float buttonX, buttonY;  //// Position Of Button
float horizon;
int value=100;

//// Size 
void setup() {
  size(600,600);
}
//// Color Of Background 
void draw() {
  background(value);
  cursor(CROSS);
  fill(200);
  stroke(2);
  rectMode(CENTER);
  rect(100,100, 100,50);
}


void button() {
 float buttonX=50, buttonY=50, buttonW=100, buttonH=100;
/// Button
 fill( 200 );
 stroke(1);
 rectMode(CENTER);
 
 rect(100,100, 50,50);
}
//// Handlers; keys & clicks

void keyPressed() {
  if (key == 'q') exit();
}

void mousePressed() {
  if ( value == 100 ) {
   value = 255;
  } else {
   value = 100;
  } 
}