// processing IDE 3.5.3
// button tutorial 
// http://kll.engineering-news.org/kllfusion01/articles.php?article_id=166
// the word hardcoded means instead using variables for position x,y,w,h,...
// direct first try usually is to use pix positions.

// you do several of this buttons and learn ( the hard way ) that you need hundred of code lines 
// and easy get lost if need searching on errors.
 
// but THIS is our tutorial START:
// a functioning toggle button

boolean sel = false;

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

void draw() {
  background(200, 200, 0);
  if (sel)   fill(0, 200, 0);
  else       fill(0, 0, 200);
  if (mouseX > 100 & mouseX < 180 & mouseY > 100 & mouseY < 130) stroke(200, 0, 200);
  else                                                           stroke(0, 200, 200);
  strokeWeight(3);
  rect(100, 100, 80, 30);
  noStroke();
  fill(200);
  text("press", 110, 120);
}

void mousePressed() {
  if (mouseX > 100 & mouseX < 180 & mouseY > 100 & mouseY < 130)  sel = !sel; // button action
}