godot-docs/getting_started/first_2d_game/04.creating_the_enemy.rst

.. _doc_your_first_2d_game_creating_the_enemy:

Creating the enemy
==================

Now it's time to make the enemies our player will have to dodge. Their behavior
will not be very complex: mobs will spawn randomly at the edges of the screen,
choose a random direction, and move in a straight line.

We'll create a ``Mob`` scene, which we can then *instance* to create any number
of independent mobs in the game.

Node setup
~~~~~~~~~~

Click Scene -> New Scene from the top menu and add the following nodes:

- :ref:`RigidBody2D <class_RigidBody2D>` (named ``Mob``)

   - :ref:`AnimatedSprite2D <class_AnimatedSprite2D>`
   - :ref:`CollisionShape2D <class_CollisionShape2D>`
   - :ref:`VisibleOnScreenNotifier2D <class_VisibleOnScreenNotifier2D>`

Don't forget to set the children so they can't be selected, like you did with
the Player scene.

In the :ref:`RigidBody2D <class_RigidBody2D>` properties, set ``Gravity Scale``
to ``0``, so the mob will not fall downward. In addition, under the
:ref:`CollisionObject2D <class_CollisionObject2D>` section, uncheck the ``1`` inside the ``Mask`` property.
This will ensure the mobs do not collide with each other.

.. image:: img/set_collision_mask.webp

Set up the :ref:`AnimatedSprite2D <class_AnimatedSprite2D>` like you did for the
player. This time, we have 3 animations: ``fly``, ``swim``, and ``walk``. There
are two images for each animation in the art folder.

The ``Animation Speed`` property has to be set for each individual animation. Adjust it to ``3`` for all 3 animations.

.. image:: img/mob_animations.webp

You can use the "Play Animation" buttons on the right of the ``Animation Speed`` input field to preview your animations.

We'll select one of these animations randomly so that the mobs will have some
variety.

Like the player images, these mob images need to be scaled down. Set the
``AnimatedSprite2D``'s ``Scale`` property to ``(0.75, 0.75)``.

As in the ``Player`` scene, add a ``CapsuleShape2D`` for the collision. To align
the shape with the image, you'll need to set the ``Rotation Degrees`` property
to ``90`` (under "Transform" in the Inspector).

Save the scene.

Enemy script
~~~~~~~~~~~~

Add a script to the ``Mob`` like this:

.. tabs::
 .. code-tab:: gdscript GDScript

    extends RigidBody2D

 .. code-tab:: csharp

    using Godot;

    public partial class Mob : RigidBody2D
    {
        // Don't forget to rebuild the project.
    }

 .. code-tab:: cpp

    // Copy `player.gdns` to `mob.gdns` and replace `Player` with `Mob`.
    // Attach the `mob.gdns` file to the Mob node.

    // Create two files `mob.cpp` and `mob.hpp` next to `entry.cpp` in `src`.
    // This code goes in `mob.hpp`. We also define the methods we'll be using here.
    #ifndef MOB_H
    #define MOB_H

    #include <AnimatedSprite2D.hpp>
    #include <Godot.hpp>
    #include <RigidBody2D.hpp>

    class Mob : public godot::RigidBody2D {
        GODOT_CLASS(Mob, godot::RigidBody2D)

        godot::AnimatedSprite2D *_animated_sprite;

    public:
        void _init() {}
        void _ready();
        void _on_visible_on_screen_notifier_2d_screen_exited();

        static void _register_methods();
    };

    #endif // MOB_H

Now let's look at the rest of the script. In ``_ready()`` we play the animation
and randomly choose one of the three animation types:

.. tabs::
 .. code-tab:: gdscript GDScript

    func _ready():
        var mob_types = $AnimatedSprite2D.sprite_frames.get_animation_names()
        $AnimatedSprite2D.play(mob_types[randi() % mob_types.size()])

 .. code-tab:: csharp

    public override void _Ready()
    {
        var animatedSprite2D = GetNode<AnimatedSprite2D>("AnimatedSprite2D");
        string[] mobTypes = animatedSprite2D.SpriteFrames.GetAnimationNames();
        animatedSprite2D.Play(mobTypes[GD.Randi() % mobTypes.Length]);
    }

 .. code-tab:: cpp

    // This code goes in `mob.cpp`.
    #include "mob.hpp"

    #include <RandomNumberGenerator.hpp>
    #include <SpriteFrames.hpp>

    void Mob::_ready() {
        godot::Ref<godot::RandomNumberGenerator> random = godot::RandomNumberGenerator::_new();
        _animated_sprite = get_node<godot::AnimatedSprite2D>("AnimatedSprite2D");
        _animated_sprite->set_playing(true);
        godot::PoolStringArray mob_types = _animated_sprite->get_sprite_frames()->get_animation_names();
        _animated_sprite->set_animation(mob_types[random->randi() % mob_types.size()]);
    }

First, we get the list of animation names from the AnimatedSprite2D's ``frames``
property. This returns an Array containing all three animation names: ``["walk",
"swim", "fly"]``.

We then need to pick a random number between ``0`` and ``2`` to select one of
these names from the list (array indices start at ``0``). ``randi() % n``
selects a random integer between ``0`` and ``n-1``.

The last piece is to make the mobs delete themselves when they leave the screen.
Connect the ``screen_exited()`` signal of the ``VisibleOnScreenNotifier2D`` node
to the ``Mob`` and add this code:

.. tabs::
 .. code-tab:: gdscript GDScript

    func _on_visible_on_screen_notifier_2d_screen_exited():
        queue_free()

 .. code-tab:: csharp

    private void OnVisibleOnScreenNotifier2DScreenExited()
    {
        QueueFree();
    }

 .. code-tab:: cpp

    // This code goes in `mob.cpp`.
    void Mob::_on_visible_on_screen_notifier_2d_screen_exited() {
        queue_free();
    }

This completes the `Mob` scene.

With the player and enemies ready, in the next part, we'll bring them together
in a new scene. We'll make enemies spawn randomly around the game board and move
forward, turning our project into a playable game.