How to create a simple 3D scene
=================================

In this tutorial we will go throught the example **example_7_cameraSystem.py** where we will build a scene with two cubes and a camera.

The final result looks like this:

.. image:: img/cubesExample.png
    :align: center


Create the scene and the camera
--------------------------------------

The code below creates the scene and adds a camera

.. code-block:: python

    # Scenegraph with Entities, Components
    rootEntity = scene.world.createEntity(Entity(name="Root"))

    # Spawn Camera
    mainCamera = SimpleCamera("Simple Camera");


As you see we currently have only a single Entity to our scene. The camera is a system, it traverses the scene to render the content with the code below

.. code-block:: python

    scene.world.traverse_visit_pre_camera(camUpdate, mainCamera.camera)


Create the cube
------------------

Now lets add some cubes to the scene

.. code-block:: python

    cube_bot: GameObjectEntity = CubeSpawn("BOT CUBE")
    scene.world.addEntityChild(home1, cube_bot);
    cube_top: GameObjectEntity = CubeSpawn()


This code block creates a cube entity and adds it to the scene under the "home1" entity. The :code:`CubeSpawn()` method initializes the vertices of our cube.


.. image:: img/scenegraph.png
    :align: center

As you can see in the image above, this is the scenegraph hierarchy. All the entities and components are visible.

Put it all together
--------------------

In the main game loop we are doing the following

1. Traversing all the objects and update their transformations

.. code-block:: python

    scene.world.traverse_visit(transUpdate, scene.world.root) 

2. Update our camera. We can also manipulate the camera using real-time GUIs

.. code-block:: python

    scene.world.traverse_visit_pre_camera(camUpdate, mainCamera.camera)
    scene.world.traverse_visit(camUpdate, scene.world.root)

3. Call the :code:`renderUpdate` system to render the scene

.. code-block:: python

    scene.world.traverse_visit(renderUpdate, scene.world.root)

.. note:: 
    
    Keep in mind that the :code:`transUpdate`, the :code:`camUpdate` and the :code:`renderUpdate` are systems.
    The :code:`traverse_visit` method visits all the entities of our scenegraph and applies the given system when applicable.