PImage elevator;
int yPos=0, elevatorPos;
boolean start;
int inverter, down;

void setup() {
  size(200, 400);
  background(255);
  elevator = loadImage("elevator.jpg");
}

void draw() {
  background(255);

  strokeWeight(4);
  line(width/2, 0, width/2, height);


  start = (mousePressed && (mouseButton == LEFT));

  //Condition

  if (start) {

    yPos = yPos +1;

    if (inverter % 2 != 0) {
      down = down +2;
    }
  }

  //Modulo

  inverter = yPos/(height-elevator.height);

  //Lift Movement


  elevatorPos= (height-elevator.height) - yPos + down;


  println(elevatorPos);

  //LiftImage


  image(elevator, width/2-elevator.width/2, elevatorPos);
}