int x;
boolean changed_unexpectedly;

void setup()
{
  size(128, 128);
  textFont(createFont("SansSerif", 12));
  fill(255, 255, 255);
  noLoop();
}

void draw()
{
  if (changed_unexpectedly)
    return;
  background(0);
 
  int x_before = x;
  text(str(x_before), 0, 16);
  
  /* waste some time */
  for (int i = 0; i < 100000; i++)
    rect(48,16,16,16);

  int x_after = x; 
  text(str(x_after), 0, 32);

  if (x_before != x_after)
  {
    changed_unexpectedly = true;
    text("Changed", 0, 48);
  }
}
  
void keyPressed()
{
  if (changed_unexpectedly)
    return;
  x++;
  redraw();
}