XRPositionalTracker in Godot – Complete Guide

Welcome to a deep dive into the world of XR positional tracking in Godot 4. In this tutorial, we will unravel the capabilities of the XRPositionalTracker class. Understanding how to utilize this system can transform your virtual reality (VR) or augmented reality (AR) creations, providing immersive and interactive user experiences. Whether you’re just beginning with XR development or looking to refine your skills, this series promises to equip you with the knowledge to implement advanced tracking features into your projects.

What is XRPositionalTracker?

The XRPositionalTracker class in Godot 4 is a fundamental component for tracking devices within an XR environment. It represents elements like controllers or anchors that are physically tracked in space. What sets this class apart is that it doesn’t account for head-mounted displays (HMDs), as those are internally managed by the game engine.

What is it for?

Suppose you are developing an XR application. In that scenario, the XRPositionalTracker allows you to interact with and retrieve data from various tracked devices. This is crucial for implementing motion controls, object interaction, and precise emulation of player movements within the virtual world.

Why should I learn it?

Understanding the XRPositionalTracker class and its functionalities is essential for any aspiring XR developer. It serves as a foundation for creating responsive and intuitive XR applications, giving players a greater sense of presence and engagement. By mastering XR positional tracking, you can:

  • Enhance player immersion with accurate tracking of movement and gestures.
  • Develop sophisticated interaction systems that elevate gameplay experiences.
  • Adapt to a variety of XR hardware and ecosystem nuances effectively.

Now, let’s jump into the tutorial and start bringing the digital to life.

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Getting Started with the XRPositionalTracker

To get started with the XRPositionalTracker, we need to first initialize our XR interface. This example assumes you have a running XR project and will guide you through setting up the tracker.

var xr_interface = ARVRServer.find_interface("Some_XR_Interface")
if xr_interface and xr_interface.initialize():
    print("XR Interface initialized successfully")
else:
    print("Failed to initialize XR Interface")

Once the XR Interface is initialized, we can start querying the position of our devices.

var tracker = XRPositionalTracker.new()
if tracker:
    print("Tracker has been created.")

Tracking Controller Positions

With our tracker set up, we can now query the position of our controllers. We will do this within the _process loop for real-time updates.

func _process(delta):
    var left_hand_tracker = XRPositionalTracker.new()
    left_hand_tracker.set_type(ARVRServer.TRACKER_CONTROLLER)
    left_hand_tracker.set_hand(ARVRPositionalTracker.HAND_LEFT)
    var left_hand_position = left_hand_tracker.get_position()
    
    var right_hand_tracker = XRPositionalTracker.new()
    right_hand_tracker.set_type(ARVRServer.TRACKER_CONTROLLER)
    right_hand_tracker.set_hand(ARVRPositionalTracker.HAND_RIGHT)
    var right_hand_position = right_hand_tracker.get_position()

    # Now you can use left_hand_position and right_hand_position to manipulate objects in your XR scene.

Tracking Custom Anchors

Besides controllers, you might want to track custom anchors in space, like a specific location or an object in your AR scene. First, you must set the anchor’s ID.

func _ready():
    var anchor_id = 1  # This ID will be used to reference the anchor
    var custom_anchor_tracker = XRPositionalTracker.new()
    custom_anchor_tracker.set_type(ARVRServer.TRACKER_ANCHOR)
    custom_anchor_tracker.set_anchors_id(anchor_id)

Then you can retrieve the anchor’s position within the _process function just like we did with the controllers.

func _process(delta):
    var custom_anchor_position = custom_anchor_tracker.get_position()
    # Use custom_anchor_position to interact with the tracked anchor in your XR environment.

Responding to Tracking Changes

It’s crucial to respond to changes in tracking state to maintain immersion. You can track whether a controller or anchor loses tracking and handle it accordingly.

func _process(delta):
    var tracker = XRPositionalTracker.new()
    # Let's say we're tracking the left hand controller
    tracker.set_hand(ARVRPositionalTracker.HAND_LEFT)
    
    if tracker.is_active():
        if tracker.get_tracks_status() == ARVRPositionalTracker.TRACKER_TRACKING:
            # Controller is tracking correctly
        elif tracker.get_tracks_status() == ARVRPositionalTracker.TRACKER_LOST:
            # Controller has lost tracking - handle accordingly
    else:
        # Tracker is not active

By testing for these states, you can implement visual feedback or other mechanisms to inform the player of changes in tracking state.

These examples should give you a better understanding of how to use the XRPositionalTracker with Godot 4. As a reminder, it’s important to keep updating and querying your trackers within the _process loop to ensure that your XR experiences respond timely to user movements and interactions.

