godot-docs/tutorials/step_by_step/simple_2d_game.rst

.. _doc_simple_2d_game:

Simple 2D game
==============

Pong
~~~~

In this simple tutorial, a basic game of Pong will be created. There are
plenty of more complex examples in the demos included with the engine,
but this should get introduced to basic functionality for 2D Games.

Assets
~~~~~~

Some assets are included for this tutorial:
:download:`pong_assets.zip </files/pong_assets.zip>`.

Scene setup
~~~~~~~~~~~

For the sake of the old times, the game will be in 640x400 pixels
resolution. This can be configured in the Project Settings (see :ref:`doc_scenes_and_nodes-configuring_the_project`). The default background color should be set to black:

.. image:: /img/clearcolor.png

Create a :ref:`class_Node2D` node for the project root. Node2D is the base
type for the 2D engine. After this, add some sprites :ref:`class_Sprite`
node) and set each to the corresponding texture. The final scene layout
should look similar to this (note: the ball is in the middle!):

.. image:: /img/pong_layout.png

The scene tree should, then, look similar to this:

.. image:: /img/pong_nodes.png

Save the scene as "pong.scn" and set it as the main scene in the project
properties.

Input actions setup
~~~~~~~~~~~~~~~~~~~

There are so many input methods for video games... Keyboard, Joypad,
Mouse, Touchscreen (Multitouch). Yet this is pong. The only input that
matters is for the pads going up and down.

Handling all possible input methods can be very frustrating and take a
lot of code. The fact that most games allow controller customization
makes this worse. For this, Godot created the "Input Actions". An action
is defined, then input methods that trigger it are added.

Open the project properties dialog again, but this time move to the
"Input Map" tab.

On it, add 4 actions:
"left_move_up","left_move_down","right_move_up","right_move_down".
Assign the keys that you desire. A/Z for left and Up/Down as keys
should work in most cases.

.. image:: /img/inputmap.png

Script
~~~~~~

Create a script for the root node of the scene and open it (as explained
in :ref:`doc_scripting-adding_a_script`). The script will inherit Node2D:

::

    extends Node2D

    func _ready():
        pass

In the constructor, two things will be done. The first is to enable
processing, and the second to store some useful values. Such values are
the dimensions of the screen and the pad:

::


    extends Node2D

    var screen_size
    var pad_size

    func _ready():
        screen_size = get_viewport_rect().size
        pad_size = get_node("left").get_texture().get_size()
        set_process(true)

Then, some variables used for in-game will be added:

::

    #speed of the ball (in pixels/second0

    var ball_speed = 80
    #direction of the ball (normal vector)

    var direction = Vector2(-1,0)
    #constant for pad speed (also in pixels/second)

    const PAD_SPEED = 150

Finally, the process function:

::

    func _process(delta):

Get some useful values for computation. The first is the ball position
(from the node), the second is the rectangles (Rect2) of the pads.
Sprites by defaut center the textures, so a small adjustment of size/2
must be added.

::

        var ball_pos = get_node("ball").get_pos()
        var left_rect = Rect2( get_node("left").get_pos() - pad_size/2, pad_size )
        var right_rect = Rect2( get_node("right").get_pos() - pad_size/2, pad_size )

Since the ball pos was obtained, integrating it should be simple:

::

        ball_pos+=direction*ball_speed*delta

Then, now that the ball has a new position, it should be tested against
everything. First, the floor and the roof:

::

        if ( (ball_pos.y<0 and direction.y <0) or (ball_pos.y>screen_size.y and direction.y>0)):
            direction.y = -direction.y

If one of the pads was touched, change direction and increase speed a
little.

::

        if ( (left_rect.has_point(ball_pos) and direction.x < 0) or (right_rect.has_point(ball_pos) and direction.x > 0)):
            direction.x=-direction.x
            ball_speed*=1.1
            direction.y=randf()*2.0-1
            direction = direction.normalized()

If the ball went out of the screen, it's game over. Game restarts:

::

        if (ball_pos.x<0 or ball_pos.x>screen_size.x):
            ball_pos=screen_size*0.5 #ball goes to screen center
            ball_speed=80
            direction=Vector2(-1,0)

Once everything was done with the ball, the node is updated with the new
position:

::

        get_node("ball").set_pos(ball_pos)

Only updating the pads according to player input. the Input class is
really useful here:

::

        #move left pad  
        var left_pos = get_node("left").get_pos()

        if (left_pos.y > 0 and Input.is_action_pressed("left_move_up")):
            left_pos.y+=-PAD_SPEED*delta
        if (left_pos.y < screen_size.y and Input.is_action_pressed("left_move_down")):
            left_pos.y+=PAD_SPEED*delta

        get_node("left").set_pos(left_pos)

        #move right pad 
        var right_pos = get_node("right").get_pos()

        if (right_pos.y > 0 and Input.is_action_pressed("right_move_up")):
            right_pos.y+=-PAD_SPEED*delta
        if (right_pos.y < screen_size.y and Input.is_action_pressed("right_move_down")):
            right_pos.y+=PAD_SPEED*delta

        get_node("right").set_pos(right_pos)

And that's it! A simple Pong was written with a few lines of code.