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 
    # y value. Notice the parallax
    stroke(102)
    line(0, y, 0, width, y, 0)
    # Draw black line at z = 0 to match 
    # the y value element drawn at z = -100 
    stroke(0)
    theY = screenY(x, y, z)
    line(0, theY, 0, width, theY, 0)