SkeletonModification2DStackHolder in Godot – Complete Guide

Bringing characters to life with smooth movements and animations is essential for creating engaging games. In Godot 4, a powerful game engine known for its versatility and ease of use, the introduction of the SkeletonModification2DStackHolder adds a new dimension to 2D skeletal animation. This tutorial will delve into the nitty-gritty of leveraging the SkeletonModification2DStackHolder class to enhance your 2D skeletal animations.

Through this journey, you’ll enhance your understanding of Godot’s animation systems and how to apply various modifications to a single skeleton. So whether you’re just starting out or you’re a seasoned developer looking to expand your toolset, this tutorial promises to equip you with valuable knowledge and skills. Let’s dive into the world of 2D animation modifications and discover the magic that can be achieved with the SkeletonModification2DStackHolder.

What is SkeletonModification2DStackHolder?

The SkeletonModification2DStackHolder is an innovative class in Godot 4 that functions as a container for a SkeletonModificationStack2D. This allows developers to apply multiple modification stacks to a single Skeleton2D node. Essentially, it acts as a bridge connecting your modification stack to the skeleton, managing when and how the stack’s modifications are applied.

What is it For?

Imagine your character needing to perform a myriad of actions – from a simple wave to a complex dance routine. The SkeletonModification2DStackHolder is designed to organize and handle multiple animation stacks that can control these actions, all on a single skeleton. It’s a powerful feature for game developers who want to create more dynamic and flexible animations without cluttering their projects with multiple skeletons.

Why Should I Learn It?

By mastering the SkeletonModification2DStackHolder, you gain:

– Enhanced control over your 2D animations.
– The ability to create complex animation layers and blend them seamlessly.
– A more organized and efficient approach to managing multiple animation states.

Learning how to utilize this class expertly will undoubtedly improve the quality of your games’ animations and broaden your skillset within the Godot engine. Let’s harness the full potential of your 2D characters with the help of Godot 4’s SkeletonModification2DStackHolder.

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Setting Up the Skeleton2D Node

Before diving into using the SkeletonModification2DStackHolder, it’s crucial to set up your Skeleton2D node properly. This node serves as the foundation for attaching and manipulating the bones of your 2D character.

var skeleton =

The code above creates a new Skeleton2D instance and then adds it as a child to your scene. With the skeleton in place, you can start adding bones that will define the structure of your character.

skeleton.set_bone_parent("leg", "arm")

This snippet demonstrates how to add bones to your Skeleton2D and assign a parent-child relationship between them.

Creating and Applying the SkeletonModificationStack2D

Now that you have the Skeleton2D set up, it’s time to create a modification stack and assign it to the SkeletonModification2DStackHolder.

var modification_stack =
skeleton.modification_stack = modification_stack

This code creates a new SkeletonModificationStack2D instance and assigns it to the skeleton’s modification stack property. This stack will manage all the modifications applied to the skeleton.


Here, we are adding two different modifications to the stack: a look-at modifier and an inverse kinematics (IK) modifier. These modifiers will alter how the skeleton’s bones behave in response to specific conditions and targets.

Adjusting Modifications Properties

With your modifications in place, adjusting their properties to suit the needs of your 2D character’s animations is essential.

var look_at_mod = modification_stack.get_modification(0) as SkeletonModification2DLookAt
look_at_mod.tracking_speed = 5.0
look_at_mod.enable_bone_rotations = true

This snippet accesses the first modification in the stack, casts it to a SkeletonModification2DLookAt type, and adjusts its properties such as tracking speed and bone rotation enabling.

var ik_mod = modification_stack.get_modification(1) as SkeletonModification2DIK
ik_mod.root_bone = "arm"
ik_mod.target_node = $Target2D
ik_mod.additional_rotation_degrees = 90.0

Similarly, this code accesses the second modification (assuming an IK modifier was second in the stack), casts it accordingly, and sets the root bone, target node, and an additional rotation.

Implementing the SkeletonModification2DStackHolder

Finally, we attach the SkeletonModification2DStackHolder to our skeleton to fully benefit from the stacked modifications.

var stack_holder =
stack_holder.stack = modification_stack

The code above creates a new SkeletonModification2DStackHolder, adds it to the skeleton node, and then assigns our previously created SkeletonModificationStack2D instance to it. This links our modification stack with the skeleton through the holder.

func _process(delta):

Lastly, we ensure the modifications are updated every frame by calling the execute function with the delta time provided by the _process function. This keeps our modifications live and responsive to the game environment.

With these basics, you now have a framework to create and manage detailed animations using the SkeletonModification2DStackHolder in Godot 4. Practice and experimentation with these elements will lead you to master the art of 2D skeletal animation in Godot. Keep playing with these methods to breathe life into your characters in unique and interactive ways!Integrating Interactivity with Your Animations
To make your animations respond to in-game events or player actions, you can modify the properties of your SkeletonModification2D at runtime. This flexibility allows your characters to interact with the environment dynamically.

func _input(event):
    if event is InputEventMouseButton and event.pressed:
        ik_mod.target_position = event.position
        look_at_mod.look_at_position = event.position

In this example, when the player clicks the mouse, both the IK modifier’s target position and the look-at modifier’s look-at position are updated to the cursor’s location. This could be used to make a character look or point at where the player clicks.

