def setup():
    size(1000, 500)

def draw():
    # clear canvas to white background color
    background(255)
    # transform to scene coordinates, as pixel coordinates are annoying
    translate(0, 0.5+height/2.0)
    scale(width/10.0, -height/5.0)
    strokeWeight(0.02)
    # the number of frames per "scene"
    sceneframes = 800
    # frame number within this scene
    isceneframe = frameCount%sceneframes
    # cook up a "time" that loops from tmin to tmax within each scene
    tmin = +2.0; tmax = +42.0; dt = (tmax-tmin)/sceneframes
    t = tmin + isceneframe*dt
    # speed of wave propagation
    vwave = 1.0
    # width of gaussian wave packet
    sigma = 0.5
    # positions of the two wave packets' centers
    x1 = vwave*t
    x2 = vwave*(20-t)
    x3 = vwave*(t-20)
    x4 = vwave*(40-t)
    x5 = vwave*(t-40)
    # loop over x axis positions to draw the wave function psi(x)
    xmin = 0.0; xmax = 10.0; dx = (xmax-xmin)/width
    xlast = 0.0; psilast = 0.0
    for ix in range(width):
        x = xmin + ix*dx
        # calculate the two wave functions psi1(x) and psi2(x)
        psi1 = +1.0 * exp(-0.5*((x-x1)/sigma)**2)
        psi2 = +1.0 * exp(-0.5*((x-x2)/sigma)**2)
        psi3 = -1.0 * exp(-0.5*((x-x3)/sigma)**2)
        psi4 = -1.0 * exp(-0.5*((x-x4)/sigma)**2)
        psi5 = +1.0 * exp(-0.5*((x-x5)/sigma)**2)
        psi = psi1 + psi2 + psi3 + psi4 + psi5
        # draw line segment from previous point to this point
        line(xlast, psilast, x, psi)
        # this point becomes "previous" point for next iteration
        xlast, psilast = x, psi