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)