Can I paint on the tkinter canvas twice simultaneously?-CodePudding

I want the cursor's x and y coordinates to be tracked by two sliding lines when the cursor is over a canvas. One on the top of the canvas constrained to x, and one at the left of the canvas constrained to y.

I have actually achieved this, almost:

import tkinter as tk

def callback(event):
    draw_y_marker(event.y)
    draw_x_marker(event.x)

def draw_x_marker(x):
    paint.coords(line, x, 0, x, 20)

def draw_y_marker(y):
    paint.coords(line, 0, y, 20, y)

root = Tk()
paint = Canvas(root)
paint.bind('<Motion>', callback)
paint.pack()

line = paint.create_line(x, 0, x, height)
root.mainloop()

If I comment out the draw_y_marker call in callback I get a the line constrained to x sliding along the top of the screen, marking cursor position. If I comment out draw_x_marker I get the line constrained to y sliding along the side of the screen.

But not both which is what I want! If I uncomment both, only the draw_x_marker method works. How can I paint two things on the canvas simultaneously?

CodePudding user response：

You have only created one line item in the canvas, so how can you show two sliding lines?

You need to create the two sliding lines for x and y and update them in callback():

import tkinter as tk

def callback(event):
    draw_y_marker(event.y)
    draw_x_marker(event.x)

def draw_x_marker(x):
    paint.coords(xline, x, 0, x, 20)

def draw_y_marker(y):
    paint.coords(yline, 0, y, 20, y)

root = tk.Tk()
paint = tk.Canvas(root)
paint.bind('<Motion>', callback)
paint.pack()

# create the two sliding lines initially
xline = paint.create_line(0, 0, 0, 0)
yline = paint.create_line(0, 0, 0, 0)

root.mainloop()