【Godot】Flexible Object Detection with Groups

Overview

As games become more complex, situations increase where you want to handle specific types of objects collectively - "send the same command to all enemies," "check if the player's attack hit an 'items' group object."

Godot's Groups feature elegantly addresses these needs. Groups are a very convenient mechanism for tagging nodes with labels like "enemy," "item," "destructible object," then using those tags to find or batch-operate on nodes.

This article explains the basic usage of Godot's group feature and how it enables flexible object management.

What are Groups?

Groups are a tagging system for virtually classifying nodes into collections, independent of scene tree hierarchy. A single node can belong to multiple groups, and groups are shared across the entire project.

Key Benefits of Groups:

Flexible Classification: Classify objects freely regardless of node type (CharacterBody2D, Area2D, etc.) or parent-child relationships
Batch Operations: Easily get all nodes in a specific group and call the same method on them
Loose Coupling: Nodes can interact indirectly through groups without directly knowing each other. This improves code clarity

How to Set Up Groups

There are two ways to add nodes to groups: through the editor and through code.

1. Setting Up in the Editor

The easiest and most common method.

Select the node you want to add to a group in the scene tree
Open the "Node" tab next to the Inspector
Select the "Groups" tab
Enter a group name (e.g., enemies) in the text box and press "Add"

The selected node is now a member of the enemies group.

2. Setting Up in Code

Used when you want to add dynamically generated nodes to groups.

func _ready():
    # Add this node to the "bullets" group
    add_to_group("bullets")

# Can also remove from group
func _on_hit_target():
    remove_from_group("bullets")

Group Usage Examples

The true value of groups lies in how you use them from scripts.

Example 1: Get Nodes in a Specific Group

The SceneTree object (obtained via get_tree()) has convenient methods for manipulating groups.

# Get all nodes in the "enemies" group in the scene
func _ready():
    var all_enemies = get_tree().get_nodes_in_group("enemies")
    for enemy in all_enemies:
        print(enemy.name)

Example 2: Broadcast Commands to All Nodes in a Group

Using SceneTree's call_group() method, you can call a specific function on all nodes in a particular group at once. For example, pausing all enemy characters when a boss appears.

# Boss.gd
func _on_boss_appeared():
    # Call the "pause_movement" method on all nodes in "enemies" group
    get_tree().call_group("enemies", "pause_movement")

# Enemy.gd
func pause_movement():
    # Processing to stop movement
    set_physics_process(false)

Example 3: Use in Collision Detection

Combined with Area2D's body_entered signal, you can easily check if a collided object belongs to a specific group.

# Player.gd
func _on_body_entered(body):
    # Check if collided object is in "enemies" group
    if body.is_in_group("enemies"):
        take_damage()

    # Check if collided object is in "items" group
    if body.is_in_group("items"):
        body.collect() # Call item's collection process

This eliminates the need for inflexible code like if body.name == "Slime" or body.name == "Goblin" ....

Summary

The group feature is a powerful weapon for writing organized, extensible code in Godot. The simple concept of tagging objects and using those tags to find and operate on them has a very wide range of applications.

Classify by roles like enemies and items
Gather objects you want to batch operate on
Identify the other party's type in collision detection

When you encounter these situations, consider using the group feature. Your project will become cleaner and easier to manage.

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