canvas issues #1

'''
December 17, 2019

This is an example application that allows scrolling a canvas and dragging boxes on a canvas.
I can't figure out how to make use of it though--I can't find any events that I can bind to to get information
about any changes that occur.

The canvas visible area is 300 x 300 px, but the scrollable area is 600 x 600 px.

1. How can I update the canvas horizontal & vertical scroll labels when that occurs?

2. How can I tell which box was moved after it was moved, or get its actual x-y location on the full scrollable canvas range?
'''

import tkinter as tk
from tkinter import ttk
from functools import partial


root = tk.Tk()
root.title( "Scroll/Drag Canvas Example 1.0" )
window_width = 900
window_height = 700
root.minsize(window_width, window_height)
window_position_x = 20
window_position_y = 20
root.geometry('%dx%d+%d+%d' % (window_width, window_height, window_position_x, window_position_y))
root.resizable(True, True)
window_test_color = '#%02x%02x%02x' % (160, 160, 160)
root.config(bg=window_test_color)

label_test_color = '#%02x%02x%02x' % (255, 180, 180)

# @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
# Below is the scrolling functionality (working)

canvas_test_color = '#%02x%02x%02x' % (100, 160, 100)
canvas1 = tk.Canvas(master=root, width=300, height=300, scrollregion=(0,0,600,600), bg=canvas_test_color)
canvas1.place(x=30, y=30)

hbar1 = tk.Scrollbar(master=root,orient=tk.HORIZONTAL)
hbar1.place(x=30, y=360, width=200, height=30)

vbar1 = tk.Scrollbar(master=root,orient=tk.VERTICAL)
vbar1.place(x=360, y=30, width=30, height=200)

hbar1.config(command=canvas1.xview)
vbar1.config(command=canvas1.yview)
canvas1.config(xscrollcommand=hbar1.set, yscrollcommand=vbar1.set)

# @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

# Below is trying to get the canvas scroll values.
# Nothing I tried worked, at all.

def show_canvas_scroll_values(event):
    canvas = event.widget
    x = canvas.canvasx(event.x)
    y = canvas.canvasy(event.y)
    #print canvas.find_closest(x, y)
    canvas_hposition_label.config(text=x)
    canvas_vposition_label.config(text=y)

#canvas1.bind('<Configure>', show_canvas_scroll_values)


# @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
# This section is just four labels to read out the canvas scroll values
# and the last-dragged-box actual xy values, on the 600x600 canvas area.

xpos=430
ypos=50
vspacer425 = 30
someLabel = tk.Label(master=root, text="canvas vertical scroll:")
someLabel.place(x=xpos, y=ypos)
xpos=570
canvas_hposition_label = tk.Label(master=root, text="???", bg=label_test_color)
canvas_hposition_label.place(x=xpos, y=ypos)

xpos=430
ypos=ypos + vspacer425
someLabel = tk.Label(master=root, text="canvas horizontal scroll:")
someLabel.place(x=xpos, y=ypos)
xpos=570
canvas_vposition_label = tk.Label(master=root, text="???", bg=label_test_color)
canvas_vposition_label.place(x=xpos, y=ypos)

xpos=430
ypos=ypos + vspacer425 + vspacer425
someLabel = tk.Label(master=root, text="box xpos:")
someLabel.place(x=xpos, y=ypos)
xpos=530
box_xposition_label = tk.Label(master=root, text="???", bg=label_test_color)
box_xposition_label.place(x=xpos, y=ypos)

xpos=430
ypos=ypos + vspacer425
someLabel = tk.Label(master=root, text="box ypos:")
someLabel.place(x=xpos, y=ypos)
xpos=530
box_yposition_label = tk.Label(master=root, text="???", bg=label_test_color)
box_yposition_label.place(x=xpos, y=ypos)



# @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
# this just draws the grid on the canvas.
    # canvas1 scroll region is 600 x 600

def draw_test_lines_on_canvas():
    tcolor1 = '#%02x%02x%02x' % (0, 0, 0)
    vspacing = 30
    hspacing = 100
    loopcount = 0
    tValue = vspacing
    while loopcount < 20:
        canvas1.create_line(0, tValue, 600, tValue, fill=tcolor1)
        tValue += vspacing
        loopcount += 1
    loopcount = 0
    tValue = hspacing
    while loopcount < 7:
        canvas1.create_line(tValue, 0, tValue, 600, fill=tcolor1)
        tValue += hspacing
        loopcount += 1

draw_test_lines_on_canvas()

# @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
# Below is the code for putting the 3 boxes on the canvas, and dragging them.

def canvas1_remember(event):
    global canvas1_former_pos
    canvas1_former_pos = event.x, event.y

canvas1.bind('<Button>', canvas1_remember)

def ondrag(box, event):
    global canvas1_former_pos
    canvas1.tag_raise(box) # <------------------------------------------ ???????????? what is this tag that is raised ???
    canvas1.move(box, event.x-canvas1_former_pos[0], event.y-canvas1_former_pos[1])
    canvas1_remember(event)

def add_box(x_pos, y_pos, color):
    box = canvas1.create_rectangle(x_pos, y_pos, x_pos+dragBox_width, y_pos+dragBox_height, outline="black", fill=color)
    canvas1.tag_bind(box, '<B1-Motion>', partial(ondrag, box))

canvas1_former_pos = 0,0
dragBox_width = 80
dragBox_height = 20

add_box(80, 100, 'red')
add_box(80, 200, 'green')
add_box(200, 200, 'blue')


# @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@


root.mainloop()