Coding the player

In this lesson, we'll add player movement, animation, and set it up to detect collisions.

To do so, we need to add some functionality that we can't get from a built-in node, so we'll add a script. Click the Player node and click the "Attach Script" button:

In the script settings window, you can leave the default settings alone. Just click "Create":

Note

If you're creating a C# script or other languages, select the language from the language drop down menu before hitting create.

Note

If this is your first time encountering GDScript, please read Scripting languages before continuing.

Start by declaring the member variables this object will need:

GDScriptC#C++

extends Area2D

export var speed = 400 # How fast the player will move (pixels/sec).
var screen_size # Size of the game window.

Using the export keyword on the first variable speed allows us to set its value in the Inspector. This can be handy for values that you want to be able to adjust just like a node's built-in properties. Click on the Player node and you'll see the property now appears in the "Script Variables" section of the Inspector. Remember, if you change the value here, it will override the value written in the script.

Warning

If you're using C#, you need to (re)build the project assemblies whenever you want to see new export variables or signals. This build can be manually triggered by clicking the word "Mono" at the bottom of the editor window to reveal the Mono Panel, then clicking the "Build Project" button.

The _ready() function is called when a node enters the scene tree, which is a good time to find the size of the game window:

GDScriptC#C++

func _ready():
    screen_size = get_viewport_rect().size

Now we can use the _process() function to define what the player will do. _process() is called every frame, so we'll use it to update elements of our game, which we expect will change often. For the player, we need to do the following:

• Check for input.

• Move in the given direction.

• Play the appropriate animation.

First, we need to check for input - is the player pressing a key? For this game, we have 4 direction inputs to check. Input actions are defined in the Project Settings under "Input Map". Here, you can define custom events and assign different keys, mouse events, or other inputs to them. For this game, we will map the arrow keys to the four directions.

Click on Project -> Project Settings to open the project settings window and click on the Input Map tab at the top. Type "move_right" in the top bar and click the "Add" button to add the move_right action.

We need to assign a key to this action. Click the "+" icon on the right, then click the "Key" option in the drop-down menu. A dialog asks you to type in the desired key. Press the right arrow on your keyboard and click "Ok".

Repeat these steps to add three more mappings:

1. move_left mapped to the left arrow key.

2. move_up mapped to the up arrow key.

3. And move_down mapped to the down arrow key.

Your input map tab should look like this:

Click the "Close" button to close the project settings.

Note

We only mapped one key to each input action, but you can map multiple keys, joystick buttons, or mouse buttons to the same input action.

You can detect whether a key is pressed using Input.is_action_pressed(), which returns true if it's pressed or false if it isn't.

GDScriptC#C++

func _process(delta):
    var velocity = Vector2.ZERO # The player's movement vector.
    if Input.is_action_pressed("move_right"):
        velocity.x += 1
    if Input.is_action_pressed("move_left"):
        velocity.x -= 1
    if Input.is_action_pressed("move_down"):
        velocity.y += 1
    if Input.is_action_pressed("move_up"):
        velocity.y -= 1

    if velocity.length() > 0:
        velocity = velocity.normalized() * speed
        $AnimatedSprite.play()
    else:
        $AnimatedSprite.stop()

We start by setting the velocity to (0, 0) - by default, the player should not be moving. Then we check each input and add/subtract from the velocity to obtain a total direction. For example, if you hold right and down at the same time, the resulting velocity vector will be (1, 1). In this case, since we're adding a horizontal and a vertical movement, the player would move faster diagonally than if it just moved horizontally.

We can prevent that if we normalize the velocity, which means we set its length to 1, then multiply by the desired speed. This means no more fast diagonal movement.

Tip

If you've never used vector math before, or need a refresher, you can see an explanation of vector usage in Redot at Vector math. It's good to know but won't be necessary for the rest of this tutorial.

We also check whether the player is moving so we can call play() or stop() on the AnimatedSprite.

Tip

$ is shorthand for get_node(). So in the code above, $AnimatedSprite.play() is the same as get_node("AnimatedSprite").play().

