Tkinter - Why Is There Such A Thing Like Bbox?

Now that I'm working more with tkinter Canvas I was wondering about the use of bbox. For me I'm using bbox to get the coords of an element but the Canvas already have a method to r

Solution 1:

The difference is that with bbox() you can get the bounding box of a group of items (using a tag or 'all') while coords() returns the coordinates of the first item with given tag. Here is an example

import tkinter as tk

root = tk.Tk()
canvas = tk.Canvas(root)
canvas.pack()

i1 = canvas.create_rectangle(10, 10, 30, 50, tags='rect')
i2 = canvas.create_rectangle(60, 80, 70, 120, fill='red', tags='rect')

canvas.update_idletasks()
print('bbox', canvas.bbox('rect'))
print('coords', canvas.coords('rect'))

which gives

bbox

(9, 9, 71, 121)

coords

[10.0, 10.0, 30.0, 50.0]

One of the typical use of bbox() is when you want to scroll a group of widgets using a canvas: The scrollregion of the canvas needs to be set to include all the canvas content so canvas.bbox('all') is quite useful. See for instance Adding a scrollbar to a group of widgets in Tkinter (in the onFrameConfigure() function).

Solution 2:

Understanding bbox

Lets take this bit of Code here:

import tkinter as tk

def do_bbx(event):
    item_id = event.widget.find_withtag('current')[0]
    crds = event.widget.coords(item_id)
    print(f'{item_id} was clicked')
    print(f'bbox returns, {bbx}')
    print(f'coords returns, {crds}')

root = tk.Tk()
c = tk.Canvas(root,width=250,height=250)
f = c.create_rectangle(10,20, 50, 50,
                       fill = "BLUE")
sec = c.create_rectangle(30,30, 80, 80,
                         fill = "GREEN")
bbx = c.bbox(f, sec)
c.tag_bind('all', "<Button-1>", do_bbx)

c.pack()

root.mainloop()

and run this which return into this:

If you click on the blue rectangle the following will be printed out:

1 was clicked
bbox returns, (9, 19, 81, 81)
coords returns, [10.0, 20.0, 50.0, 50.0]

While clicking on the green will print:

2 was clicked
bbox returns, (9, 19, 81, 81)
coords returns, [30.0, 30.0, 80.0, 80.0]

So bbox does just quiet else then compareing the values of the coordinates and returns us a list. Like:

import tkinter as tk

def rectangel_us(canvas, *items):
    coords = {"x1":[],"y1":[],"x2":[],"y2":[]}
    for i in items:
        coords['x1'].append(canvas.coords(i)[0])
        coords['y1'].append(canvas.coords(i)[1])
        coords['x2'].append(canvas.coords(i)[2])
        coords['y2'].append(canvas.coords(i)[3])
    x1 = min(coords['x1'])-1
    y1 = min(coords['y1'])-1
    x2 = max(coords['x2'])+1
    y2 = max(coords['y2'])+1
    return[x1,y1,x2,y2]

root = tk.Tk()
c = tk.Canvas(root,width=250,height=250)
f = c.create_rectangle(10,20, 50, 50,
                       fill = "BLUE")
sec = c.create_rectangle(30,30, 80, 80,
                         fill = "GREEN")

bbx = rectangel_us(c, f, sec)
print(bbx)


c.pack()

root.mainloop()

the printed out bbx will be:

[9.0, 19.0, 81.0, 81.0]

as we know from above.

This can be visible by this code here:

import tkinter as tk

def rectangel_us(canvas, *items):
    coords = {"x1":[],"y1":[],"x2":[],"y2":[]}
    for i in items:
        coords['x1'].append(canvas.coords(i)[0])
        coords['y1'].append(canvas.coords(i)[1])
        coords['x2'].append(canvas.coords(i)[2])
        coords['y2'].append(canvas.coords(i)[3])
    x1 = min(coords['x1'])-1
    y1 = min(coords['y1'])-1
    x2 = max(coords['x2'])+1
    y2 = max(coords['y2'])+1
    canvas.create_rectangle(x1,y1,x2,y2,
                            outline='red')

root = tk.Tk()
c = tk.Canvas(root,width=250,height=250)
f = c.create_rectangle(10,20, 50, 50,
                       fill = "BLUE")
sec = c.create_rectangle(30,30, 80, 80,
                         fill = "GREEN")

bbx = rectangel_us(c, f, sec)


c.pack()

root.mainloop()

Which result in this: