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Listening to player input

Building upon the previous lesson Creating your first script, let's look at another important feature of any game: giving control to the player. To add this, we need to modify our sprite_2d.gd code.

You have two main tools to process the player's input in Godot:

1. The built-in input callbacks, mainly _unhandled_input(). Like _process(), it's a built-in virtual function that Godot calls every time the player presses a key. It's the tool you want to use to react to events that don't happen every frame, like pressing Space to jump. To learn more about input callbacks, see Using InputEvent.

2. The Input singleton. A singleton is a globally accessible object. Godot provides access to several in scripts. It's the right tool to check for input every frame.

We're going to use the Input singleton here as we need to know if the player wants to turn or move every frame.

For turning, we should use a new variable: direction. In our _process() function, replace the rotation += angular_speed * delta line with the code below.

GDScriptC#

var direction = 0
if Input.is_action_pressed("ui_left"):
    direction = -1
if Input.is_action_pressed("ui_right"):
    direction = 1

rotation += angular_speed * direction * delta

Our direction local variable is a multiplier representing the direction in which the player wants to turn. A value of 0 means the player isn't pressing the left or the right arrow key. A value of 1 means the player wants to turn right, and -1 means they want to turn left.

To produce these values, we introduce conditions and the use of Input. A condition starts with the if keyword in GDScript and ends with a colon. The condition is the expression between the keyword and the end of the line.

To check if a key was pressed this frame, we call Input.is_action_pressed(). The method takes a text string representing an input action and returns true if the action is pressed, false otherwise.

The two actions we use above, "ui_left" and "ui_right", are predefined in every Godot project. They respectively trigger when the player presses the left and right arrows on the keyboard or left and right on a gamepad's D-pad.

Note

You can see and edit input actions in your project by going to Project -> Project Settings and clicking on the Input Map tab.

Finally, we use the direction as a multiplier when we update the node's rotation: rotation += angular_speed * direction * delta.

If you run the scene with this code, the icon should rotate when you press Left and Right.

Moving when pressing "up"

To only move when pressing a key, we need to modify the code that calculates the velocity. Replace the line starting with var velocity with the code below.

GDScriptC#

var velocity = Vector2.ZERO
if Input.is_action_pressed("ui_up"):
    velocity = Vector2.UP.rotated(rotation) * speed

We initialize the velocity with a value of Vector2.ZERO, another constant of the built-in Vector type representing a 2D vector of length 0.

If the player presses the "ui_up" action, we then update the velocity's value, causing the sprite to move forward.

Complete script

Here is the complete sprite_2d.gd file for reference.

GDScriptC#

extends Sprite2D

var speed = 400
var angular_speed = PI


func _process(delta):
    var direction = 0
    if Input.is_action_pressed("ui_left"):
        direction = -1
    if Input.is_action_pressed("ui_right"):
        direction = 1

    rotation += angular_speed * direction * delta

    var velocity = Vector2.ZERO
    if Input.is_action_pressed("ui_up"):
        velocity = Vector2.UP.rotated(rotation) * speed

    position += velocity * delta