Simple GImage Button

//libraries demo

//import necessary libraries
import g4p_controls.*;

//declare necessary variables
PImage photo;
GImageButton myButton;
String [] files;
float startTime;
boolean startScreen;
color bgColor;


void setup () {
  size (2560, 1600);
  //boolean to keep track of which screen draws
  startScreen = true;
  photo = loadImage("firewatch.jpg");
  //string array to store file names of button states
  files = new String [] {"Up.png", "Hover.png", "Down.png",};
  //instantiate new button (note that it takes files, the string array, as an argument)
  myButton = new GImageButton (this, width/2-600, height/2-600, files);
}
void draw () {
  if(startScreen) {
  background (photo);
  } else {
    background (0, 100, 200);
    fill ((millis()-startTime)/10*255/width, 50, 50);
    rect ((millis()-startTime)/10, height/2,100,100);
  }
}
//necessary function when using G4P
void handleButtonEvents (GImageButton button, GEvent event) {
  if (button==myButton){
    //all code that covers what we want to happen when button is pressed
    println ("Button Pressed");
    myButton.dispose();
    myButton=null;
    startScreen=false;
    startTime = millis();
  }
}