KinematicCollision3D in Godot – Complete Guide

Navigating through the virtual worlds we create in games requires a firm understanding of how objects interact with one another. Collision detection is a cornerstone of game development; it determines whether our heroes can walk through walls or if they bump into them as expected. One of the key components in the Godot game engine for 3D collision detection is the KinematicCollision3D class. Understanding this class and how to effectively utilize it in your games is vital for any aspiring game developer.

What is KinematicCollision3D?

KinematicCollision3D is a class in the Godot 4 engine designed to hold collision data resulting from the movement of a PhysicsBody3D. Utilizing the robust features of this class, developers can retrieve intricate collision details such as colliding objects, contact positions, and the amount of force exerted.

What is it used for?

This class comes into play when a PhysicsBody3D, like a character or a movable object, navigates through a 3D space using functions like `move_and_collide`. When a collision occurs, KinematicCollision3D objects provide valuable collision information that programmers can harness to calculate movement adjustments, enabling realistic interactions between objects in a 3D environment.

Why should I learn it?

Understanding and implementing KinematicCollision3D effectively plays a critical role in creating immersive and reactive 3D environments. Whether developing a platformer or an exploration game, mastering this class ensures your virtual worlds follow the laws of physics – making your game more believable and enjoyable. Learning to manipulate these collision objects will allow you to fine-tune player controls, create complex interactions with the world, and deliver a more polished gaming experience.

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Handling Basic Collisions

To begin using KinematicCollision3D, we’ll handle a simple collision scenario where our character stops upon hitting a wall. First, let’s move our character using the `move_and_slide` method and check whether a collision has occurred.

extends KinematicBody3D

var velocity = Vector3()
var speed = 10

func _physics_process(delta):
    var direction = Vector3()
    if Input.is_action_pressed('ui_right'):
        direction.x += 1
    if Input.is_action_pressed('ui_left'):
        direction.x -= 1
    if Input.is_action_pressed('ui_down'):
        direction.z += 1
    if Input.is_action_pressed('ui_up'):
        direction.z -= 1
        
    direction = direction.normalized()
    velocity = direction * speed
    
    velocity = move_and_slide(velocity)

If your character collides with any object while moving, `move_and_slide` will automatically handle the collision. For more control over the collision response, use `move_and_collide`.

func _physics_process(delta):
    var collision_info = move_and_collide(velocity * delta)
    if collision_info:
        print("Collided with: ", collision_info.collider.name)

Here, we print the name of the other object involved in the collision after moving the player. This information is available through the `collider` property of the resulting KinematicCollision3D object.

Retrieving Collision Details

Receiving feedback from the collision, such as the position and normal, allows us to make decisions based on these interactions. Let’s extract more details from the collision.

func _physics_process(delta):
    var collision_info = move_and_collide(velocity * delta)
    if collision_info:
        print("Collision Position: ", collision_info.position)
        print("Collision Normal: ", collision_info.normal)

The `position` returns the contact point of the collision, and the `normal` gives us the direction of the surface collided with. With these details, we can, for instance, calculate the reflection vector if we want our character to bounce off surfaces:

func _physics_process(delta):
    var collision_info = move_and_collide(velocity * delta)
    if collision_info:
        velocity = velocity.bounce(collision_info.normal)

The bounce method reflects our velocity based on the collision normal, mimicking a bouncing effect.

Sliding Along Surfaces

In many games, characters slide along walls and obstacles rather than stopping immediately upon collision. We can utilize the returned KinematicCollision3D to enable such behavior.

extends KinematicBody3D

var velocity = Vector3()
var speed = 10

func _physics_process(delta):
    # ... same input handling code ...

    var collision = move_and_collide(velocity * delta)
    if collision:
        if collision.collider.is_in_group("slideable"):
            velocity = collision.remainder.bounce(collision.normal) * 0.1
            move_and_collide(velocity)

If the collided object is part of the “slideable” group, we call `move_and_collide` again with the adjusted velocity.

