# This program draws n boxes spaced evenly (distance 1) along a line, rotated by
# an angle of 'spindiff' radians relative to each other. (Dimension given by 'edge').
# Moving back and forth along the line is the "redbox", whose color is red.
# Each box has its color adjusted towards green (how fast is given by 'reddecay')
# This gives an effect of a red trail behind the redbox. The boxes are also rotated.

from visual import *

# Parameters governing motion, size, and colors.
spindiff = 0.08
reddecay = 0.05
nboxes = 180
edge = 1.

boxlist=[]
for boxnum in range(nboxes):
    theta = boxnum * spindiff              ## the angle of the box
    x = boxnum - nboxes/2. + 0.5           ## x-position of box center
    abox = box(height=edge*5, width=edge, length=edge, x=x, color=color.green,
               axis=(0,cos(theta),sin(theta)))
    abox.number = boxnum                   ## can add attributes to box
    boxlist = boxlist + [abox]             ## add the temporary abox to list

redbox = 0                                 ## start redbox at far left
redmove = 1                                ## start it moving to the right
t = 0

## repeat the dynamics forever
while 1:
#    rate(40)
    t = t + 1
    boxlist[redbox].color = color.red
    redbox = redbox + redmove
    if (redbox == nboxes - 1): redmove = -1  ## all the way to the right? move back left
    if (redbox == 0):  redmove = 1           ## if all the way to the left, move right
    for abox in boxlist:
        abox.axis = (0,cos((abox.number+t)*spindiff),sin((abox.number+t)*spindiff))
        ## The following line mixes current color and the green color to update the color
        ## Eventually, this turns a red box to a green box.
        abox.color = (1.-reddecay) * vector(abox.color) + reddecay * vector(color.green)