GDScript

Introduction

GDScript is a high level, dynamically typed programming language used to create content. It uses a syntax similar to Python (blocks are indent-based and many keywords are similar). Its goal is to be optimized for and tightly integrated with Godot Engine, allowing great flexibility for content creation and integration.

History

Initially, Godot was designed to support multiple scripting languages (this ability still exists today). However, only GDScript is in use right now. There is a little history behind this.

In the early days, the engine used the Lua scripting language. Lua is fast, but creating bindings to an object oriented system (by using fallbacks) was complex and slow and took an enormous amount of code. After some experiments with Python, it also proved difficult to embed.

The last third party scripting language that was used for shipped games was Squirrel, but it was dropped as well. At that point, it became evident that a custom scripting language could more optimally make use of Godot’s particular architecture:

  • Godot embeds scripts in nodes. Most languages are not designed with this in mind.
  • Godot uses several built-in data types for 2D and 3D math. Script languages do not provide this, and binding them is inefficient.
  • Godot uses threads heavily for lifting and initializing data from the net or disk. Script interpreters for common languages are not friendly to this.
  • Godot already has a memory management model for resources, most script languages provide their own, which results in duplicate effort and bugs.
  • Binding code is always messy and results in several failure points, unexpected bugs and generally low maintainability.

The result of these considerations is GDScript. The language and interpreter for GDScript ended up being smaller than the binding code itself for Lua and Squirrel, while having equal functionality. With time, having a built-in language has proven to be a huge advantage.

Example of GDScript

Some people can learn better by just taking a look at the syntax, so here’s a simple example of how GDScript looks.

# a file is a class!

# inheritance

extends BaseClass

# member variables

var a = 5
var s = "Hello"
var arr = [1, 2, 3]
var dict = {"key":"value", 2:3}

# constants

const answer = 42
const thename = "Charly"

# built-in vector types

var v2 = Vector2(1, 2)
var v3 = Vector3(1, 2, 3)

# function

func some_function(param1, param2):
    var local_var = 5

    if param1 < local_var:
        print(param1)
    elif param2 > 5:
        print(param2)
    else:
        print("fail!")

    for i in range(20):
        print(i)

    while(param2 != 0):
        param2 -= 1

    var local_var2 = param1+3
    return local_var2


# inner class

class Something:
    var a = 10

# constructor

func _init():
    print("constructed!")
    var lv = Something.new()
    print(lv.a)

If you have previous experience with statically typed languages such as C, C++, or C# but never used a dynamically typed one before, it is advised you read this tutorial: GDScript more efficiently.

Language

In the following, an overview is given to GDScript. Details, such as which methods are available to arrays or other objects, should be looked up in the linked class descriptions.

Identifiers

Any string that restricts itself to alphabetic characters (a to z and A to Z), digits (0 to 9) and _ qualifies as an identifier. Additionally, identifiers must not begin with a digit. Identifiers are case-sensitive (foo is different from FOO).

Keywords

The following is the list of keywords supported by the language. Since keywords are reserved words (tokens), they can’t be used as identifiers.

Keyword Description
if See if/else/elif.
elif See if/else/elif.
else See if/else/elif.
for See for.
do Reserved for future implementation of do...while loops.
while See while.
switch Reserved for future implementation.
case Reserved for future implementation.
break Exits the execution of the current for or while loop.
continue Immediately skips to the next iteration of the for or while loop.
pass Used where a statement is required syntactically but execution of code is undesired, e.g. in empty functions.
return Returns a value from a function.
class Defines a class.
extends Defines what class to extend with the current class. Also tests whether a variable extends a given class.
tool Executes the script in the editor.
signal Defines a signal.
func Defines a function.
static Defines a static function. Static member variables are not allowed.
const Defines a constant.
var Defines a variable.
onready Initializes a variable once the Node the script is attached to and its children are part of the scene tree.
export Saves a variable along with the resource it’s attached to and makes it visible and modifiable in the editor.
setget Defines setter and getter functions for a variable.
breakpoint Editor helper for debugger breakpoints.

