graph.pde

import processing.serial.*;
Serial myPort;
int current;
float inByte;

int[] yValues;
int w;

void setup()
{
  size(640, 360);
  w = width-10;
  strokeWeight(3);
  smooth(); // or noSmooth();
  yValues = new int[w];
  String portName = Serial.list()[0];
  myPort = new Serial(this, portName, 9600);
}

void draw()
{
  // Here are simplifications possible
  // Probably with read() http://processing.org/reference/libraries/serial/Serial_read_.html
  // And get rid of this String-Stuff
  String inString = myPort.readStringUntil('\n');

  if (inString != null) {
    inString = trim(inString);
    inByte = float(inString);
    current = int(map(inByte, 0, 1023, 0, height));

    background(55);

    for (int i = 1; i < w; i++) {
      yValues[i-1] = yValues[i];
    }

    yValues[w-1] = current;

    stroke(255, 200, 0);
    line(w, current, width, current);
    strokeWeight(1);
    line(0, current, width, current);
    strokeWeight(3);

    for (int i=1; i<w; i++) {
      stroke(220, 75, yValues[i]);
      point(i, yValues[i]);
    }
  }
}