PhysicsBody3D in Godot – Complete Guide

Welcome to an intriguing journey into the world of physics in game development! Physics are the backbone of interactivity and realism in games, and Godot 4 provides a robust framework for simulating physics with its PhysicsBody3D class. This tutorial aims to unravel the complexities of PhysicsBody3D, helping you garner a functional understanding that can be applied to create compelling and realistic game experiences. Whether you’re building your first game or looking to enhance your expertise, this guide is tailored to breathe life into your 3D objects by cloaking them with the laws of physics.

What is PhysicsBody3D?

The PhysicsBody3D class in Godot 4 acts as an abstract base class for three-dimensional game objects that are influenced by physics. It’s the cornerstone of all physics-related interactions and a parent to a variety of specialized physics bodies such as CharacterBody3D, RigidBody3D, and StaticBody3D. Understanding PhysicsBody3D is essential because it defines the behaviors that are shared across all the physics-driven entities in your game.

What is it for?

Using PhysicsBody3D, developers can create objects that can move, interact, and respond to collisions based on real-world physics laws—with minimal coding. Think of it as giving your game assets a real sense of mass, gravity, and inertia. It can simulate everything from the simple dropping of an apple to the complex movement of a character navigating a dynamic environment.

Why Should I Learn It?

Delving into the PhysicsBody3D class elevates your ability to manifest rich, interactive environments. Games today are expected to deliver highly engaging and realistic functionalities. Learning to manipulate this component effectively can greatly differentiate your game from the masses – by rendering interactions that feel intuitive to players. Additionally, solid knowledge of physics in Godot is transferable to other game engines and broadens your skillset as a game developer.

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Creating a StaticBody3D

Static bodies are essential for objects that you want to include in your game world that will not move. They are perfect for elements like floors, walls, or obstacles.

var static_body = StaticBody3D.new()
static_body.name = "Floor"
var collision_shape = CollisionShape3D.new()
collision_shape.shape = BoxShape.new()
collision_shape.shape.extents = Vector3(10, 1, 10)
static_body.add_child(collision_shape)
add_child(static_body)

In the above snippet, we create a new instance of StaticBody3D and assign it a shape using CollisionShape3D. We set the shape to be a box of certain extents, to act as our floor in the game world.

Working with a RigidBody3D

Rigid bodies are objects which simulate physics like gravity and collisions without our direct interference. A bouncing ball would be a typical use case.

var rigid_body = RigidBody3D.new()
rigid_body.name = "BouncingBall"
var collision_shape = CollisionShape3D.new()
collision_shape.shape = SphereShape.new()
collision_shape.shape.radius = 1
rigid_body.add_child(collision_shape)
add_child(rigid_body)

Here, we construct a simple sphere and assign it to the new RigidBody3D, which would automatically react to gravity and bounce around based on the physics properties defined within Godot 4.

Setting up a KinematicBody3D

A kinematic body is a type of body which is meant to be controlled by the user or AI, with physics applied only when you decide.

var kinematic_body = KinematicBody3D.new()
kinematic_body.name = "Player"
var collision_shape = CollisionShape3D.new()
collision_shape.shape = CapsuleShape.new()
collision_shape.shape.radius = 1
collision_shape.shape.height = 2
kinematic_body.add_child(collision_shape)
add_child(kinematic_body)

With the KinematicBody3D defined, we can move it using Godot’s move_and_slide or move_and_collide methods, offering a mixture of manual control and physics-based collision response.

Implementing Gravity

Gravity is a pivotal aspect of realism in a game. Here’s how you can implement gravity on a rigid body to simulate the natural drop.

func _ready():
    var rigid_body = $RigidBody3D
    rigid_body.gravity_scale = 9.8  # Standard gravity

By adjusting the gravity scale, you can make the object respond to gravity instantly, ensuring that the object will ‘fall’ towards the ground when spawned into the game.

Adding Movement to KinematicBody3D

Movement of kinematic bodies can be made responsive and realistic with Godot’s built-in methods.

func _physics_process(delta):
    var velocity = Vector3()  # Start with zero velocity
    if Input.is_action_pressed("ui_right"):
        velocity.x += 1
    if Input.is_action_pressed("ui_left"):
        velocity.x -= 1
    velocity = velocity.normalized() * speed
    velocity = move_and_slide(velocity)

Here we define movement based on player input, normalizing the velocity to ensure consistent movement speed regardless of framerate, and applying it using the move_and_slide method.