In GDScript, $ returns the node at the relative path from the current node, or returns null if the node is not found. Since AnimatedSprite is a child of the current node, we can use $AnimatedSprite.

Now that we have a movement direction, we can update the player's position. We can also use clamp() to prevent it from leaving the screen. Clamping a value means restricting it to a given range. Add the following to the bottom of the _process function (make sure it's not indented under the else):

GDScriptC#C++

position += velocity * delta
position.x = clamp(position.x, 0, screen_size.x)
position.y = clamp(position.y, 0, screen_size.y)

Tip

The delta parameter in the _process() function refers to the frame length - the amount of time that the previous frame took to complete. Using this value ensures that your movement will remain consistent even if the frame rate changes.

Click "Play Scene" (F6, Cmd + R on macOS) and confirm you can move the player around the screen in all directions.

Warning

If you get an error in the "Debugger" panel that says

Attempt to call function 'play' in base 'null instance' on a null instance

this likely means you spelled the name of the AnimatedSprite node wrong. Node names are case-sensitive and $NodeName must match the name you see in the scene tree.

Choosing animations

Now that the player can move, we need to change which animation the AnimatedSprite is playing based on its direction. We have the "walk" animation, which shows the player walking to the right. This animation should be flipped horizontally using the flip_h property for left movement. We also have the "up" animation, which should be flipped vertically with flip_v for downward movement. Let's place this code at the end of the _process() function:

GDScriptC#C++

if velocity.x != 0:
    $AnimatedSprite.animation = "walk"
    $AnimatedSprite.flip_v = false
    # See the note below about boolean assignment.
    $AnimatedSprite.flip_h = velocity.x < 0
elif velocity.y != 0:
    $AnimatedSprite.animation = "up"
    $AnimatedSprite.flip_v = velocity.y > 0

Note

The boolean assignments in the code above are a common shorthand for programmers. Since we're doing a comparison test (boolean) and also assigning a boolean value, we can do both at the same time. Consider this code versus the one-line boolean assignment above:

GDScriptC#

if velocity.x < 0:
    $AnimatedSprite.flip_h = true
else:
    $AnimatedSprite.flip_h = false

Play the scene again and check that the animations are correct in each of the directions.

Tip

A common mistake here is to type the names of the animations wrong. The animation names in the SpriteFrames panel must match what you type in the code. If you named the animation "Walk", you must also use a capital "W" in the code.

When you're sure the movement is working correctly, add this line to _ready(), so the player will be hidden when the game starts:

GDScriptC#C++

hide()

Preparing for collisions

We want Player to detect when it's hit by an enemy, but we haven't made any enemies yet! That's OK, because we're going to use Redot's signal functionality to make it work.

Add the following at the top of the script, after extends Area2D:

GDScriptC#C++

signal hit

This defines a custom signal called "hit" that we will have our player emit (send out) when it collides with an enemy. We will use Area2D to detect the collision. Select the Player node and click the "Node" tab next to the Inspector tab to see the list of signals the player can emit:

Notice our custom "hit" signal is there as well! Since our enemies are going to be RigidBody2D nodes, we want the body_entered(body: Node) signal. This signal will be emitted when a body contacts the player. Click "Connect.." and the "Connect a Signal" window appears. We don't need to change any of these settings so click "Connect" again. Redot will automatically create a function in your player's script.

Note the green icon indicating that a signal is connected to this function. Add this code to the function:

GDScriptC#C++

func _on_Player_body_entered(body):
    hide() # Player disappears after being hit.
    emit_signal("hit")
    # Must be deferred as we can't change physics properties on a physics callback.
    $CollisionShape2D.set_deferred("disabled", true)

Each time an enemy hits the player, the signal is going to be emitted. We need to disable the player's collision so that we don't trigger the hit signal more than once.

Note

Disabling the area's collision shape can cause an error if it happens in the middle of the engine's collision processing. Using set_deferred() tells Redot to wait to disable the shape until it's safe to do so.

The last piece is to add a function we can call to reset the player when starting a new game.

GDScriptC#C++

func start(pos):
    position = pos
    show()
    $CollisionShape2D.disabled = false

With the player working, we'll work on the enemy in the next lesson.