from __future__ import print_function, division
from visual import *

## impact parameter
##b = 0
b = 15e-15  
##b = 80e-15

projectileproperties = (2,4) # alpha particle charge/e, mass/mp
##projectileproperties = (-1,(9e-31/1.7e-27))    ## electron

targetproperties = (8,16) # oxygen nucleus charge/3, mass/mp
##targetproperties = (2,4) # alpha particle
##targetproperties = (1,(9e-31/1.7e-27))    ## positron

rpscale = 2 ## make radii bigger for visual impact
parroVisible = 1

scene.width = 1000
scene.height = 750
scene.x = scene.y = 0
scene.background = color.white
scene.fov = 0.01
scene.range = 200e-15
xstart = scene.range.x*0.95

kcoul = 9e9
qe = 1.6e-19
mproton = 1.7e-27
rproton = 1.3e-15*rpscale
alpha = sphere(pos=(-xstart,b,0), color=color.red)
target = sphere(pos=(0,0,0), color=color.blue)
alpha.mass = projectileproperties[1]*mproton
alpha.radius = (alpha.mass/mproton)**(1./3.)*rproton
alpha.q = projectileproperties[0]*qe
ke = 1e6*qe
alpha.p = vector(sqrt(2.*alpha.mass*ke),0,0)
alpha.trail = curve(color=alpha.color)
target.mass = targetproperties[1]*mproton
target.radius = (target.mass/mproton)**(1./3.)*rproton
target.q = targetproperties[0]*qe
target.p = vector(0,0,0)
target.trail = curve(color=target.color)
dt = (5.*xstart/(mag(alpha.p)/alpha.mass)/1e5)*1
ptot = alpha.p+target.p
vcm = ptot/(alpha.mass+target.mass)

pscale = 40e-15/4e-20
paarro = arrow(pos=alpha.pos, axis=alpha.p*pscale, color=color.cyan,
               shaftwidth = 0.5*alpha.radius, fixedwidth=1, visible=parroVisible)
ptarro = arrow(pos=target.pos, axis=target.p*pscale, color=color.magenta,
               shaftwidth = 0.5*alpha.radius, fixedwidth=1, visible=parroVisible)

##alpha.p = alpha.p-alpha.mass*vcm
##target.p = target.p-target.mass*vcm

##scene.autoscale = 0
scene.mouse.getclick()  ## click to start particle moving
while 1:
    r12 = alpha.pos-target.pos
    F = (kcoul*alpha.q*target.q/mag(r12)**2)*norm(r12)
    alpha.p = alpha.p + F*dt
    target.p = target.p - F*dt
    alpha.pos = alpha.pos + (alpha.p/alpha.mass)*dt
    target.pos = target.pos + (target.p/target.mass)*dt
    paarro.pos = alpha.pos
    paarro.axis = alpha.p*pscale
    ptarro.pos = target.pos
    ptarro.axis = target.p*pscale
    alpha.trail.append(pos=alpha.pos)
    target.trail.append(pos=target.pos)
    if scene.mouse.clicked:
        scene.mouse.getclick()  ## take original click
        scene.mouse.getclick()  ## pause and wait for new click