////////////////////////////add
import processing.serial.*;
Serial myPort;
int x;
////////////////////////////added

float max_distance;

void setup() {
  size(640, 360);
  noStroke();
  max_distance = dist(0, 0, width, height);

  myPort = new Serial(this, "/dev/cu.usbmodem14401", 9600); //port////add

}

void draw() {
  background(0);

  for(int i = 0; i <= width; i += 20) {
    for(int j = 0; j <= height; j += 20) {
      float size = dist(x, mouseY, i, j);//////// changed mouseX to X
      size = size/max_distance * 66;
      ellipse(i, j, size, size);
    }
  }
}

////////////////////////////add
void serialEvent(Serial p){
  x = p.read(); // read value from serial
  println(x);
}
////////////////////////////added