KinematicCollision2D in Godot – Complete Guide

Embarking on the journey of game development, one not only crafts exciting worlds but also delves into the realm of physics and interactions. One of the fundamental aspects of game physics is handling collisions effectively. Knowing when and how your game characters bump into the walls or each other is vital for gameplay mechanics. In Godot 4, a powerful engine that’s been embraced by developers worldwide, we find the nifty KinematicCollision2D class – a tool that doesn’t just report collisions, but also provides rich data about the event.

What Is KinematicCollision2D?

Think of KinematicCollision2D as your in-game collision detective. It’s a class provided by Godot 4 that holds detailed information about the interaction that occurs when your moving game characters (more technically, PhysicsBody2D nodes) encounter obstacles. This class is most often utilized in conjunction with the move_and_collide method to handle these physics-based encounters gracefully and intelligently.

What Is It Used For?

The KinematicCollision2D class plays a crucial role in determining the outcome of a collision. It provides the who, what, and where of collision events, furnishing you with information like the colliding object, its velocity, the collision position, normals, and even the remaining motion. With this data, a developer can decide how a character reacts upon hitting different surfaces, be it sliding, bouncing, or stopping altogether.

Why Should I Learn About KinematicCollision2D?

Imagine creating a platformer game where the player character needs to jump from one platform to another, avoiding obstacles. Without understanding collisions, the character could unrealistically pass through walls or fail to land on platforms. By mastering KinematicCollision2D, you ensure immersive and realistic interactions within your game. Beyond just improving gameplay, knowledge about collision detection is crucial for game performance optimization and is a skill sought after in the game development industry.

Whether you’re a beginner eager to put your first sprite on a path of adventure or an experienced coder looking to refine your game’s physics, understanding KinematicCollision2D can greatly elevate the quality of your game. Let’s dive into some practical examples to see KinematicCollision2D in action!

CTA Small Image
FREE COURSES AT ZENVA
LEARN GAME DEVELOPMENT, PYTHON AND MORE
ACCESS FOR FREE
AVAILABLE FOR A LIMITED TIME ONLY

Getting Started with KinematicCollision2D

First, let’s ensure you have a KinematicBody2D node in your scene. This will be the character or object that we want to move and detect collisions with. We’ll start by writing a simple script in GDScript, Godot’s native scripting language, to move our KinematicBody2D node.

extends KinematicBody2D

# Speed at which our character moves
var speed = 200

func _physics_process(delta):
    var motion = Vector2()
    if Input.is_action_pressed('ui_right'):
        motion.x += 1
    if Input.is_action_pressed('ui_left'):
        motion.x -= 1
    if Input.is_action_pressed('ui_down'):
        motion.y += 1
    if Input.is_action_pressed('ui_up'):
        motion.y -= 1
    motion = motion.normalized() * speed * delta
    move_and_collide(motion)

This code snippet moves our character based on player input and calls the move_and_collide method every frame. Now, let’s handle what happens upon collision.

Handling Collisions

When a collision occurs, move_and_collide returns an instance of KinematicCollision2D, which contains details about the collision. Let’s augment our script to make use of this information.

extends KinematicBody2D

# ... previous code ...

func _physics_process(delta):
    # ... previous input and motion code ...

    var collision = move_and_collide(motion)
    if collision:
        handle_collision(collision)

func handle_collision(collision_info):
    print("Collided with: ", collision_info.collider.name)
    print("Collision position: ", collision_info.position)
    print("Collision normal: ", collision_info.normal)

Through the printed statements inside handle_collision, you will see detailed data output in the console whenever your character comes into contact with another PhysicsBody2D node in the scene.

Responding to Collisions

Knowing about a collision is useful, but we often want our nodes to respond in some way. For example, we can make our character slide along an obstacle instead of stopping dead upon collision.

extends KinematicBody2D

# ... previous code ...

func _physics_process(delta):
    # ... previous input and motion code ...

    var collision = move_and_collide(motion)
    if collision:
        motion = motion.slide(collision.normal)
        move_and_collide(motion)

This adjustment to the _physics_process function uses Vector2.slide with the collision’s normal to calculate a new motion vector that keeps the character sliding along the surface, creating more natural movement.

Reacting Differently to Different Objects

Sometimes, you want your character to react differently depending on the kind of object it collides with. This is where collision layers and masks, along with the collision information, become extremely important.

extends KinematicBody2D

# ... previous code ...

func _physics_process(delta):
    # ... previous input and motion code ...

    var collision = move_and_collide(motion)
    if collision:
        if collision.collider.is_in_group("hazard"):
            print("Ouch! Hit a hazard!")
        else:
            motion = motion.slide(collision.normal)
            move_and_collide(motion)

In this snippet, we’re checking whether the colliding object is part of the “hazard” group. If that’s the case, we print a message to the console. Otherwise, we make our character slide along surfaces as before.