Enhancing Interactivity with XRPositionalTracker Signals

To create a truly engaging XR application, we must pay attention to how the user interacts with their environment. Godot’s signaling system allows us to handle events such as a controller being identified, or its button being pressed. Here’s how you can set up signals for these events.

First, we connect the relevant signals to our XRPositionalTracker:

func _ready():
    var tracker = XRPositionalTracker.new()
    tracker.connect("tracker_added", self, "_on_Tracker_Added")
    tracker.connect("button_pressed", self, "_on_Button_Pressed")
    tracker.connect("button_released", self, "_on_Button_Released")
    # ...connect other necessary signals

func _on_Tracker_Added(tracker):
    print("A new tracker has been added: ", tracker.get_name())

func _on_Button_Pressed(button_index):
    print("Button pressed: ", button_index)

func _on_Button_Released(button_index):
    print("Button released: ", button_index)

The signals will notify you when trackers are added or when buttons are interacted with. With these callbacks, you can implement logic that responds to these user actions.

Acquiring Controller Orientation

Besides position, orientation is equally important in XR experiences for realistic interaction. Here’s how to obtain the rotation information from a controller:

func _process(delta):
    var controller_tracker = XRPositionalTracker.new()
    controller_tracker.set_type(ARVRServer.TRACKER_CONTROLLER)
    var controller_orientation = controller_tracker.get_orientation()
    
    # Use controller_orientation to rotate items in your scene or to influence the user interface.

The obtained orientation can be a quaternion or a basis, which you can use to orient objects in your scene as per the user’s controller movements.

Implementing Advanced User Interaction

To create more complex interactions, you may want to toggle features or manipulate the scene using button combos. Here’s an example of how you can accomplish that:

var action_button_index = 0
var alternate_action_button_index = 1

func _on_Button_Pressed(button_index):
    if button_index == action_button_index:
        perform_action()
    elif button_index == alternate_action_button_index:
        perform_alternate_action()

func perform_action():
    # Logic for the main action

func perform_alternate_action():
    # Logic for the alternate action

This code allows you to map different functions to buttons on your controller, broadening the interactivity in your application.

Tracking the Position of Spatial UI Elements

Spatial UI elements are a fantastic way to integrate menus and interactive components into your XR experience. Let’s set up tracking for a UI element such as a virtual button panel in 3D space:

func _ready():
    var ui_tracker_id = 2
    var ui_tracker = XRPositionalTracker.new()
    ui_tracker.set_type(ARVRServer.TRACKER_UI)
    ui_tracker.set_anchors_id(ui_tracker_id)

func _process(delta):
    var ui_tracker_position = ui_tracker.get_position()
    update_ui_position(ui_tracker_position)

func update_ui_position(position):
    # Assuming 'ui_panel' is a spatial node representing your virtual button panel
    ui_panel.set_translation(position)

By tracking a spatial UI element, you can ensure that it remains in a fixed position relative to the real world, providing a consistent point of interaction for the user.

These code snippets present the range of possibilities available with the XRPositionalTracker in Godot 4. This powerful tool enables an evolution in your XR design, allowing you to craft believable and interactive worlds that can respond dynamically to user inputs.

Remember that an XR positional tracker’s true power is unleashed when you creatively integrate it into your game logic. We at Zenva encourage you to experiment with these features and to check out our courses for a deeper understanding of Godot and XR development. Happy coding!

In our journey to craft compelling XR experiences, we should explore how to detect the relative movements of controllers to implement mechanics such as object throwing or pushing. By understanding the velocity and angular velocity provided by trackers, we can make our virtual worlds react with natural physics-based interactions.

To begin, let’s calculate the linear velocity of a tracker, which is essential for throwing objects in XR:

func _process(delta):
    var controller_tracker = XRPositionalTracker.new()
    controller_tracker.set_type(ARVRServer.TRACKER_CONTROLLER)
    controller_tracker.set_hand(ARVRPositionalTracker.HAND_LEFT)
    
    # Calculate linear velocity
    var linear_velocity = controller_tracker.get_linear_velocity()
    
    # Use the linear velocity to apply forces to objects in your game world
    if some_condition_to_throw_object:
        thrown_object.apply_impulse(Vector3(), linear_velocity)

The angular velocity of the tracker can also be used to add spin to thrown objects:

func _process(delta):
    var controller_tracker = XRPositionalTracker.new()
    controller_tracker.set_hand(ARVRPositionalTracker.HAND_LEFT)
    
    # Calculate angular velocity
    var angular_velocity = controller_tracker.get_angular_velocity()
    
    # Use the angular velocity for realistic object rotation upon throw
    if some_condition_to_throw_object:
        thrown_object.add_torque(angular_velocity)

