Code

import controlP5.*;
import processing.serial.*;
import gohai.glvideo.*;
GLCapture video;
ControlP5 cp5;
//Capture cam;
Serial ser;

String username, password; //destID = "SYS", sourceID = "GUI"
float waterLevel = 0;
int level = 0;
PImage bg;
public void setup() {
  size(800, 480, P2D);
  bg = loadImage("apss.jpg");
  //GUI Library
  cp5 = new ControlP5(this);
  // for RPI Camera
  video = new GLCapture(this, 0);
  video.play();
  //Serial initizalization
  String portName = Serial.list()[0];
  ser = new Serial(this, portName, 9600);
  login();
}

void draw() {
  background(bg);
}
/////////////////////////////
/*********GUI*******/
////////////////////////////

public void login() {
  cp5.addTextfield("USERNAME").setPosition(100, 150).setSize(200, 40).setAutoClear(false);
  cp5.addTextfield("PASSWORD").setPosition(100, 220).setSize(200, 40).setAutoClear(false);
  cp5.addBang("Submit").setPosition(160, 290).setSize(80, 40);
}

public void Submit() {
  username = cp5.get(Textfield.class, "USERNAME").getText();
  password = cp5.get(Textfield.class, "PASSWORD").getText();
  //cp5.setAutoDraw(false);
  if ( username.equals("SYS") && password.equals("flash") ) {
    clear();
    mainGUI();
    enquiry();
    checkSerial();
  } else {
    println("Wrong username or password.");
  }
}

public void mainGUI() {
  cp5.get("USERNAME").hide();
  cp5.get("PASSWORD").hide();
  cp5.get("Submit").hide();
  cp5.addBang("Feed").setPosition(50, 75).setSize(200, 60);
  cp5.addBang("Bath").setPosition(300, 75).setSize(200, 60);
  cp5.addBang("Camera").setPosition(550, 75).setSize(200, 60);
  cp5.addBang("Level").setPosition(50, 195).setSize(200, 60);
  cp5.addBang("Clean").setPosition(300, 195).setSize(200, 60);
  cp5.addBang("Light").setPosition(550, 195).setSize(200, 60);
  cp5.addBang("Temperature").setPosition(300, 315).setSize(200, 60);
}


public void Feed() {
  mode = "";
  mode+="FEED";
  writeData();
  println(data);
}
public void Bath() {
  mode = "";
  mode+="BATH";
  writeData();
  println(data);
}
public void Level() {
  mode = "";
  mode+="LVEL";
  writeData();
  println(data);

  cp5.get("USERNAME").hide();
  cp5.get("PASSWORD").hide();
  cp5.get("Submit").hide();
  cp5.get("Feed").hide();
  cp5.get("Bath").hide();
  cp5.get("Camera").hide();
  cp5.get("Level").hide();
  cp5.get("Clean").hide();
  cp5.get("Light").hide();
  cp5.addBang("Food").setPosition(360, 120).setSize(80, 40);
  cp5.addBang("Water").setPosition(360, 190).setSize(80, 40);
  cp5.addBang("Back").setPosition(700, 400).setSize(80, 40);
}
public void Food() {
  checkLevel();
}
public void Water() {
  checkLevel();
}

public void Camera() {
  cp5.get("USERNAME").hide();
  cp5.get("PASSWORD").hide();
  cp5.get("Submit").hide();
  cp5.get("Feed").hide();
  cp5.get("Bath").hide();
  cp5.get("Camera").hide();
  cp5.get("Level").hide();
  cp5.get("Clean").hide();
  cp5.get("Light").hide();
  if (video.available()) {
    video.read();
  }
  image(video, 0, 0, width, height);
}

public void Clean() {
  mode = "";
  mode+="CLIN";
  writeData();
}
public void Temperature() {
  mode = "";
  mode+="TEMP";
  writeData();
  println(data);
}
public void Light() {
  cp5.get("USERNAME").hide();
  cp5.get("PASSWORD").hide();
  cp5.get("Submit").hide();
  cp5.get("Feed").hide();
  cp5.get("Bath").hide();
  cp5.get("Camera").hide();
  cp5.get("Level").hide();
  cp5.get("Clean").hide();
  cp5.get("Light").hide();
  cp5.addBang("LightOff").setPosition(360, 120).setSize(80, 40);
  cp5.addBang("LightOn").setPosition(360, 190).setSize(80, 40);
  cp5.addBang("Back").setPosition(700, 400).setSize(80, 40);
}
public void LightOff() {
  mode = "";
  mode+="LGHF";
  writeData();
  println(data);
}
public void LightOn() {
  mode = "";
  mode+="LGHT";
  writeData();
}
public void Back() {
  cp5.get("Feed").show();
  cp5.get("Bath").show();
  cp5.get("Camera").show();
  cp5.get("Level").show();
  cp5.get("Clean").show();
  cp5.get("Light").show();
  cp5.get("LightOff").hide();
  cp5.get("LightOn").hide();
  cp5.get("Back").hide();
}

public void checkLevel() {

  if (ser.available() > 0) {
    level = ser.read();
    println(level);
  }
  // Draw the Level
  noStroke();
  fill(0, 0, 255);
  rect(160, 390 - waterLevel, 480, waterLevel);

