GDScript Programming Basics

# CHAPTER 5

GDScript Programming Basics #

1. Introduction #

2. Learning Objectives #

• Attach a script to a Node in the Godot Editor.

• Understand GDScript syntax (indentation and keywords).

• Declare Variables and write custom Functions.

• Use conditional logic (if, elif, else).

• Connect and emit Signals (Godot's event system).

3. Attaching a Script #

1. 1. Select a Node in the Scene Panel (e.g., Player).

1. 2. Click the Attach Script button (the small scroll icon with a green '+').

1. 3. Click Create. Godot switches to the "Script" workspace, and you see a blank text file ending in .gd.

4. GDScript Syntax (The Rules of the Language) #

• Extends: The first line is usually extends Node2D. This tells the script, "I am attached to a Node2D, give me access to all of its abilities."

• Indentation is Mandatory: GDScript does not use curly brackets {}. It uses tabs (indentations) to group code. If your indentation is wrong, the code will crash.

• Comments: Any line starting with a # is ignored by the computer. Use it to write notes to yourself.

5. Variables and Functions #

• Variables store data (like memory boxes). Use the var keyword.

• Functions are blocks of code that perform an action. Use the func keyword.

• _ready(): Runs exactly once when the game starts.

• _process(delta): Runs every single frame (e.g., 60 times a second).

extends Node2D

# 1. Variables
var player_name = "Hero"  # A string (text)
var health = 100          # An integer (whole number)
var speed = 2.5           # A float (decimal number)

# 2. Built-in Function (Runs at start)
func _ready():
    print("Welcome to the game, " + player_name)
    take_damage(20) # Calling our custom function

# 3. Custom Function
func take_damage(amount):
    health = health - amount
    print("Health is now: ", health)

6. Logic and Conditions (If Statements) #

func check_death():
    if health <= 0:
        print("Game Over!")
    elif health < 20:
        print("Warning: Low Health!")
    else:
        print("Player is fine.")

7. Signals (The Communication System) #

• *Visual Connection:* You can select a Button, go to the "Node" dock (next to the Inspector), double-click the pressed() signal, and attach it to your script visually.

8. Visual Learning: The Signal Flow #

[ Node: StartButton ] 
  |
  +-- (Player clicks button)
  |
  +-- Emits Signal: `pressed`
          |
          v
(Wire connects signal to Level script)
          |
          v
[ Node: LevelManager (Script) ]
  func _on_StartButton_pressed():
      print("Starting Level 1!")
      load_level()

9. Best Practices #

• Use Static Typing (Optional but great): In GDScript, you can force a variable to *only* hold a specific type of data by using a colon. var health: int = 100. This prevents bugs (like accidentally trying to store the word "Apple" inside a health variable) and makes the code run slightly faster.

10. Common Mistakes #

• Indentation Errors: A beginner writes an if statement, but the next line is flush against the left wall instead of indented by one tab. The engine throws an "Expected indented block" error. *Always press Tab after a colon :!*

11. Mini Project: The Health Calculator #

1. 1. Create a Node2D scene. Attach a script to it.

1. 2. In the script, delete everything and write the following:

extends Node2D

var hp: int = 100

func _ready():
    print("Start Game. HP: ", hp)
    take_hit(40)
    take_hit(70)

func take_hit(damage: int):
    hp -= damage
    print("Took ", damage, " damage. Current HP: ", hp)
    
    if hp <= 0:
        print("Player Died!")

1. 3. Press Play. Look at the "Output" console window at the bottom of the screen. You should see the math happen and the "Player Died!" message print.

12. Practice Exercises #

1. 1. What keyword is used to declare a variable in GDScript?

1. 2. Explain the difference between the _ready() function and the _process(delta) function.

13. MCQs with Answers #

14. Interview Questions #

• Q: GDScript is often compared to Python. What are the key syntactic similarities, and what makes GDScript uniquely suited for the Godot Engine?

• Q: Explain the Observer Pattern in the context of Godot. How do Signals solve the problem of tightly coupled code between different nodes?

• Q: Walk me through what extends CharacterBody2D means at the top of a script. What is inheritance in Object-Oriented Programming?

15. FAQs #

16. Summary #

17. Next Chapter Recommendation #