from math import pi

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 = 1000
    # the animation will cycle through 4 different "scenes"
    iscene = (frameCount/sceneframes)%6
    # frame number within this scene
    isceneframe = frameCount%sceneframes
    # cook up a "time" that loops from tmin to tmax within each scene
    tmin = -1.0; tmax = +23.0; dt = (tmax-tmin)/sceneframes
    t = tmin + isceneframe*dt
    # speed of wave propagation
    vwave = 2.0
    # wavelength etc.
    N = iscene + 1
    Lambda = 20.0/N
    k = 2*pi/Lambda
    omega = vwave*k
    # 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
        psi = sin(k*x) * sin(omega*t)
        if t<0 or t>22: psi = 0.0
        # 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