# Tk_Gravity.py

# Tk_Gravity.py

from Tkinter import *
import random
import time

root = Tk()
root.resizable(0,0)

ww = 500
hh = 400

canvas = Canvas(root, width=ww, height=hh)

def ready():
    canvas.create_text(ww/2, hh/2-60, text='Click Here', font=("Helvetica", "32"),
        anchor=CENTER, fill='red')
ready()
canvas.pack()

root.wm_title("Gravity")

n = 120
x = [None]*n
y = [None]*n
vy = [None]*n
vx = [None]*n
id = [None]*n
g = 0.05
cor = 0.7
fr = 0.95
r = 16
xx = 300
yy = 100

def init():
    canvas.delete(ALL)
    for i in range(n):
        # canvas.delete(id[i])
        x[i] = xx
        y[i] = yy
        vx[i] = 16*(random.random()-.5)
        vy[i] = 2*(random.random()-.5)
        id[i] = canvas.create_oval(300-8, 25, 300+8, 25+16, fill="red")

def updateY(i):
    if ((y[i]+r) < hh):
        vy[i] += g
    else:
        vy[i] = -vy[i]*cor
        vx[i] *= fr
    y[i] += vy[i]
    if ((y[i]+r) > hh):
        y[i] = hh-r
#
def updateX(i):
    if x[i]+r >= ww or x[i]-r <= 0:
        vx[i] = -vx[i]*cor
    x[i] += vx[i]
    if x[i]+r > ww:
        x[i] = ww-r
    elif x[i]-r < 0:
        x[i] = r
#
def on_canvas_click(ev):
    global action
    init()
    action=1
#
canvas.bind('<Button-1>', on_canvas_click)

start=time.time()
go=1
action=0
while go:
    if action:
        inMotion=''
        if time.time() > start + 0.015:
            start=time.time()
            for i in range(n):
                updateX(i)
                updateY(i)
                if abs(vx[i])+abs(vy[i]) > 0.2:
                    canvas.move(id[i], vx[i], vy[i])
                    inMotion=True
            if not inMotion: ready()

    root.update()