ImageButtons button;
  
  void setup()
  {
    size(200, 200);
    background(102, 102, 102);
    
    // Define and create image button
    PImage b = loadImage("base.gif");
    PImage r = loadImage("roll.gif");
    PImage d = loadImage("down.gif");
    int x = width/2 - b.width/2;
    int y = height/2 - b.height/2; 
    int w = b.width;
    int h = b.height;
    button = new ImageButtons(x, y, w, h, b, r, d);
  }
  
  void draw()
  {
    button.update();
    button.display();
  }
  
  class Button
  {
    int x, y;
    int w, h;
    color basecolor, highlightcolor;
    color currentcolor;
    boolean over = false;
    boolean pressed = false;   
    
    void pressed() {
      if(over && mousePressed) {
        pressed = true;
      } else {
        pressed = false;
      }    
    }
    
    boolean overRect(int x, int y, int width, int height) {
    if (mouseX >= x && mouseX <= x+width && 
        mouseY >= y && mouseY <= y+height) {
      return true;
    } else {
      return false;
    }
  }
  }
  
  class ImageButtons extends Button 
  {
    PImage base;
    PImage roll;
    PImage down;
    PImage currentimage;
  
    ImageButtons(int ix, int iy, int iw, int ih, PImage ibase, PImage iroll, PImage idown) 
    {
      x = ix;
      y = iy;
      w = iw;
      h = ih;
      base = ibase;
      roll = iroll;
      down = idown;
      currentimage = base;
    }
    
    void update() 
    {
      over();
      pressed();
      if(pressed) {
        currentimage = down;
      } else if (over){
        currentimage = roll;
      } else {
        currentimage = base;
      }
    }
    
    void over() 
    {
      if( overRect(x, y, w, h) ) {
        over = true;
      } else {
        over = false;
      }
    }
    
    void display() 
    {
      image(currentimage, x, y);
    }
  }