Using a BOOLEAN Variable to Store a Button State

// button variables
int buttonw = 30;
int buttonh = 20;
int buttonx = 20;
int buttony = 50;

boolean buttonON = false;

void setup()
{
  size(300, 300);  
}

void draw()
{
  if (buttonON) {
    fill(180);    
  }
  else {
    fill(0); 
  }
  rect(buttonx, buttony, buttonw, buttonh);
}


void mouseReleased()
{
  if (insideRect(mouseX, mouseY, buttonx, buttony, buttonw, buttonh)) {

    // there are multiple ways to write this operation
    //1 
    buttonON = !buttonON;            

    //2
    //  buttonON = buttonON == false ? true : false; // 

    //3
    //    if (buttonON) {
    //      buttonON = false;
    //    } 
    //    else {
    //      buttonOON = true;
    //    }
    //
    //
  }    
}


// boolean function returns either true or false 
// if an x,y point is inside a rectanglular area
boolean insideRect(float px, float py, float rx, float ry, float rw, float rh) {
  return px >= rx && px <= rx+rw && py >= ry && py <= ry+rh;
}