class Button : TaggedObject, Drawable, Updatable {
  vec2i pos; string text;
  vec2i to;
  float delegate(TransitionMode) dg;
  vec4f fill;
  void delegate() onClick;
  void init(string s, vec2i p, void delegate() dg) {
    (text, pos, onClick) = (s, p, dg);
    this.dg = genTransition(0, 1, transferTime => 0.3);
    fill = vec4f(0.2, 0.4, 0.8, 0.7);
  }
  string ident() return "Button";
  Tag offers(string s) {
    if s == "Button" || s == "Drawable" || s == "Updatable" return this;
    return super.offers s;
  }
  void draw() {
    auto leaf = parseText text;
    auto h = printAt(overlay, pos, leaf, width => 90, radius => 7, fill => fill);
    to = pos + vec2i(90, h);
  }
  void update(void delegate(Drawable) addDrawable) {
    bool inside, active;
    if (mouse-pos.(x >= pos.x && y >= pos.y && x < to.x && y < to.y)) {
      inside = true;
      if mouse-released onClick();
      if mouse-pressed active = true;
    }
    auto factor = dg([TransitionMode.Down, TransitionMode.Up][inside]);
    fill = vec4f(0.2, 0.4, 0.8, 0.6) * (1 - factor)
         + vec4f(0.2, 0.4, 0.8, [float:0.8, 1][active]) * factor;
  }
}