Processing

import processing.serial.*;

Serial puerto;
int cont = 0;
int lectura = 0;

void setup() {
  println(Serial.list());
  puerto = new Serial(this, Serial.list()[0], 9600);
  size(400,400);
  frameRate(60);
}

void draw() {
  background(lectura);

  if (puerto.available() > 0) {
    lectura = puerto.read();
    println(lectura);
  }

  fill(255);
  strokeWeight(5);
  stroke(33);
  smooth();
  line(100,100,100,300);
  line(100,300,50,300);
  line(50,300,50,250);
  line(50,250,100,250);

  strokeWeight(1);
  ellipse(mouseX,mouseY,5,5);

  fill(204, 102, 0, 50);
  rect(cont, 20, 55, 55);
  rect(40, cont, 55-cont/2, 55);
  cont++;
  if(cont==400) cont = -55;
}

Arduino

int cont = 0;

void setup(){
  Serial.begin(9600);  
}

void loop(){

  Serial.print(cont,BYTE);
  cont++;
  if (cont>255) cont = 0;
  delay(200);

}