With these principles in place, we have the groundwork to create responsive and engaging game physics. In the upcoming section, we’ll delve further into advanced collision handling and how to make even more nuanced responses to in-game physics interactions.

Great, now that we’ve laid the foundation with basic collision handling, let’s spice things up by adding more advanced techniques to our toolkit. Our character’s physics interactions can greatly benefit from refining how we respond to different kinds of collisions.

Bouncing Off Objects

Sometimes, we might want our character to bounce off an object upon collision. By making use of the collision normal and a ‘bounciness’ factor, we can simulate this kind of interaction:

extends KinematicBody2D

var bounciness = 0.5

# ... previous code ...

func _physics_process(delta):
    # ... previous input and motion code ...

    var collision = move_and_collide(motion)
    if collision:
        var bounce_vector = collision.normal * collision.travel.length() * bounciness
        move_and_collide(bounce_vector)

In this code, when a collision occurs, we calculate a ‘bounce_vector’ using the collision normal and travel vector. Our character will then move in the direction of this new vector, simulating a bounce.

Keeping Score

If our game involves collecting items or scoring points, we can increment a score whenever our character collides with a score-giving object:

extends KinematicBody2D

var score = 0

# ... previous code ...

func _physics_process(delta):
    # ... previous input and motion code ...

    var collision = move_and_collide(motion)
    if collision and collision.collider.has_method("give_score"):
        score += collision.collider.give_score()
        collision.collider.queue_free() # Remove the item
        print("Score: ", score)

Here, we check if the collider has a method named ‘give_score’, which implies it’s an object our character can collect. We call this method to get the points and then remove the object from the scene.

Teleporting Through Portals

In games with teleportation mechanics, we may want our character to move to a new location when colliding with a portal:

extends KinematicBody2D

# ... previous code ...

func _physics_process(delta):
    # ... previous input and motion code ...

    var collision = move_and_collide(motion)
    if collision and collision.collider.is_in_group("portal"):
        global_position = collision.collider.destination_position

Upon collision with an object in the “portal” group, we set our character’s ‘global_position’ to the ‘destination_position’ provided by the colliding portal object.

Avoiding Obstacles with Rays

Beyond collision response, we can prevent collisions before they happen. By casting rays ahead of our character, we can detect potential collisions and adjust the character’s path accordingly:

extends KinematicBody2D

# ... previous code ...

func _physics_process(delta):
    # ... previous input and motion code ...

    var collision = move_and_slide(motion)
    var space_state = get_world_2d().direct_space_state
    var ray_to = global_position + motion
    var result = space_state.intersect_ray(global_position, ray_to)

    if result:
        motion = calculate_avoidance(motion, result.normal)

    move_and_slide(motion)

func calculate_avoidance(motion, normal):
    # Avoid the obstacle based on normal and other factors
    # Placeholder for obstacle avoidance logic
    return motion

This logic utilizes ‘move_and_slide’ for movement, as it’s a more sophisticated movement handling method often preferable for characters. We then check ahead with a raycast, and should it detect something, we adjust the character’s motion considering the normal of the collision.

Finally, advanced collision handling isn’t just about responding correctly to collisions; it’s also about optimizing gameplay to ensure smooth and satisfying player experiences. Using these techniques, game developers can tailor each interaction to fit their game’s specific style and mechanics. Godot’s robust physics engine, combined with your creativity, means the possibilities are virtually endless.

With practice, these concepts will become second nature, and you’ll be crafting responsive and dynamic game environments in no time. Keep exploring, keep testing, and remember: each collision is an opportunity for a new gameplay mechanic.

Excellent, as we continue enriching our game with physics, more complex scenarios often arise. Let’s consider these situations and implement solutions with KinematicCollision2D.

Advanced Jumping and Falling Mechanics

If our game features a platformer character, we need to ensure a robust jumping mechanic. This includes responding correctly when landing on platforms and managing how the character falls, which can involve checking for collisions beneath the character:

extends KinematicBody2D

var jump_speed = -500
var gravity = 1200

# ... previous members ...

var velocity = Vector2()

func _physics_process(delta):
    velocity.y += gravity * delta
    if Input.is_action_just_pressed('ui_accept') and is_on_floor():
        velocity.y = jump_speed

    velocity = move_and_slide(velocity, Vector2.UP)

    if is_on_floor():
        print("Landed!")
    elif velocity.y > 0:
        print("Falling!")

In the above snippet, we have introduced a jumping mechanic using the ‘is_on_floor()’ method to ensure the character can only jump when touching the ground. The character prints “Landed!” upon a safe landing and “Falling!” when descending.

