Most, hogy már van gombunk, készítsünk egy újat / fejlesszük tovább a 
MainScene osztályt, úgy, hogy legyen kirakva a a képernyőre néhány gomb,
és amikor rákattintunk egyre, akkor hívassunk meg egy függvényt,
magában a MainScene osztályban.

|---------------------------------------------------------------------------------------|
| class MainScene : public Scene                                                        |
|---------------------------------------------------------------------------------------|
| + void event(const SDL_Event &ev)                                                     |
| + void update(float delta)                                                            |
| + void render()                                                                       |
|                                                                                       |
|  -----------------------------------------------------------------                    |
| | A.Verzió:                                                      |                    |
| | + static void on_first_button_clicked()                        |                    |
| |     ------------------------------------------------           |                    |
| | B Verzióhoz:                                                   |                    |
| | + static void on_first_button_clicked_member(void* cls)        |                    |
| ------------------------------------------------------------------                    |
|                                                                                       |
| + member_print()                                                                      | 
|                                                                                       |
| + MainScene()                                                                         |
| + ~MainScene()                                                                        |
|                                                                                       |
| + Camera *_camera                                                                     |
| + Image *_image                                                                       |
| + Texture *_texture                                                                   |
| + Sprite *_sprite                                                                     |
|                                                                                       |
| + Button * b1                                                                         |
| + Button * b2                                                                         |
| + Button * b3                                                                         |
|---------------------------------------------------------------------------------------|

A pszeudokód:

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void event(const SDL_Event &ev):
	b1->event(ev)
	b2->event(ev)
	b3->event(ev)

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void update(float delta):
	return

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void render():
	Renderer::get_singleton()->clear()

	_camera->bind()

	b1->render()
	b2->render()
	b3->render()

----------------------------------------------------------------------------

void on_first_button_clicked():
	printf("Click!\n")

----------------------------------------------------------------------------

void on_first_button_clicked_member(void* cls):
	if (cls):
		reinterpret_cast<MainScene*>(cls)->member_print()
	
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void member_print():
	printf("Click Member!\n")

----------------------------------------------------------------------------

MainScene():
	_camera = new Camera()
	_image = new Image("ti.bmp")
	_texture = new Texture(_image)

	b1 = new Button()
	b1->transform = Rect2(0, 0, 100, 100)
	b1->up = new Sprite(_texture)
	b1->down = new Sprite(_texture, Color(100, 100, 100))
	b1->hover = new Sprite(_texture, Color(200, 200, 200))
	//a verzió alap:
	//b1->on_click = MainScene::on_first_button_clicked;
	
	//a verzió lambda 1:
	//b1->on_click = []() -> void { printf("Click lambda!"); };

	//a verzió lambda 2:
	b1->on_click = [this]() -> void { this->member_print(); };

	b2 = new Button()
	b2->transform = Rect2(0, 110, 100, 100)
	b2->off = new Sprite(_texture, Color(50, 50, 50))
	b2->state = Button::BUTTON_STATE_OFF

	b3 = new Button()
	b3->transform = Rect2(0, 220, 100, 100)
	b3->up = new Sprite(_texture)
	b3->down = new Sprite(_texture, Color(100, 100, 100))
	b3->hover = new Sprite(_texture, Color(200, 200, 200))
	b3->cls = this
	b3->on_click_member = on_first_button_clicked_member

----------------------------------------------------------------------------

~MainScene():
	_texture->free()
	_image->free()

	delete b1->up
	delete b1->down
	delete b1->hover
	delete b1

	delete b2->off
	delete b2

	delete b3->up
	delete b3->down
	delete b3->hover
	delete b3

	delete _texture
	delete _image
	delete _camera

----------------------------------------------------------------------------