void draw() {
  /* ... */
  drawGui();
  surface.setTitle(String.format("%.2f", frameRate));
}

// Call at end of draw call so it stays on top of all else.
void drawGui() {
  resetMatrix();
  pushStyle();
  textSize(20.0);
  fill(255.0);
  // Double escape percent-sign so it isn't misinterpreted.
  text(String.format("HP: %.0f%%", 100 * 432/float(999)), 25.0, 25.0);
  popStyle();
}