Operators

The following is the list of supported operators and their precedence (TODO, change since this was made to reflect python operators)

Operator Description
x[index] Subscription, Highest Priority
x.attribute Attribute Reference
extends Instance Type Checker
~ Bitwise NOT
-x Negative
* / % Multiplication / Division / Remainder
+ - Addition / Subtraction
<< >> Bit Shifting
& Bitwise AND
^ Bitwise XOR
| Bitwise OR
< > == != >= <= Comparisons
in Content Test
! not Boolean NOT
and && Boolean AND
or || Boolean OR
= += -= *= /= %= &= |= Assignment, Lowest Priority

Literals

Literal Type
45 Base 10 integer
0x8F51 Base 16 (hex) integer
3.14, 58.1e-10 Floating point number (real)
"Hello", "Hi" Strings
"""Hello, Dude""" Multiline string
@"Node/Label" NodePath or StringName

Comments

Anything from a # to the end of the line is ignored and is considered a comment.

# This is a comment

Built-in types

Basic built-in types

A variable in GDScript can be assigned to several built-in types.

null

null is an empty data type that contains no information and can not be assigned any other value.

bool

The Boolean data type can only contain true or false.

int

The integer data type can only contain integer numbers, (both negative and positive).

float

Used to contain a floating point value (real numbers).

String

A sequence of characters in Unicode format. Strings can contain the standard C escape sequences. GDScript supports format strings aka printf functionality.

Vector built-in types

Vector2

2D vector type containing x and y fields. Can alternatively access fields as width and height for readability. Can also be accessed as array.

Rect2

2D Rectangle type containing two vectors fields: pos and size. Alternatively contains an end field which is pos+size.

Vector3

3D vector type containing x, y and z fields. This can also be accessed as an array.

Matrix32

3x2 matrix used for 2D transforms.

Plane

3D Plane type in normalized form that contains a normal vector field and a d scalar distance.

Quat

Quaternion is a datatype used for representing a 3D rotation. It’s useful for interpolating rotations.

AABB

Axis Aligned bounding box (or 3D box) contains 2 vectors fields: pos and size. Alternatively contains an end field which is pos+size. As an alias of this type, Rect3 can be used interchangeably.

Matrix3

3x3 matrix used for 3D rotation and scale. It contains 3 vector fields (x, y and z) and can also be accessed as an array of 3D vectors.

Transform

3D Transform contains a Matrix3 field basis and a Vector3 field origin.

Engine built-in types

Color

Color data type contains r, g, b, and a fields. It can also be accessed as h, s, and v for hue/saturation/value.

Image

Contains a custom format 2D image and allows direct access to the pixels.

NodePath

Compiled path to a node used mainly in the scene system. It can be easily assigned to, and from, a String.

RID

Resource ID (RID). Servers use generic RIDs to reference opaque data.

Object

Base class for anything that is not a built-in type.

InputEvent

Events from input devices are contained in very compact form in InputEvent objects. Due to the fact that they can be received in high amounts from frame to frame they are optimized as their own data type.

Container built-in types

Array

Generic sequence of arbitrary object types, including other arrays or dictionaries (see below). The array can resize dynamically. Arrays are indexed starting from index 0. Starting with Godot 2.1, indices may be negative like in Python, to count from the end.

var arr=[]
arr=[1, 2, 3]
var b = arr[1]            # this is 2
var c = arr[arr.size()-1] # this is 3
var d = arr[-1]           # same as the previous line, but shorter
arr[0] = "Hi!"            # replacing value 1 with "Hi"
arr.append(4)             # array is now ["Hi", 2, 3, 4]

GDScript arrays are allocated linearly in memory for speed. Very large arrays (more than tens of thousands of elements) may however cause memory fragmentation. If this is a concern special types of arrays are available. These only accept a single data type. They avoid memory fragmentation and also use less memory but are atomic and tend to run slower than generic arrays. They are therefore only recommended to use for very large data sets:

