# -*- coding: utf-8 -*-
# ball_collide.py
# MIT OCW 6.189 Homework 3
# Exercise 3.2 – Collision Detection of Balls
# Mechanical MOOC
# Judy Young
# July 23, 2013
# To figure out if two balls are colliding, we need to compute the distance 
# between their centers, then see if this distance is less than or equal to 
# the sum of their radii. If so, they are colliding.
 
import math
 
def ball_collide(ball_1, ball_2):
 
    sumRadii = float(ball_1[3] + ball_2[3])
    xDiffSquared = (float(ball_1[0]) - float(ball_2[0]))**2
    yDiffSquared = (float(ball_1[1]) - float(ball_2[1]))**2
    zDiffSquared = (float(ball_1[2]) - float(ball_2[2]))**2
    centreDistance = math.sqrt( xDiffSquared + yDiffSquared + zDiffSquared )
 
    print "\nball_1", ball_1
    print "ball_2", ball_2
    print "sumRadii = ", sumRadii
    print "xDiffSquared = ", xDiffSquared
    print "yDiffSquared = ", yDiffSquared
    print "zDiffSquared = ", zDiffSquared
    print "centreDistance = ", centreDistance
 
    if centreDistance > sumRadii:
        return "All Clear\n"
    else:
        return "CRASH!\n"
 
print "Balls small, far apart", ball_collide((0,0,0,1), (7,7,7,1))
print "Both balls the same size, in the same place", ball_collide((0,0,0,1), (0,0,0,1))
print "Both balls in the same place, different sizes", ball_collide((0,0,0,1), (0,0,0,7))
print "Balls just touching", ball_collide((0,0,0,1), (0,2,0,1))
print "Balls small, far apart, each side of 0,0,0", ball_collide((-5,-5,-5,1), (0,2,0,1))

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