from __future__ import division
from visual import *
from visual.controls import *
scene.background = color.white
scene.height = scene.width = 700
scene.x = scene.y = 0
scene.range = 25

def toggle_visible(object):
        object.visible = not(object.visible)

def toggle_spin():
    if rot_angle == 0:
        rot_angle = pi/2000
    else:
        rot_angle = 0

print '''for a passenger on a Ferris wheel, show r, p, both
useful in the "it feels as if something should be constant here..."
discussion '''

rot_angle = pi/2000    
fw = frame()

wheel = ring(pos=(0,0,0), axis=(0,0,1), radius = 20, color=color.magenta,
             frame = fw, thickness = .25)
for theta in arange(0, 2*pi, pi/6):
    a = sphere(pos = 1.05*wheel.radius*vector(cos(theta), cos(pi/2 + theta), 0),
           radius = .5, color=color.green, frame = fw)
a.color = color.blue  ## make one sphere a different color so it can be followed
aparr = arrow(color = (.22,.33,.64), axis=(0,0,0), frame = fw, shaftwidth = 1,
              fixedwidth=1, visible = 0)
zhat = vector(0,0,1)
aphat = norm(cross(a.pos, -zhat)) ## dir of momentum of a
aparr.pos = a.pos
aparr.axis = 11*aphat
ra = arrow(pos=(0,0,0), axis = a.pos, color=color.cyan, frame = fw, shaftwidth = 1,
           fixedwidth = 1, visible = 0)

c = controls(x = 700, y=0, width = 250, height = 250, range = 100)
tR = toggle(pos = (-30,25), width = 10, height = 30, text0='r invisible',text1='r visible',
            action = lambda: toggle_visible(ra))
tP = toggle(pos = (30,25), width = 10, height = 30, text0 = 'p invisible', text1 = 'p visible',
            action = lambda: toggle_visible(aparr))
while True:
    rate(300)
    fw.rotate(angle=rot_angle, axis = (0,0,1))
    c.interact()  ## check for control events