Dictionary

Associative container which contains values referenced by unique keys.

var d={4:5, "a key":"a value", 28:[1,2,3]}
d["Hi!"] = 0
var d = {
    22         : "Value",
    "somekey"  : 2,
    "otherkey" : [2,3,4],
    "morekey"  : "Hello"
}

Lua-style table syntax is also supported. Lua-style uses = instead of : and doesn’t use quotes to mark string keys (making for slightly less to write). Note however that like any GDScript identifier, keys written in this form cannot start with a digit.

var d = {
    test22 = "Value",
    somekey = 2,
    otherkey = [2,3,4],
    morekey = "Hello"
}

To add a key to an existing dictionary, access it like an existing key and assign to it:

var d = {} # create an empty Dictionary
d.Waiting = 14 # add String "Waiting" as a key and assign the value 14 to it
d[4] = "hello" # add integer `4` as a key and assign the String "hello" as its value
d["Godot"] = 3.01 # add String "Godot" as a key and assign the value 3.01 to it

Data

Variables

Variables can exist as class members or local to functions. They are created with the var keyword and may, optionally, be assigned a value upon initialization.

var a  # data type is null by default
var b = 5
var c = 3.8
var d = b + c  # variables are always initialized in order

Constants

Constants are similar to variables, but must be constants or constant expressions and must be assigned on initialization.

const a = 5
const b = Vector2(20, 20)
const c = 10 + 20 # constant expression
const d = Vector2(20, 30).x  # constant expression: 20
const e = [1, 2, 3, 4][0]  # constant expression: 1
const f = sin(20)  # sin() can be used in constant expressions
const g = x + 20  # invalid; this is not a constant expression!

Functions

Functions always belong to a class. The scope priority for variable look-up is: local → class member → global. The self variable is always available and is provided as an option for accessing class members, but is not always required (and should not be sent as the function’s first argument, unlike Python).

func myfunction(a, b):
    print(a)
    print(b)
    return a + b  # return is optional; without it null is returned

A function can return at any point. The default return value is null.

Referencing Functions

To call a function in a base class (i.e. one extend-ed in your current class), prepend . to the function name:

.basefunc(args)

Contrary to Python, functions are not first class objects in GDScript. This means they cannot be stored in variables, passed as an argument to another function or be returned from other functions. This is for performance reasons.

To reference a function by name at runtime, (e.g. to store it in a variable, or pass it to another function as an argument) one must use the call or funcref helpers:

# Call a function by name in one step
mynode.call("myfunction", args)

# Store a function reference
var myfunc = funcref(mynode, "myfunction")
# Call stored function reference
myfunc.call_func(args)

Remember that default functions like _init, and most notifications such as _enter_tree, _exit_tree, _process, _fixed_process, etc. are called in all base classes automatically. So there is only a need to call the function explicitly when overloading them in some way.

Static functions

A function can be declared static. When a function is static it has no access to the instance member variables or self. This is mainly useful to make libraries of helper functions:

static func sum2(a, b):
    return a + b

Statements and control flow

Statements are standard and can be assignments, function calls, control flow structures, etc (see below). ; as a statement separator is entirely optional.

if/else/elif

Simple conditions are created by using the if/else/elif syntax. Parenthesis around conditions are allowed, but not required. Given the nature of the tab-based indentation, elif can be used instead of else/if to maintain a level of indentation.

if [expression]:
    statement(s)
elif [expression]:
    statement(s)
else:
    statement(s)

Short statements can be written on the same line as the condition:

if (1 + 1 == 2): return 2 + 2
else:
    var x = 3 + 3
    return x

while

Simple loops are created by using while syntax. Loops can be broken using break or continued using continue:

while [expression]:
    statement(s)

for

To iterate through a range, such as an array or table, a for loop is used. When iterating over an array, the current array element is stored in the loop variable. When iterating over a dictionary, the index is stored in the loop variable.

