Tkinter - creating a second canvas displays the contents of another

Question

I am looking for a way to make one canvas display the contents of another WITHOUT duplicating objects that are drawn in it. The second canvas should be just a display that accepts as input what is drawn on the first.

I know that the .postscript method writes the contents to a file or variable, but I do not know how (if possible) to make another canvas display it as an image.

Edit: I forgot to mention, my operating system is windows. It would be great if someone could tell me a cross-platform solution.

Edit2: the reason I don’t want to do this, duplicating objects, is that they move and at some interval some of them are destroyed, and new ones are created. In addition, a real-time system and duplication of objects with their behavior can slow down the work.

Answer 1

There is no built-in way to do this. Canvas does not support any peering or duplication. However, saving copies of all objects in the second canvas is quite easy and fast if you do not have built-in widgets.

An easy way to do this is to subclass the canvas widget and then create new implementations of draw_line, draw_oval, coords, etc. for drawing on a peer canvas. The following example shows how to match three canvases with 1000 objects that move down at different speeds:

import Tkinter as tk import random class SampleApp(tk.Tk): def __init__(self, *args, **kwargs): tk.Tk.__init__(self, *args, **kwargs) self.canvas1 = PeeredCanvas(self, width=300, height=300, border=1, relief="sunken") self.canvas2 = PeeredCanvas(self, width=300, height=300, border=1, relief="sunken") self.canvas3 = PeeredCanvas(self, width=300, height=300, border=1, relief="sunken") self.canvas1.add_peer(self.canvas2) self.canvas1.add_peer(self.canvas3) toolbar = tk.Frame(self) clear_button = tk.Button(self, text="Refresh", command=self.refresh) clear_button.pack(in_=toolbar, side="left") toolbar.pack(side="top", fill="x") self.canvas1.pack(side="left", fill="both", expand=True) self.canvas2.pack(side="left", fill="both", expand=True) self.canvas3.pack(side="left", fill="both", expand=True) self.animate(10) def animate(self, delay): '''Move all items down at a random rate''' for item in self.canvas1.find_all(): delta_x = 0 delta_y = random.randrange(1, 4) self.canvas1.move(item, delta_x, delta_y) self.after(delay, self.animate, delay) def refresh(self, count=100): '''Redraw 'count' random circles''' self.canvas1.delete("all") width=self.canvas1.winfo_width() height=self.canvas1.winfo_height() for i in range(count): if i%2 == 0: tags = ("even",) else: tags = ("odd",) x = random.randrange(10, width-10) y = random.randrange(10, height-10) radius = random.randrange(10,100, 10)/2 self.canvas1.create_oval([x,y, x+radius, y+radius], tags=tags) self.canvas1.itemconfigure("even", fill="red", outline="white") self.canvas1.itemconfigure("odd", fill="white", outline="red") class PeeredCanvas(tk.Canvas): '''A class that duplicates all objects on one or more peer canvases''' def __init__(self, *args, **kwargs): self.peers = [] tk.Canvas.__init__(self, *args, **kwargs) def add_peer(self, peer): if self.peers is None: self.peers = [] self.peers.append(peer) def move(self, *args, **kwargs): tk.Canvas.move(self, *args, **kwargs) for peer in self.peers: peer.move(*args, **kwargs) def itemconfigure(self, *args, **kwargs): tk.Canvas.itemconfigure(self, *args, **kwargs) for peer in self.peers: peer.itemconfigure(*args, **kwargs) def delete(self, *args, **kwargs): tk.Canvas.delete(self, *args) for peer in self.peers: peer.delete(*args) def create_oval(self, *args, **kwargs): tk.Canvas.create_oval(self, *args, **kwargs) for peer in self.peers: peer.create_oval(*args, **kwargs) app = SampleApp() app.mainloop()