  // Draw the container
  stroke(255);
  strokeWeight(2.0);
  noFill();
  rect(160, 90, 480, 300);

  waterLevel = level;
}

///////////////////////////////
////// COMMUNICATIONS ////////
//////////////////////////////

byte SOH = 0x02;
byte SOT = 0x07;
byte EOH = 0x04;
byte EOT = 0x09;
byte ENQ = 0x05;
byte ACK = 0x06;
byte NAK = 0x21;
String destID = "SYS";
String srcID = "GUI";
String pass = "flash";
String data = "";
String SOHh = Integer.toHexString(SOH);
String SOTh = Integer.toHexString(SOT);
String EOTh = Integer.toHexString(EOT);
String EOHh = Integer.toHexString(EOH);
String ENQh = Integer.toHexString(ENQ);
String ACKh = Integer.toHexString(ACK);
String NAKh = Integer.toHexString(NAK);
String mode = "";
String checkSer;

////////////////////////
String CRCPoly = "11000000000000101";
public void checkSerial() {
  while (ser.available() > 0) {
    checkSer = ser.readString();
  } //***CHECK
  if (checkSer.equals("ACK") {
    println("REQUEST ACKNOWLEDGED. COMMUNICATION ESTABLISHED!");
  } else {
    if (checkSer.equals("NAK")) {
      println("RECEIVER IS BUSY.");
      delay(500);
      enquiry();
    } else if (checkSer.equals("CDATA")) {
      println("CORRECT DATA WAS SENT!");
    } else if (checkSer.equals("WRNME")) {
      println("WRONG USERNAME AND SOURCE ID");
      println("DATA HAS ERRORS, RETRANSMITTING DATA");
      delay(500);
      buildFrame();
    } else if (checkSer.equals("WRPASS")) {
      println("INCORRECT PASSWORD, BREACHING OCCURS.");
      println("DATA HAS ERRORS, RETRANSMITTING DATA");
      delay(500);
      buildFrame();
    } else if (checkSer.equals("WRCRC")) {
      println("INCORRECT CRC, RECOMPUTING..");
      println("DATA HAS ERRORS, RETRANSMITTING DATA");
      delay(500);
      buildFrame();
    }
  }
}
public void enquiry() {
  ser.write("ENQ");
}


public void writeData() {
  println(data);
  ser.write(data);
}
public void buildFrame() {
  data = ""; //CLEAR PREVIOUS DATA
  data+=SOHh;
  data+=destID;
  data+=srcID;
  data+=pass;
  data+=SOTh;
  data+=mode;
  data+=EOTh;
  String CRC = compCRC();
  data+=CRC;
  data+=EOHh;
}

public String compCRC() {
  byte[] y  = mode.getBytes();
  String a = binary(y[0], 8);
  String b = binary(y[1], 8);
  String c = binary(y[2], 8);
  String d = binary(y[3], 8);
  String abcd = a+b+c+d+"0000000000000000";
  String got= "", recX, finalget1="", finalget2 = "";
  char CRCOUT1 = 0, CRCOUT2 = 0;
  int rGot, rPoly, xorMo=0;
  int c1 = 0, c2 = 17;
  rPoly = unbinary(CRCPoly);
  while (c2<49) {
    got = abcd.substring(c1, c2);
    //print(got);
    char getc = got.charAt(0);
    if (getc=='0') {
      c1++;
      c2++;
    } else if (getc=='1') {
      rGot = unbinary(got);
      xorMo= rGot^rPoly;
      recX = binary(xorMo, 17);
      abcd = abcd.replaceFirst(got, recX);
      //println("abcd is " +abcd);
    }
  }
  finalget1 = abcd.substring(32, 40);
  finalget2 = abcd.substring(40, 48);
  CRCOUT1 = char(unbinary(finalget1));
  CRCOUT2 = char(unbinary(finalget2));
  char xa = CRCOUT1;
  char xb = CRCOUT2;
  String xc = Character.toString(xa);
  String xd = Character.toString(xb);
  String res = xc+xd;
  return res;
}