for x in [5, 7, 11]:
    statement  # loop iterates 3 times with x as 5, then 7 and finally 11

var dict = {"a":0, "b":1, "c":2}
for i in dict:
    print(dict[i])  # loop provides the keys in an arbitrary order; may print 0, 1, 2, or 2, 0, 1, etc...

for i in range(3):
    statement  # similar to [0, 1, 2] but does not allocate an array

for i in range(1,3):
    statement  # similar to [1, 2] but does not allocate an array

for i in range(2,8,2):
    statement  # similar to [2, 4, 6] but does not allocate an array

for c in "Hello":
    print(c)   # iterate through all characters in a String, print every letter on new line

Classes

By default, the body of a script file is an unnamed class and it can only be referenced externally as a resource or file. Class syntax is meant to be very compact and can only contain member variables or functions. Static functions are allowed, but not static members (this is in the spirit of thread safety, since scripts can be initialized in separate threads without the user knowing). In the same way, member variables (including arrays and dictionaries) are initialized every time an instance is created.

Below is an example of a class file.

# saved as a file named myclass.gd

var a = 5

func print_value_of_a():
    print(a)

Inheritance

A class (stored as a file) can inherit from

  • A global class
  • Another class file
  • An inner class inside another class file.

Multiple inheritance is not allowed.

Inheritance uses the extends keyword:

# Inherit/extend a globally available class
extends SomeClass

# Inherit/extend a named class file
extends "somefile.gd"

# Inherit/extend an inner class in another file
extends "somefile.gd".SomeInnerClass

To check if a given instance inherits from a given class the extends keyword can be used as an operator instead:

# Cache the enemy class
const enemy_class = preload("enemy.gd")

# [...]

# use 'extends' to check inheritance
if (entity extends enemy_class):
    entity.apply_damage()

Class Constructor

The class constructor, called on class instantiation, is named _init. As mentioned earlier, the constructors of parent classes are called automatically when inheriting a class. So there is usually no need to call ._init() explicitly.

If a parent constructor takes arguments, they are passed like this:

func _init(args).(parent_args):
   pass

Inner classes

A class file can contain inner classes. Inner classes are defined using the class keyword. They are instanced using the ClassName.new() function.

# inside a class file

# An inner class in this class file
class SomeInnerClass:
    var a = 5
    func print_value_of_a():
        print(a)

# This is the constructor of the class file's main class
func _init():
    var c = SomeInnerClass.new()
    c.print_value_of_a()

Classes as resources

Classes stored as files are treated as resources. They must be loaded from disk to access them in other classes. This is done using either the load or preload functions (see below). Instancing of a loaded class resource is done by calling the new function on the class object:

# Load the class resource when calling load()
var MyClass = load("myclass.gd")

# Preload the class only once at compile time
var MyClass2 = preload("myclass.gd")

func _init():
    var a = MyClass.new()
    a.somefunction()

Exports

Class members can be exported. This means their value gets saved along with the resource (e.g. the scene) they’re attached to. They will also be available for editing in the property editor. Exporting is done by using the export keyword:

extends Button

export var number = 5  # value will be saved and visible in the property editor

An exported variable must be initialized to a constant expression or have an export hint in the form of an argument to the export keyword (see below).

One of the fundamental benefits of exporting member variables is to have them visible and editable in the editor. This way artists and game designers can modify values that later influence how the program runs. For this, a special export syntax is provided.

