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https://github.com/adambard/learnxinyminutes-docs.git
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323 lines
8.8 KiB
Markdown
323 lines
8.8 KiB
Markdown
---
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language: GDScript
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contributors:
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- ["Wichamir", "https://github.com/Wichamir/"]
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filename: learngdscript.gd
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---
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GDScript is a dynamically typed scripting language made specifically for
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free and open source game engine Godot. GDScript's syntax is similar to
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Python's. Its main advantages are ease of use and tight integration with
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the engine. It's a perfect fit for game development.
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## Basics
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```nim
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# Single-line comments are written using hash symbol.
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"""
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Multi-line
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comments
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are
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written
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using
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docstrings.
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"""
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# Script file is a class in itself and you can optionally define a name for it.
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class_name MyClass
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# Inheritance
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extends Node2D
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# Member variables
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var x = 8 # int
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var y = 1.2 # float
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var b = true # bool
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var s = "Hello World!" # String
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var a = [1, false, "brown fox"] # Array - similar to list in Python,
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# it can hold different types
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# of variables at once.
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var d = {
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"key" : "value",
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42 : true
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} # Dictionary holds key-value pairs.
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var p_arr = PoolStringArray(["Hi", "there", "!"]) # Pool arrays can
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# only hold a certain type.
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# Built-in vector types:
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var v2 = Vector2(1, 2)
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var v3 = Vector3(1, 2, 3)
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# Constants
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const ANSWER_TO_EVERYTHING = 42
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const BREAKFAST = "Spam and eggs!"
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# Enums
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enum { ZERO, ONE , TWO, THREE }
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enum NamedEnum { ONE = 1, TWO, THREE }
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# Exported variables are visible in the inspector.
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export(int) var age
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export(float) var height
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export var person_name = "Bob" # Export type hints are unnecessary
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# if you set a default value.
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# Functions
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func foo():
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pass # pass keyword is a placeholder for future code
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func add(first, second):
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return first + second
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# Printing values
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func printing():
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print("GDScript ", "is ", " awesome.")
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prints("These", "words", "are", "divided", "by", "spaces.")
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printt("These", "words", "are", "divided", "by", "tabs.")
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printraw("This gets printed to system console.")
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# Math
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func doing_math():
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var first = 8
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var second = 4
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print(first + second) # 12
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print(first - second) # 4
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print(first * second) # 32
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print(first / second) # 2
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print(first % second) # 0
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# There are also +=, -=, *=, /=, %= etc.,
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# however no ++ or -- operators.
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print(pow(first, 2)) # 64
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print(sqrt(second)) # 2
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printt(PI, TAU, INF, NAN) # built-in constants
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# Control flow
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func control_flow():
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x = 8
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y = 2 # y was originally a float,
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# but we can change its type to int
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# using the power of dynamic typing!
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if x < y:
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print("x is smaller than y")
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elif x > y:
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print("x is bigger than y")
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else:
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print("x and y are equal")
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var a = true
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var b = false
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var c = false
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if a and b or not c: # alternatively you can use &&, || and !
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print("This is true!")
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for i in range(20): # GDScript's range is similar to Python's
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print(i) # so this will print numbers from 0 to 19
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for i in ["two", 3, 1.0]: # iterating over an array
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print(i)
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while x > y:
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printt(x, y)
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y += 1
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x = 2
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y = 10
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while x < y:
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x += 1
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if x == 6:
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continue # 6 won't get printed because of continue statement
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prints("x is equal to:", x)
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if x == 7:
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break # loop will break on 7, so 8, 9 and 10 won't get printed
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match x:
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1:
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print("Match is similar to switch.")
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2:
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print("However you don't need to put cases before each value.")
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3:
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print("Furthermore each case breaks on default.")
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break # ERROR! Break statement is unnecessary!
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4:
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print("If you need fallthrough use continue.")
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continue
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_:
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print("Underscore is a default case.")
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# ternary operator (one line if-else statement)
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prints("x is", "positive" if x >= 0 else "negative")
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# Casting
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func casting_examples():
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var i = 42
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var f = float(42) # cast using variables constructor
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var b = i as bool # or using "as" keyword
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# Override functions
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# By a convention built-in overridable functions start with an underscore,
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# but in practice you can override virtually any function.
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# _init is called when object gets initialized
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# This is the object's constructor.
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func _init():
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# Initialize object's internal stuff here.
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pass
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# _ready gets called when script's node and
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# its children have entered the scene tree.
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func _ready():
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pass
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# _process gets called on every frame.