Handling Slopes and Uneven Terrain

When dealing with slopes or uneven terrain, knowing the exact angle of collision is crucial for smooth movement. Here’s how to calculate the slope angle:

func _physics_process(delta):
    var collision_info = move_and_collide(velocity * delta)
    if collision_info:
        var angle_in_radians = collision_info.normal.angle_to(Vector3.UP)
        var angle_in_degrees = rad2deg(angle_in_radians)
        print("Slope angle in degrees: ", angle_in_degrees)

By comparing the angle of the normal to the `Vector3.UP`, we can decide how our character should react; either by allowing them to walk up the slope, requiring them to jump, or preventing them from climbing steeper inclines.

Remember, these examples build the foundation of understanding how to handle complex collision mechanics in a 3D game environment using Godot. With these basics, you can create richer and more responsive game worlds.By now, we’ve covered handling collisions with static surfaces and sliding along obstacles. However, gaming physics doesn’t stop there. What if we want our character to push objects, interact with them, or even climb stairs? We’ll dive into more complex uses of KinematicCollision3D to add depth to our game’s physics.

When it comes to pushing objects, we need to check if the object we’ve collided with can be moved. We verify this by determining whether it has a script with a function for pushing, like so:

func _physics_process(delta):
    var collision_info = move_and_collide(velocity * delta)
    if collision_info and collision_info.collider.has_method("push"):
        collision_info.collider.push(collision_info.normal)

In this example, if the collider has a `push` method, we’re calling it with the direction of the collision. This method would generally be found in a script attached to the pushable object, like so:

var push_strength = 5

func push(direction):
    position += direction * push_strength

Next, let’s handle interactions. Suppose when our character walks over a certain object, such as a coin or a power-up, we want something to happen. We can accomplish this by detecting the type of the collider.

func _physics_process(delta):
    var collision_info = move_and_collide(velocity * delta)
    if collision_info and collision_info.collider is Coin:
        collision_info.collider.collect()

In this situation, if our character collides with a `Coin` instance, we call the `collect` method, which presumably handles logic such as updating the score and removing the coin from the game world.

Handling stairs or stepped terrain can often be tricky. We want our character to automatically climb small steps without jumping. To achieve this, we’ll check for a collision and then try moving upward:

func _physics_process(delta):
    var collision_info = move_and_collide(velocity * delta)
    if collision_info:
        # Try to step up if we hit a small obstacle.
        var step_up = collision_info.normal.slide(Vector3.UP) * -STEP_HEIGHT
        if not move_and_collide(step_up):
            move_and_slide(Vector3.UP * -STEP_HEIGHT)

In this snippet, `STEP_HEIGHT` would be a constant defining how high the character can step. We first attempt to move upward by the step height, and if there’s no collision, we then move forward.

To complete the processing for steps, we also need to ensure the character steps down after stepping up:

if is_on_floor():
    var step_down = Vector3.DOWN * STEP_HEIGHT
    move_and_collide(step_down)

This ensures that if there’s empty space in front of our character after they’ve stepped up, they can step back down onto the ground.

Lastly, let’s talk about gravitational pull. In most games, characters are affected by gravity continuously. Here, we’d update the `velocity` to simulate gravity before moving the character:

func _physics_process(delta):
    velocity.y += GRAVITY * delta
    
    if Input.is_action_just_pressed('ui_select'):
        velocity.y = JUMP_FORCE
    
    velocity = move_and_slide(velocity, Vector3.UP)

Here, `GRAVITY` is usually a negative constant, such as -9.8, representing the force pulling our character down each second, and `JUMP_FORCE` is a positive number that’s applied when the character jumps, momentarily countering gravity.

In summary, the intricacies of KinematicCollision3D are numerous, and mastering them is key to crafting polished and physics-accurate 3D games in Godot. With practice and experimentation, these concepts will become second nature, enabling you to weave real-world physics into your enthralling game worlds.As we delve further into the capabilities of KinematicCollision3D, we begin to explore even more dynamic interaction possibilities. From responding to collision angles to overcoming obstacles, let’s examine additional code snippets that demonstrate these principles in action.