Remember, mastering physics in Godot is not just about understanding the individual components but also learning how they all come together to create interactive and engaging gameplay. Stay tuned for further examples in the next part of the series.Continuing with our exploration into Godot 4’s PhysicsBody3D, let’s delve a bit deeper into how we can leverage this system to create a more engaging and dynamic game environment. We’ll explore applying forces, detecting collisions, linking scripts, and using signals for enhanced physics interactions.

Applying Forces to a RigidBody3D
Manipulating the motion of objects through applied forces and impulses is a core aspect of physics in games. Here’s how you can add a force to a ribid body:

func _physics_process(delta):
    var rigid_body = $RigidBody3D
    var force_vector = Vector3(100, 0, 0)  # Force to the right
    rigid_body.apply_central_impulse(force_vector)

The apply_central_impulse function instantly changes the velocity of the object. It’s similar to giving the object a quick, strong shove in the direction of the provided vector.

Detecting Collisions with RigidBody3D
Collision detection is vital for gameplay logic. Here’s an example of handling collisions with a RigidBody3D in Godot:

func _integrate_forces(state):
    var contacts = state.get_contact_count()
    for i in range(contacts):
        var collider = state.get_contact_collider(i)
        if collider.is_in_group("Hazard"):
            print("Collided with a hazard!")

The _integrate_forces physics callback allows you to access the PhysicsDirectBodyState object, where you can get the number of contacts and information about what the body has collided with.

Linking Scripts to Physics Bodies
Scripts can be attached to physics bodies to define custom behavior and interaction logic. Here’s a brief example of how to link a script to a StaticBody3D:

var static_body = StaticBody3D.new()
static_body.name = "Platform"
static_body.set_script(preload("res://PlatformScript.gd"))
add_child(static_body)

By using the set_script method, we dynamically attach a preloaded script, allowing the platform to have its own set of properties and behaviors, such as being a moving platform or having special effects upon contact.

Using Signals with KinematicBody3D
Godot’s signal system allows KinematicBody3D objects to communicate with other nodes or scripts upon certain events, such as entering a certain area:

func _ready():
    var area = $Area3D
    area.connect("body_entered", self, "_on_Body_Entered")

func _on_Body_Entered(body):
    if body.name == "Player":
        print("Player has entered the area")

We connect the “body_entered” signal from an Area3D node to a custom function in our script, allowing us to respond whenever the player enters this area.

Rotation and Torque in RigidBody3D
To make a RigidBody3D rotate, you can apply torque—a rotational force. Here’s a way to make a RigidBody3D spin along the Y-axis:

func _ready():
    var rigid_body = $RigidBody3D
    rigid_body.apply_torque_impulse(Vector3(0, 10, 0))

The apply_torque_impulse method applies a torque impulse to the body, initiating a spin that will react naturally according to the game’s physics settings.

In the above examples, we touched on several aspects of how you can program physics behaviors within Godot 4. As you get more comfortable with these functions and processes, you can start making more sophisticated and responsive game physics. Always bear in mind that interactivity and realism in your games hinge on the delicate balance of these physics-based systems. Make sure to experiment and find the right feel for your particular game.Incorporating advanced physics interactions into your game can significantly enhance the player’s experience. Let’s dive into some more sophisticated examples of working with Godot 4’s PhysicsBody3D to achieve effects such as buoyancy, forces at points, raycasting, and more.

Buoyancy with RigidBody3D
Simulating buoyancy allows objects to float in water or other fluids. To achieve this effect, you could adjust the mass and apply forces based on the object’s submersion depth.

func _physics_process(delta):
    var water_level = 5.0  # Example water level on the Y-axis
    var body_position = $RigidBody3D.global_transform.origin
    if body_position.y < water_level:
        var submersion = water_level - body_position.y
        var buoyancy_force = Vector3(0, submersion * 100, 0)  # Upward force proportional to submersion
        $RigidBody3D.apply_central_impulse(buoyancy_force)

This ensures that if the RigidBody3D goes below a certain water level, an upward force is applied to simulate buoyancy, keeping the object afloat.

