from __future__ import division
from visual import *
# Bruce Sherwood, NCSU, February 2007
# Displays electron sea continually shifting due to nonzero electric field
scene.background = color.white
scene.foreground = color.black
scene.width = 900
scene.height = 450
hw = 4
hh = 1
scene.range = 2.3
d = hw/20
bar = d/2

def plus(x,y):
    box(pos=(x,y,0), size=(bar/4,bar,0), color=color.red)
    box(pos=(x,y,0), size=(bar,bar/4,0), color=color.red)

def minus(x,y, f):
    box(frame=f, pos=(x-bar/4,y+bar/2,0), size=(bar,bar/4,0), color=color.blue)

block = curve(pos=[(-hw,-hh,0),(-hw,hh,0),(hw,hh,0),(hw,-hh,0),(-hw,-hh,0)],
              color=color.black)
for x in arange(-hw+d/2,hw,d):
    for y in arange(-hh+d/2,hh,d):
        plus(x,y)

mobile = frame(pos=(0,0,0))
for x in arange(-hw+d/2,hw,d):
    for y in arange(-hh+d/2,hh,d):
        minus(x,y,mobile)

arrow(pos=(-1,0,0), axis=(2,0,0), color=color.orange)
label(pos=(0,0,0), text="Electric Field", opacity=0, box=0)
dx = 0.01
while 1:
    rate(50)
    mobile.pos.x -= 0.01
    if mobile.pos.x < -d:
        mobile.pos.x = 0