Detecting the angle of a collision can lead to diverse outcomes. For instance, a character may slide off a surface if the angle is too steep or they may lose health upon impact. Here’s how we might handle this:

var max_slope_angle = 45

func _physics_process(delta):
    var collision_info = move_and_collide(velocity * delta)
    if collision_info:
        var collision_angle = rad2deg(collision_info.normal.angle_to(Vector3.UP))
        if collision_angle > max_slope_angle:
            velocity = Vector3.ZERO # Stop the character's movement.
            # Implement additional logic such as damaging the character

This snippet computes the angle at which the character hits a surface and stops their motion if the angle exceeds the predefined slope threshold.

Another interesting use-case of collision detection is triggering environment changes, such as opening doors or activating switches when the player collides with them:

func _physics_process(delta):
    var collision_info = move_and_collide(velocity * delta)
    if collision_info and collision_info.collider is Door:
        collision_info.collider.open()

Upon colliding with a Door instance, we simply call its `open` method, which would contain the logic for animating the door opening.

Let’s not forget the role of KinematicCollision3D in multiplayer scenarios, where you might want to react to collisions with other players or NPCs differently than you would with inanimate objects:

func _physics_process(delta):
    var collision_info = move_and_collide(velocity * delta)
    if collision_info and collision_info.collider is Player:
        # Handle player versus player collisions, e.g. tackle, push back, etc.

Here we check if the collided entity is another Player, which could potentially trigger a custom reaction, like a tackle or push effect.

There may also be occasions where we want to maintain a reference to the last object our character collided with. This could be beneficial for implementing mechanics such as sticky surfaces or grabbing hold of movable objects:

var last_collided_object = null

func _physics_process(delta):
    var collision_info = move_and_collide(velocity * delta)
    if collision_info:
        last_collided_object = collision_info.collider

Storing `last_collided_object` allows us to perform checks or actions upon it later in our code, such as releasing or applying additional forces.

Moreover, when developing platformer games or similar genres, you may also want to make characters jump only if they are on the ground. The `is_on_floor()` method becomes handy in this context, preventing players from air-jumping:

func _physics_process(delta):
    velocity.y += GRAVITY * delta
    
    if Input.is_action_just_pressed('ui_select') and is_on_floor():
        velocity.y += JUMP_FORCE
    
    velocity = move_and_slide(velocity, Vector3.UP)

This ensures that the jump is executed only when the character is on the ground, creating a more realistic and controlled jumping mechanism.

Armed with these insights into Godot’s KinematicCollision3D features, game developers can unleash their creativity to craft interactive gameplay elements that impress and engage players. Each project may present unique challenges, but with a solid understanding of physics-based interactions, the possibilities are nearly endless.

Where to Go Next

Congratulations on diving into the world of 3D collision detection with Godot’s KinematicCollision3D! As you continue to refine your skills and build more complex games, remember that a journey in game development is one of ongoing learning and exploration.

To keep the momentum going and expand your Godot expertise, consider enrolling in our Godot Game Development Mini-Degree. This comprehensive course collection guides you through the process of creating cross-platform games using the Godot 4 engine. You’ll gain hands-on experience with 2D and 3D assets, master GDScript, and understand the intricacies of game mechanics across various genres like RPG, RTS, and platformers.

For a broader look at what we offer, our Godot courses cater to all skill levels, providing flexible and accessible content to fit your learning style. Our project-based approach equips you with practical knowledge to forge a path in the game development industry. Elevate your game creation journey with us, and turn your vision into a playable reality.

Conclusion

Understanding KinematicCollision3D in Godot is akin to unlocking a new dimension in your game development toolkit. With the power to manipulate physics and create realistic interactions, your games will captivate players with their immersive and tactile environments. But your journey doesn’t end here—it’s just the beginning. As you brew more intricate game mechanics and storylines, remember that we at Zenva are here to support and inspire your growth every step of the way.

Keep challenging yourself, keep innovating with new ideas, and above all, keep coding with passion. Rediscover tutorials, refine your skills, or start fresh with a new project by exploring our Godot Game Development Mini-Degree. This is your invitation to join us at Zenva, where the next level of your game development adventure awaits. Let’s create, learn, and grow together in the exciting world of game development!

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