Godot Behavior Tree & Navigation Tutorial (P3 - Enemy path finding)

Introduction

In this tutorial, we will learn how to implement enemy pathfinding using behavior trees in the Godot engine. This guide will walk you through creating a new enemy node and writing a script to enable the enemy to navigate towards the player. By the end, you'll have a functional enemy AI that can follow the player in a game environment.

Step 1: Adding Enemy Asset

• Download Kenney's top-down shooter asset from Kenney's website.
• Import the enemy sprite into your Godot project.
• Ensure the asset is correctly placed in your scene to be utilized in the next steps.

Step 2: Create a New Enemy Node

• In the Godot editor, create a new scene for the enemy.
• In the scene, add a KinematicBody2D node and name it "Enemy."
• Add a Sprite node as a child of the Enemy node to display the enemy asset.
• Optionally, add a CollisionShape2D to handle collisions with the player and the environment.

Step 3: Writing the Enemy Script

• Create a new script for the Enemy node by right-clicking on the Enemy node and selecting "Attach Script."
• In the script, you will define the pathfinding logic. Start with the following code:

extends KinematicBody2D

var speed = 100
onready var nav_path = []
var target_position

func _process(delta):
    if nav_path.size() > 0:
        move_along_path(delta)

func move_along_path(delta):
    var next_node = nav_path[0]
    var direction = (next_node - global_position).normalized()
    global_position += direction * speed * delta
    
    if global_position.distance_to(next_node) < 10:
        nav_path.remove(0)

• This code initializes movement towards the next node in the path.

Step 4: Fixing Root Node Error

• Ensure that the root node is correctly set to avoid errors when running the game.
• Check the script's logic and ensure all nodes are properly referenced.

Step 5: Testing the Enemy Pathfinding

• Run the game to test if the enemy can navigate towards the player.
• Observe the behavior of the enemy as it attempts to follow the player’s position.

Step 6: Implementing Enemy Movement Script

• Refine the enemy movement script by adding logic for smoother movement.
• Integrate interpolation to ensure the enemy moves fluidly between points. Here’s an example:

func move_along_path(delta):
    var next_node = nav_path[0]
    var direction = (next_node - global_position).normalized()
    global_position = global_position.linear_interpolate(next_node, speed * delta)
    
    if global_position.distance_to(next_node) < 10:
        nav_path.remove(0)

Step 7: Handling Movement Past Path Nodes

• Modify the script to handle situations when the enemy overshoots the path nodes.
• Update the condition to ensure it adjusts the enemy's final position correctly:

if global_position.distance_to(next_node) < 10 and nav_path.size() > 1:
    self.global_position = nav_path[1]

Step 8: Final Testing of Movement

• Test the game again to ensure that the enemy behaves correctly as it follows the path to the player.
• Make adjustments to speed, pathfinding logic, or collision handling as necessary to improve performance.

Conclusion

You have successfully created an enemy AI that can navigate towards the player using behavior trees in Godot. Key points included setting up the enemy node, writing the movement script, and refining the pathfinding logic. For further enhancements, consider adding more complex behaviors or integrating additional enemy types. Happy game developing!