Climbing Slopes

Dealing with varying terrain, like slopes, is another common task. A character should be able to move smoothly up and down a slope without jittering:

extends KinematicBody2D

var max_slope_angle = 40

# ... previous members ...

func _physics_process(delta):
    # ... input and gravity ...

    velocity = move_and_slide_with_snap(velocity, Vector2.DOWN, Vector2.UP, true, 4, deg2rad(max_slope_angle))

Here we use ‘move_and_slide_with_snap’ which helps to keep the character attached to the ground, particularly useful for moving along sloped surfaces without losing contact.

Wall Jumping

In some platformers, characters can perform wall jumps. This requires detecting collisions with walls and responding accordingly:

extends KinematicBody2D

var can_wall_jump = false

# ... previous members ...

func _physics_process(delta):
    # ... input, gravity, and movement ...

    can_wall_jump = is_on_wall()

    if Input.is_action_just_pressed('ui_accept') and can_wall_jump:
        velocity.y = jump_speed
        velocity.x = -velocity.x # Push away from the wall

    velocity = move_and_slide(velocity, Vector2.UP)

The character first checks if it’s touching a wall with ‘is_on_wall()’ which allows utilising walls for jumping, thereby pushing away from the wall to create the jump-off effect.

One-Way Platforms

One-way platforms allow a character to jump through them from below, and land on them from above. This requires tweaking the collision response to be conditional based on the character’s direction:

extends KinematicBody2D

# ... previous members ...

func _physics_process(delta):
    # ... input, gravity, and movement ...

    var collision = move_and_collide(velocity)
    if collision and collision.collider.is_in_group("one_way_platform"):
        if velocity.y < 0:
            ignore_collision(collision)

    velocity = move_and_slide(velocity, Vector2.UP)

func ignore_collision(collision):
    remove_collision_exception_with(collision.collider)

This approach makes use of ‘move_and_collide’ to detect when we bump into a one-way platform, which we identify by its group membership. If the character is moving upwards, we use the method ‘remove_collision_exception_with’ to ignore the collision this frame.

Environmental Effects

Characters might encounter zones like water or mud where their movement speed is affected. To simulate this environment effect on the character, you adjust the movement speed based on the collision data:

extends KinematicBody2D

var base_speed = 200
var current_speed = base_speed

# ... previous members ...

func _physics_process(delta):
    var motion = calculate_motion(delta)
    var collision = move_and_collide(motion)

    if collision and collision.collider.is_in_group("slow_zone"):
        current_speed = base_speed * 0.5 # Reduce movement speed by half in a slow zone
    else:
        current_speed = base_speed

    # ... additional code for movement ...

In the above code, when our character enters a zone marked as ‘slow_zone’, we cut the movement speed in half. Upon exiting the zone, the speed is returned to normal.

Finally, a key part of mastering KinematicCollision2D is understanding the real-world physics you want to simulate and breaking them down into a series of conditional responses and calculations that mimic those interactions.

By learning to combine Godot’s rich set of physics-related nodes and techniques, you’ll be able to create beautifully interactive and believable game worlds. We, at Zenva, are dedicated to helping you learn and master these skills through our comprehensive courses, walking you through the nuts and bolts of practical game development terrain.

Furthering Your Game Development Journey

The path of game development never really ends; there’s always a new skill to master, a new idea to conceptualize, or a new technology to explore. For those yearning to continue their journey in game creation, we invite you to dive into our Godot Game Development Mini-Degree. This program is designed to systematically elevate your skills, with comprehensive courses that will guide you through the intricacies of Godot, from the fundamental principles to the creation of complex game systems.

Each course within the Mini-Degree builds upon the last, ensuring a structured learning experience that can cater to both beginners and those with development experience. You will have the opportunity to work on engaging projects that not only bolster your understanding but also contribute to a portfolio showcasing your capabilities in the field of game development. For an even broader exploration of what Godot has to offer, feel free to peruse our full collection of Godot courses.

At Zenva, we understand the importance of practical knowledge and project-based learning. Our courses are designed with flexibility in mind, allowing you to learn at your own pace and on any device. Whether you’re looking to publish your own games, seeking employment in the games industry, or even starting your own business, the Godot Game Development Mini-Degree can be the stepping stone to achieving your goals. Continue crafting the experiences you’ve always dreamed of and create games that resonate with players around the world.

Conclusion

To conclude, your exploration into KinematicCollision2D and Godot 4 is more than just learning about collision detection; it is about bringing your virtual worlds to life with believability and interactivity. Whether it’s mastering the art of a perfect wall jump, creating intricate platformer mechanics, or ensuring that your game characters interact with their environment in realistic ways, each step you take on this journey equips you with the tools needed to transform your game concepts into engaging, playable realities.

Take that next step with confidence by delving into our Godot Game Development Mini-Degree, and join us at Zenva, where we make it our mission to empower you through learning. With our guidance, watch as your game development dreams metamorphose into the games you’ll share with the world. The power to create is at your fingertips – let’s build something extraordinary together.

FREE COURSES
Python Blog Image

FINAL DAYS: Unlock coding courses in Unity, Godot, Unreal, Python and more.