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
Multi-line comments can be created using “”” (three quotes in a row) at the beginning and end of a block of text.
""" Everything on these
lines is considered
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
.
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.
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.
NodePath¶
Compiled path to a node used mainly in the scene system. It can be easily assigned to, and from, a String.
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:
- ByteArray: An array of bytes (integers from 0 to 255).
- IntArray: An array of integers.
- FloatArray: An array of floats.
- StringArray: An array of strings.
- Vector2Array: An array of Vector2 objects.
- Vector3Array: An array of Vector3 objects.
- ColorArray: An array of Color objects.
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
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
# 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")