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func _process(delta):
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# The delta argument passed to this function is a number of seconds,
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# which passed between the last frame and the current one.
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print("Delta time equals: ", delta)
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# _physics_process gets called on every physics frame.
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# That means delta should be constant.
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func _physics_process(delta):
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# Simple movement using vector addition and multiplication.
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var direction = Vector2(1, 0) # or Vector2.RIGHT
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var speed = 100.0
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self.global_position += direction * speed * delta
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# self refers to current class instance
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# When overriding you can call parent's function using the dot operator
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# like here:
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func get_children():
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# Do some additional things here.
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var r = .get_children() # call parent's implementation
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return r
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# Inner class
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class InnerClass:
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extends Object
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func hello():
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print("Hello from inner class!")
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func use_inner_class():
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var ic = InnerClass.new()
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ic.hello()
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ic.free() # use free for memory cleanup
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```
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## Accessing other nodes in the scene tree
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```nim
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extends Node2D
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var sprite # This variable will hold the reference.
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# You can get references to other nodes in _ready.
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func _ready() -> void:
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# NodePath is useful for accessing nodes.
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# Create NodePath by passing String to its constructor:
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var path1 = NodePath("path/to/something")
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# Or by using NodePath literal:
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var path2 = @"path/to/something"
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# NodePath examples:
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var path3 = @"Sprite" # relative path, immediate child of the current node
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var path4 = @"Timers/Firerate" # relative path, child of the child
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var path5 = @".." # current node's parent
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var path6 = @"../Enemy" # current node's sibling
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var path7 = @"/root" # absolute path, equivalent to get_tree().get_root()
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var path8 = @"/root/Main/Player/Sprite" # absolute path to Player's Sprite
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var path9 = @"Timers/Firerate:wait_time" # accessing properties
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var path10 = @"Player:position:x" # accessing subproperties
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# Finally, to get a reference use one of these:
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sprite = get_node(@"Sprite") as Sprite # always cast to the type you expect
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sprite = get_node("Sprite") as Sprite # here String gets
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# implicitly casted to NodePath
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sprite = get_node(path3) as Sprite
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sprite = get_node_or_null("Sprite") as Sprite
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sprite = $Sprite as Sprite
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func _process(delta):
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# Now we can reuse the reference in other places.
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prints("Sprite has global_position of", sprite.global_position)
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# Use onready keyword to assign a value to
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# a variable just before _ready executes.
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# This is a commonly used syntax sugar.
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onready var tween = $Tween as Tween
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# You can export NodePath, so you can assign it within the inspector.
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export var nodepath = @""
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onready var reference = get_node(nodepath) as Node
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```
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## Signals
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Signal system is Godot's implementation of the observer programming
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pattern. Here's an example:
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```nim
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class_name Player extends Node2D
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var hp = 10
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signal died() # define signal
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signal hurt(hp_old, hp_new) # signals can take arguments
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func apply_damage(dmg):
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var hp_old = hp
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hp -= dmg
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emit_signal("hurt", hp_old, hp) # emit signal and pass arguments
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if hp <= 0:
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emit_signal("died")
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func _ready():
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# connect signal "died" to function "_on_death" defined in self
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self.connect("died", self, "_on_death")
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func _on_death():
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self.queue_free() # destroy Player on death
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```
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## Type hints
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GDScript can optionally use static typing.
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```nim
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extends Node
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var x: int # define typed variable
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var y: float = 4.2
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var z := 1.0 # infer type based on default value using := operator
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onready var node_ref_typed := $Child as Node
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export var speed := 50.0
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const CONSTANT := "Typed constant."
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func _ready() -> void:
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# function returns nothing
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x = "string" # ERROR! Type can't be changed!
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return
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func join(arg1: String, arg2: String) -> String:
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# function takes two Strings and returns a String
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return arg1 + arg2
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func get_child_at(index: int) -> Node:
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# function takes an int and returns a Node
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return get_children()[index]
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signal example(arg: int) # ERROR! Signals can't take typed arguments!
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```
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## Further Reading
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* [Godot's Website](https://godotengine.org/)
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* [Godot Docs](https://docs.godotengine.org/en/stable/)
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* [Getting started with GDScript](https://docs.godotengine.org/en/stable/getting_started/scripting/gdscript/index.html)
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* [NodePath](https://docs.godotengine.org/en/stable/classes/class_nodepath.html)
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* [Signals](https://docs.godotengine.org/en/stable/getting_started/step_by_step/signals.html)
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* [GDQuest](https://www.gdquest.com/)
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* [GDScript.com](https://gdscript.com/)
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