canvas.bind("<B1-Motion>", self.on_drag)

    def on_drag(self, event):
        self.canvas.create_line(self.x, self.y, event.x, event.y,
                    fill="black", tags="line")
        self.x = event.x
        self.y = event.y

    def on_release(self, event):
        self.canvas.create_line(self.x, self.y, event.x, event.y,
                    fill="black", tags="line")
        self.canvas.unbind("<B1-Motion>", self.handler)
        self.handler = None

if __name__ == "__main__":
    CanvasDemo().run()
    print("Finished")