Applying Forces at Points
Sometimes, you might want to apply a force to a specific point on a rigid body, which could cause it to move and rotate in a more realistic manner.

func _physics_process(delta):
    var rigid_body = $RigidBody3D
    var force_vector = Vector3(100, 0, 0)  # Force to the right
    var application_point = Vector3(0, 1, 0)  # Apply the force at a point above the center of mass

    rigid_body.apply_impulse(application_point, force_vector)

By applying an impulse at a point other than the center of mass, a RigidBody3D can experience both translation and rotation, adding to the realism.

Raycasting to Detect Obstacles
Raycasting is a method used to detect objects in a line from a starting point to an end point. It’s useful for line of sight, shooting mechanics, or scanning for objects within a path.

func _physics_process(delta):
    var space_state = get_world_3d().direct_space_state
    var ray_origin = $Camera.global_transform.origin
    var ray_end = ray_origin + ($Camera.global_transform.basis.z * -100)

    var result = space_state.intersect_ray(ray_origin, ray_end)
    if result:
        print("Hit: ", result.collider.name)

Here, a ray is cast from the camera’s position forward along the negative Z-axis. If the ray hits an object, it prints out the name of the collider.

Detecting the Ground with Raycasting
For character controllers, particularly with KinematicBody3D, knowing if the character is on the ground is essential for implementing jump mechanics and more. Raycasting can be used to detect the ground:

func _physics_process(delta):
    var is_on_ground = false
    var ray_length = 5.0
    var space_state = get_world_3d().direct_space_state
    var from = global_transform.origin
    var to = from + Vector3.DOWN * ray_length

    var result = space_state.intersect_ray(from, to)
    if result and result.collider is StaticBody3D:
        is_on_ground = true

The intersect_ray function checks a line directly downward from the character’s position. If there’s a StaticBody3D collider within the ray’s length, it’s considered that the character is on the ground.

Simulating Wind with Area3D
To simulate environmental forces such as wind, you can use Area3D to create zones where physics is affected differently.

func _ready():
    var wind_zone = $Area3D
    wind_zone.space_override_mode = Area3D.SPACE_OVERRIDE_COMBINE
    wind_zone.gravity_vec = Vector3(5, 0, 0)  # Force to the right simulating wind
    wind_zone.gravity = 9.8
    wind_zone.gravity_point = false

This code snippet creates a wind effect in an Area3D node by overriding the default gravity vector. Objects that enter this area will be subjected to additional forces, simulating wind pushing them to the right.

By combining these techniques, you can start creating rich, physically interactive worlds that resonate with the players’ expectations for a responsive and engaging game environment. These examples only scratch the surface of what’s possible with Godot 4’s PhysicsBody3D class. As you experiment with these tools, you’ll unlock the full potential of Godot’s 3D physics system for your projects.

Where to Go Next?

Mastering physics in Godot 4 is just the beginning of your game development journey. To take your skills to the next level, consider our Godot Game Development Mini-Degree. This comprehensive series of courses guides you through creating cross-platform games using the latest version of Godot. You’ll learn about asset management, dive into GDScript, control game flow, and build various game mechanics, all while working on real projects that can become part of your portfolio.

Whether you’re a beginner or an experienced developer, our curated curriculum offers step-by-step instructions and allows you to leap into advanced lessons that align with your learning goals. Our project-based approach means you get practical experience right from the start, and with flexible online resources, you can study at your own pace. Over a million others have chosen Zenva for their educational journey into game development and programming.

If you’re looking for an even more extensive learning path, visit our array of Godot courses. From crafting beautiful 2D games to pushing the boundaries of 3D spaces, our library contains everything you need to continue growing your skills and fueling your passion for game development.

At Zenva, we’re proud to help you advance from the basics to professional levels, so whenever you’re ready to expand your horizons in the world of game creation, we’re here to support your journey. Keep coding, keep creating, and turn your game development dreams into reality.

Conclusion

Embarking on the adventure of game development with Godot 4 opens up a world of possibilities. As we’ve seen through the exploration of the PhysicsBody3D class and its derivatives, you have a powerful suite of tools at your fingertips, ready to breathe life into your gaming visions. The versatile nature of Godot’s physics system, combined with your creativity, will undoubtedly lead to unique and immersive game experiences that stand out.

We at Zenva believe in empowering creators like you with the knowledge and resources to transform your ideas into interactive realities. Our Godot Game Development Mini-Degree is designed to guide you every step of the way. So why wait? Join the ranks of successful game developers and start crafting your masterpiece today. Let’s shape the future of gaming together with Godot and Zenva.

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