def setup():
    size(100, 100, P3D)

def draw():
    background(204)
    x = mouseX
    y = mouseY
    z = -100
    # Draw "X" at z = -100
    stroke(255)
    line(x - 10, y - 10, z, x + 10, y + 10, z)
    line(x + 10, y - 10, z, x - 10, y + 10, z)
    # Draw gray line at z = 0 and same
    # x value. Notice the parallax
    stroke(102)
    line(x, 0, 0, x, height, 0)
    # Draw black line at z = 0 to match
    # the x value element drawn at z = -100
    stroke(0)
    theX = screenX(x, y, z)
    line(theX, 0, 0, theX, height, 0)