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canvas python tkinter overlap

How can I find overlapping objects on a tkinter canvas?

发布于 2020-04-10 16:08:26

is there any easy way to find the objects ids that are overlapped? Here's an example of the code:

import tkinter as tk
import random as rand


class GUI:
    def __init__(self, master, width, height):
        self.master = master
        self.w = width
        self.h = height
        self.canvas = tk.Canvas(master, width=width, height=height)
        self.canvas.pack()
        self.create_objects()

    def create_objects(self):
        r = 5
        for i in range(100):
            x = rand.uniform(0,1)*width
            y = rand.uniform(0,1)*height
            self.canvas.create_oval(x-r,y-r,x+r,y+r, fill="red")

    def find_overlaps(self):
        pass


width = 800
height = 600

root = tk.Tk()
app = GUI(root, width, height)
root.mainloop()

I would like for the find_overlaps function to give me the pairs of the object ids that are overlapped (or tripplets if such case happen). Is there any easy/efficient way to do it?

Questioner
Daniel Casasampera
Viewed
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mathfux 2020-02-02 05:42

Here are steps that is possible for you to do here:

  1. Get the tuples of ids of objects you have created on canvas. You can do it using canvas.find_all() method.
  2. Get coordinates of these objects using canvas.coords(id).

I have checked out standard find_overlapping method of canvas. It helps to determine which object are overlapped with specific rectangle only and I guess you need to solve problem you mentioned using some mathematics with a help of this method. Although, I have found a nice alternative, not based on find_overlapping:

def find_overlaps(self):
    r = 5
    X = []
    tags = self.canvas.find_all() #finds tags of all the object created
    for tag in tags:
        x0, y0, x1, y1 = self.canvas.coords(tag) # corresponding coordinates
        center = [(x0+x1)/2, (y0+y1)/2] #centers of objects
        X.append(center)

    tree = cKDTree(X)
    print(tree.query_pairs(2*r))

Output

This is a set of couples of tags:

{(2, 63), (10, 93), (70, 82), (8, 45)}

Note

from scipy.spatial import cKDTree is required

Daniel Casasampera 2020-02-02 06:12:26

Thanks a lot!, this is what i needed. Which of the two methods do you think is best?

mathfux 2020-02-02 19:27:17

find_overlapping doesn't find result straightforwardly, you'll need to do the checkings for each rectangle on yourself. Another difference is that cKDTrees is precise only if objects are circles.

Daniel Casasampera 2020-02-02 23:17:49

Thank you very much, that was really helpfull, since my objects are circles i will use the cKDTrees approach then.

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