# If the exported value assigns a constant or constant expression,
# the type will be inferred and used in the editor

export var number = 5

# Export can take a basic data type as an argument which will be
# used in the editor

export(int) var number

# Export can also take a resource type to use as a hint

export(Texture) var character_face
export(PackedScene) var scene_file

# Integers and strings hint enumerated values

# Editor will enumerate as 0, 1 and 2
export(int, "Warrior", "Magician", "Thief") var character_class
# Editor will enumerate with string names
export(String, "Rebecca", "Mary", "Leah") var character_name

# Strings as paths

# String is a path to a file
export(String, FILE) var f
# String is a path to a directory
export(String, DIR) var f
# String is a path to a file, custom filter provided as hint
export(String, FILE, "*.txt") var f

# Using paths in the global filesystem is also possible,
# but only in tool scripts (see further below)

# String is a path to a PNG file in the global filesystem
export(String, FILE, GLOBAL, "*.png") var tool_image
# String is a path to a directory in the global filesystem
export(String, DIR, GLOBAL) var tool_dir

# The MULTILINE setting tells the editor to show a large input
# field for editing over multiple lines
export(String, MULTILINE) var text

# Limiting editor input ranges

# Allow integer values from 0 to 20
export(int, 20) var i
# Allow integer values from -10 to 20
export(int, -10, 20) var j
# Allow floats from -10 to 20, with a step of 0.2
export(float, -10, 20, 0.2) var k
# Allow values y = exp(x) where y varies betwee 100 and 1000
# while snapping to steps of 20. The editor will present a
# slider for easily editing the value.
export(float, EXP, 100, 1000, 20) var l

# Floats with easing hint

# Display a visual representation of the ease() function
# when editing
export(float, EASE) var transition_speed

# Colors

# Color given as Red-Green-Blue value
export(Color, RGB) var col  # Color is RGB
# Color given as Red-Green-Blue-Alpha value
export(Color, RGBA) var col  # Color is RGBA

# another node in the scene can be exported too

export(NodePath) var node

It must be noted that even if the script is not being run while at the editor, the exported properties are still editable (see below for “tool”).

Exporting bit flags

Integers used as bit flags can store multiple true/false (boolean) values in one property. By using the export hint int, FLAGS, they can be set from the editor:

# Individually edit the bits of an integer
export(int, FLAGS) var spell_elements = ELEMENT_WIND | ELEMENT_WATER

Restricting the flags to a certain number of named flags is also possible. The syntax is very similar to the enumeration syntax:

# Set any of the given flags from the editor
export(int, FLAGS, "Fire", "Water", "Earth", "Wind") var spell_elements = 0

In this example, Fire has value 1, Water has value 2, Earth has value 4 and Wind corresponds to value 8. Usually, constants should be defined accordingly (e.g. const ELEMENT_WIND = 8 and so on).

Using bit flags requires some understanding of bitwise operations. If in doubt, boolean variables should be exported instead.

Exporting arrays

Exporting arrays works but with an important caveat: While regular arrays are created local to every class instance, exported arrays are shared between all instances. This means that editing them in one instance will cause them to change in all other instances. Exported arrays can have initializers, but they must be constant expressions.

# Exported array, shared between all instances.
# Default value must be a constant expression.

export var a=[1,2,3]

# Typed arrays also work, only initialized empty:

export var vector3s = Vector3Array()
export var strings = StringArray()

# Regular array, created local for every instance.
# Default value can include run-time values, but can't
# be exported.

var b = [a,2,3]

Setters/getters

It is often useful to know when a class’ member variable changes for whatever reason. It may also be desired to encapsulate its access in some way.

For this, GDScript provides a setter/getter syntax using the setget keyword. It is used directly after a variable definition:

var variable = value setget setterfunc, getterfunc

Whenever the value of variable is modified by an external source (i.e. not from local usage in the class), the setter function (setterfunc above) will be called. This happens before the value is changed. The setter must decide what to do with the new value. Vice-versa, when variable is accessed, the getter function (getterfunc above) must return the desired value. Below is an example:

var myvar setget myvar_set,myvar_get

func myvar_set(newvalue):
    myvar=newvalue

func myvar_get():
    return myvar # getter must return a value

Either of the setter or getter functions can be omitted:

# Only a setter
var myvar = 5 setget myvar_set
# Only a getter (note the comma)
var myvar = 5 setget ,myvar_get

Get/Setters are especially useful when exporting variables to editor in tool scripts or plugins, for validating input.

