# Using some basic Newtonian physics (G = gm1m2/r^2, F = MA) to create a still 
# drawing. There are two "gravs" -- particles with gravity pulls that affect 
# the flow of the other particles.
# grav-42-50.pdf displays the weird effect that occurs when the ratio of the 
# masses is 42:50.

import sys
sys.path.append('/Users/apollotiger/lib')
from euclid import *
from math import tan

class Particle:
    def __init__(self,locus=Vector2(0,750),mass=5,radius=2,color=(255,255,255),mother=False):
        self.radius = radius 
        self.mass = mass
        self.locus = locus
        self.velox = Vector2(0,0)
    def distance(self,locus):
        return ((self.locus.x - locus.x) ** 2 + (self.locus.y - locus.y) ** 2) ** 0.5

def movement():
    global lastpart,gravs
    newpart = lastpart
    for grav in gravs:
        distance = newpart.distance(grav.locus)
        force = 0.6 * newpart.mass * grav.mass / distance ** 2
        acceleration = force / newpart.mass
        newpart.velox += acceleration * (newpart.locus - grav.locus) / distance
    if 0 > newpart.locus.x - newpart.velox.x: newpart.velox.x *= -1
    if 0 > newpart.locus.y - newpart.velox.y: newpart.velox.y *= -1
    if WIDTH < newpart.locus.x - newpart.velox.x: newpart.velox.x *= -1
    if HEIGHT < newpart.locus.y - newpart.velox.y: newpart.velox.y *= -1
    newpart.locus -= newpart.velox
    lastpart = newpart
    fill(0)

size(180,180)
fill(0,0,0)
rect(0,0,HEIGHT,WIDTH)
lastpart = Particle(Vector2(80,80 - (140 ** 2 - 70 ** 2) ** 0.5 / 2.0),10,3)
gravs = [Particle(Vector2(35,80),50,10),
         Particle(Vector2(130,80),42,10)]
# Stable orbit between the two bodies occurs when the ratio is 50:42
fill(1,1,1)
for grav in gravs:
    oval(grav.locus.x,grav.locus.y,grav.radius,grav.radius)
for a in range(2000):
    movement()
    fill(0.6,0.6,1,0.15)
    oval(lastpart.locus.x,lastpart.locus.y,lastpart.radius,lastpart.radius)