Now, let’s explore how to interact with virtual objects using a ‘grab and move’ mechanic. For this purpose, detection of the proximity between the controller and objects and the state of controllers’ buttons are used:

func _process(delta):
    var controller_tracker = XRPositionalTracker.new()
    controller_tracker.set_type(ARVRServer.TRACKER_CONTROLLER)
    
    # Assume we have a function that detects if we're close enough to grab the object
    if is_controller_close_to_grabbable_object(controller_tracker.get_position()) and controller_tracker.is_button_pressed(grab_button_index):
        # Logic to attach the object to our controller's position
        grabbed_object.global_transform.origin = controller_tracker.get_position()

Additionally, to enhance interaction realism, haptic feedback can be used when a user touches or grabs an object in the virtual space:

func _process(delta):
    var controller_tracker = XRPositionalTracker.new()
    controller_tracker.set_hand(ARVRPositionalTracker.HAND_LEFT)
    
    if is_controller_touching_object(controller_tracker.get_position()):
        controller_tracker.trigger_haptic_pulse(strength, duration)

Realism in XR can also be achieved by implementing boundaries within your virtual space that correlate with the real world, often referred to as ‘guardian systems’ or ‘play areas’. Here’s how you can check for these boundary interactions:

func _process(delta):
    var boundary_tracker = XRPositionalTracker.new()
    boundary_tracker.set_type(ARVRServer.TRACKER_BOUNDARY)
    
    if boundary_tracker.get_boundary_type() == ARVRPositionalTracker.BOUNDARY_OUTER:
        # The user is approaching the outer bounds of the play area
        warn_user_of_boundary_approach()

For advanced XR experiences, we may want to tailor the behavior of our systems based on the type of tracked device. Godot provides the ability to get the tracker’s name, which can be used to run specific logic:

func _process(delta):
    var controller_tracker = XRPositionalTracker.new()
    var controller_name = controller_tracker.get_name()

    match controller_name:
        "HTC_Vive_Controller":
            # Specific logic for HTC Vive Controllers
            handle_vive_controller_input()
        "Oculus_Touch_Controller":
            # Specific logic for Oculus Touch Controllers
            handle_oculus_controller_input()
        _:
            # Default logic for other controllers

Through these examples, you’ll see that with Godot’s XRPositionalTracker, you’re not only tracking controllers and anchors but also crafting rich, interactive experiences that delight users by replicating realistic actions and reactions within your virtual worlds.

Keep experimenting with these concepts, and remember to consult the official Godot documentation for more details on functions and classes. At Zenva, we’re passionate about empowering you with the skills to bring your innovative ideas to life. Dive into our comprehensive courses for more immersive learning experiences, and embark on your journey to becoming an accomplished XR developer.

Continuing Your Godot XR Development Journey

Your exploration of the XRPositionalTracker in Godot 4 does not have to end here. As you’ve stepped into the realm of XR development, the path ahead is filled with endless opportunities for creation and learning.

To further your development skills and knowledge, consider delving into our Godot Game Development Mini-Degree. This comprehensive and curated program offers a broad range of topics, from 2D and 3D game creation to mastering the intricacies of GDScript and building robust game mechanics. It’s a perfect next step for anyone looking to expand their Godot expertise, whether you’re a beginner eager to learn or a seasoned developer polishing your craft.

For a broader selection of learning materials, our catalog of Godot courses covers a wide array of subjects. These courses are designed to grow with you on your journey from beginner to professional, allowing you to craft engaging games and possibly lead to exciting career opportunities in game development.

At Zenva, we’re committed to providing high-quality instruction and resources to support your ambitions. With our courses, you’ll be able to learn at your own pace, build a strong portfolio, and take confident steps towards becoming a professional developer. Continue your journey, and start creating the games you’ve always wanted to play!

Conclusion

Embarking on the adventure of XR development in Godot is a journey of creativity and technical prowess. You’ve glimpsed the powerful capabilities of the XRPositionalTracker, a tool that when wielded correctly, can bring depth and dynamism to your virtual worlds. Whether you’re aspiring to create the next hit VR game or looking to innovate within the AR space, the knowledge and skills you’ve uncovered here will serve as a strong foundation for your future projects.

As you continue to discover the potential within Godot 4 and expand your development horizons, we invite you to explore our Godot Game Development Mini-Degree and our versatile range of Godot courses. At Zenva, we’re thrilled to support your growth as an XR developer, and we can’t wait to see where your newfound expertise will take you. Keep learning, keep creating, and let’s shape the future of interactive media together.

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