As said local access will not trigger the setter and getter. Here is an illustration of this:

func _init():
    # Does not trigger setter/getter
    myinteger=5
    print(myinteger)

    # Does trigger setter/getter
    self.myinteger=5
    print(self.myinteger)

Tool mode

Scripts, by default, don’t run inside the editor and only the exported properties can be changed. In some cases it is desired that they do run inside the editor (as long as they don’t execute game code or manually avoid doing so). For this, the tool keyword exists and must be placed at the top of the file:

tool
extends Button

func _ready():
    print("Hello")

Memory management

If a class inherits from Reference, then instances will be freed when no longer in use. No garbage collector exists, just simple reference counting. By default, all classes that don’t define inheritance extend Reference. If this is not desired, then a class must inherit Object manually and must call instance.free(). To avoid reference cycles that can’t be freed, a weakref function is provided for creating weak references.

Signals

It is often desired to send a notification that something happened in an instance. GDScript supports creation of built-in Godot signals. Declaring a signal in GDScript is easy using the signal keyword.

# No arguments
signal your_signal_name
# With arguments
signal your_signal_name_with_args(a,b)

These signals, just like regular signals, can be connected in the editor or from code. Just take the instance of a class where the signal was declared and connect it to the method of another instance:

func _callback_no_args():
    print("Got callback!")

func _callback_args(a,b):
    print("Got callback with args! a: ",a," and b: ",b)

func _at_some_func():
    instance.connect("your_signal_name",self,"_callback_no_args")
    instance.connect("your_signal_name_with_args",self,"_callback_args")

It is also possible to bind arguments to a signal that lacks them with your custom values:

func _at_some_func():
    instance.connect("your_signal_name",self,"_callback_args",[22,"hello"])

This is very useful when a signal from many objects is connected to a single callback and the sender must be identified:

func _button_pressed(which):
    print("Button was pressed: ",which.get_name())

func _ready():
    for b in get_node("buttons").get_children():
        b.connect("pressed",self,"_button_pressed",[b])

Finally, emitting a custom signal is done by using the Object.emit_signal method:

func _at_some_func():
    emit_signal("your_signal_name")
    emit_signal("your_signal_name_with_args",55,128)
    someinstance.emit_signal("somesignal")

Coroutines

GDScript offers support for coroutines via the yield built-in function. Calling yield() will immediately return from the current function, with the current frozen state of the same function as the return value. Calling resume on this resulting object will continue execution and return whatever the function returns. Once resumed the state object becomes invalid. Here is an example:

func myfunc():

   print("hello")
   yield()
   print("world")

func _ready():

    var y = myfunc()
    # Function state saved in 'y'
    print("my dear")
    y.resume()
    # 'y' resumed and is now an invalid state

Will print:

hello
my dear
world

It is also possible to pass values between yield() and resume(), for example:

func myfunc():

   print("hello")
   print( yield() )
   return "cheers!"

func _ready():

    var y = myfunc()
    # Function state saved in 'y'
    print( y.resume("world") )
    # 'y' resumed and is now an invalid state

Will print:

hello
world
cheers!

Coroutines & signals

The real strength of using yield is when combined with signals. yield can accept two parameters, an object and a signal. When the signal is received, execution will recommence. Here are some examples:

# Resume execution the next frame
yield( get_tree(), "idle_frame" )

# Resume execution when animation is done playing:
yield( get_node("AnimationPlayer"), "finished" )

Onready keyword

When using nodes, it’s very common to desire to keep references to parts of the scene in a variable. As scenes are only warranted to be configured when entering the active scene tree, the sub-nodes can only be obtained when a call to Node._ready() is made.

var mylabel

func _ready():
    mylabel = get_node("MyLabel")

This can get a little cumbersome, specially when nodes and external references pile up. For this, GDScript has the onready keyword, that defers initialization of a member variable until _ready is called. It can replace the above code with a single line:

onready var mylabel = get_node("MyLabel")