accelerate = ->
    for a in [0...size-4] by 4
        x1 = particles[a+0]
        y1 = particles[a+1]
        for b in [a+4...size] by 4
            x2 = particles[b+0]
            y2 = particles[b+1]
            xd = x2-x1
            yd = y2-y1
            l2 = xd*xd + yd*yd
            if l2 > nearest
                l = Math.sqrt(l2)
                xn = xd/l
                yn = yd/l
                acc = factor/l2
                xa = xn*acc
                ya = yn*acc
                particles[a+2] += xa
                particles[a+3] += ya
                particles[b+2] -= xa
                particles[b+3] -= ya
    return

move = ->
    for i in [0...size] by 4
        x2 = particles[i+2]
        y2 = particles[i+3]
        xv = (x2 - particles[i+0])
        yv = (y2 - particles[i+1])
        l = Math.sqrt(xv*xv + yv*yv)
        if l > limit
            xv = (xv/l) * limit
            yv = (yv/l) * limit

        x = x2 + xv
        y = y2 + yv

        particles[i+0] = x - xv
        particles[i+1] = y - yv
        particles[i+2] = x
        particles[i+3] = y
    return