Question

So i’ve this code who create moving balls :

from Tkinter import *
from random import randrange
from threading import Thread

Matrice = (600*400)*[0]

class Ball(Frame):

    def __init__(self, can, posx, posy, name):
        self.can = can

        self.largeur_can = int(self.can.cget("width"))
        self.hauteur_can = int(self.can.cget("height"))

        self.posx = posx
        self.posy = posy
        self.name = name 

        self.ball1 = self.can.create_oval(self.posy, self.posx, self.posy+10, self.posx+10, outline="red", fill=self.name, width=2)

        self.nx = randrange(-10,10,1)
        self.nx /= 2.0
        self.ny = randrange(-10,10,1)
        self.ny /= 2.0


        self.move()

    def move(self):
        global Matrice
        self.pos_ball = self.can.coords(self.ball1)
        self.posx_ball = self.pos_ball[0]
        self.posy_ball = self.pos_ball[1]

        if self.posx_ball < 0 or (self.posx_ball + 10) > self.largeur_can:
            self.nx = -self.nx         
        if self.posy_ball < 0 or (self.posy_ball + 10) > self.hauteur_can:
            self.ny = -self.ny

        self.can.move(self.ball1, self.nx, self.ny)

        Matrice[int(self.posy_ball)*600 + int(self.posx_ball)] += 100

        self.can.after(10, self.move)



root=Tk()
can=Canvas(root,width=600,height=400,bg="black")
for x in range(10):
    x=Ball(can,100,400, "blue")
    x=Ball(can,100,400, "green")
can.pack()
root.mainloop()

And i would create traces behind balls, i created a matrix Matrice where I recorded where each ball is passed and now i want to show it un the background but i don’t know how.
Nota : values in the matrix could decrease or be changed somewhere other than in move.
So anyone have an idea how i could do that ?

Answer 1

This is an inefficient way of doing it, but it’s the simplest. Every time you move a ball just draw a line from where it used to be to where it currently is.

self.can.move(self.ball1, self.nx, self.ny)

new_pos = self.can.coords(self.ball1)
self.can.create_line(self.posx_ball, self.posy_ball, new_pos[0], new_pos[1], fill='red')

self.can.after(10, self.move)

Note that this line will follow the top left of the sprite – you can adjust the coordinates if you want it to follow the middle of the sprite.