Tweening Bone Properties
To create smooth transitions between two states, you can tween the properties of a bone. This is particularly useful for smooth animations and can complement your existing set of modifications.

var tween =
tween.interpolate_property(ik_mod, "additional_rotation_degrees", 
                           ik_mod.additional_rotation_degrees, 0, 
                           1, Tween.TRANS_LINEAR, Tween.EASE_IN_OUT)

Here we create a new Tween instance, add it as a child to the skeleton, and interpolate the additional_rotation_degrees property of our IK modifier from its current value back to 0 over 1 second, with a linear transition and ease-in-out easing.

Applying Modifiers Conditionally
Sometimes you want to apply certain modifications only under specific conditions. For example, you might want a character to only look at an object when it’s close enough.

func _process(delta):
    var distance_to_target = position.distance_to($Target2D.position) = distance_to_target < 500

In the _process function above, we check the distance between the character and the target. If the target is within 500 pixels, we activate the look-at modification; otherwise, we deactivate it.

Combining Modifications for Complex Behaviors
To create complex behaviors, you might need to combine several modifiers in tandem. Remember that the order of your modifications in the stack can significantly affect the final result.

modification_stack.set_modification_active("IK", true)
modification_stack.set_modification_active("LookAt", false)

Perhaps during a specific part of an animation, you want inverse kinematics to take precedence over the character’s look-at behavior. By toggling the active state of your modifications, you can precisely control their influences.


Additionally, if you want to prioritize one modification over another during the stack execution, you can change their order in the stack dynamically with methods like move_up_modification().


Lastly, if you need to reset your skeleton’s pose to its original state (e.g., at the end of an interaction or animation), you can use the reset_bones() method to clear all the current transformations applied by the modifications stack.

By weaving together these code snippets, you will start creating responsive and dynamic skeletal animations in Godot 4, making your 2D games come alive with characters that react fluidly to their surroundings. Practice combining different modifiers, learn how to fine-tune their properties, and watch as your characters perform intricate and responsive animations that captivate your players.Continuing with the intricate aspects of 2D skeletal animation in Godot 4, let’s explore more functionalities that can make our animations even more interactive and lifelike.

Managing Your Animation States
To handle complex animation scenarios, you might want to create a series of animation states that your character can transition between. Godot’s AnimationTree node, in conjunction with SkeletonModification2DStackHolder, can be quite powerful.

var animation_tree =
var state_machine =

animation_tree.anim_player = $AnimationPlayer
animation_tree.root = state_machine = true


The code above sets up an AnimationTree with an AnimationStateMachinePlayback, assigns an AnimationPlayer to it, and activates the tree. We then start the state machine on an “Idle” animation state.

Customizing Modification Execution Order
The order in which your modifications are applied is crucial for getting the desired aesthetically pleasing result. You can specify the execution order of modifiers in the stack.



In this example, we first add the look-at and IK modifiers to the stack and then determine that they should be executed in a First-In-First-Out (FIFO) manner. This ensures that the first modification we added (look-at) is processed before the IK modification.

Adjusting Modifier Influence
Sometimes you might want a modifier to apply its effect partially instead of fully transforming the bones. This often allows for more subtle and natural-looking animations.

ik_mod.strength = 0.8
look_at_mod.strength = 0.5

The strength property controls the influence of the modifier. Here, we’re adjusting the strength of both IK and look-at modifiers so they blend into the animations without overtaking completely.

Binding Animated Properties to Game Logic
You can bind animated properties to respond to real-time game logic, such as health levels or stamina.

func update_character_health(health_percentage):
    var health_bar_mod = modification_stack.get_modification("HealthBar")
    health_bar_mod.bar_fill_percentage = health_percentage

In the example above, we imagine a modification that involves visualizing a health bar. We have a function that updates a property within our health bar modification based on the character’s health percentage.

Synchronizing Modifiers with User Input
For real-time control of modifiers based on player input, you can hook into the _input function of Godot’s scripting API.

func _input(event):
    if event is InputEventMouseMotion:
        var cursor_position = get_global_mouse_position()
        ik_mod.target_position = cursor_position
        look_at_mod.look_at_position = cursor_position

This code sets the target positions for both the IK and look-at modifications to the mouse position as it moves, creating a direct link between user actions and the character’s animations.

There you have additional examples to enhance the responsive and dynamic nature of your 2D skeletal animations. By utilizing these capabilities, you’ll be able to add depth and polish to your game’s characters and environments. These techniques showcase just how versatile and powerful the Godot engine’s tools are when it comes to animation, making it a superb choice for indie developers and professionals alike. Keep experimenting with these features to find the perfect balance for your game’s aesthetic and playstyle.

Where to Go Next with Your Godot Journey

Having explored the depths of 2D skeletal animation with Godot 4, you’re likely feeling more confident and curious about what else you can achieve with this versatile engine. The path to mastering game development is an ongoing journey, and there’s always more to learn. To continue enriching your skills, we invite you to dive into our Godot Game Development Mini-Degree. This comprehensive collection of courses is tailor-made to help you build games from the ground up using Godot 4, providing a structured learning path from beginner to pro, regardless of your starting point.

The Mini-Degree will guide you through a variety of essential topics, from mastering GDScript and controlling gameplay flow, to creating immersive 2D and 3D worlds. With projects spanning different genres—like platformers, RPGs, RTS games, and survival games—you’ll not only learn but also do, turning knowledge into experience and building a robust portfolio along the way. The curriculum is designed to cater both to those just starting out and developers looking to sharpen their skills, complete with live coding lessons and quizzes, all led by experienced game developers.

If you’re eager for a broader look at what we offer for aspiring Godot developers, our suite of Godot courses is sure to have something to spark your interest and propel your learning forward. Keep forging ahead, and leverage the wealth of knowledge these courses offer to become a game development force to be reckoned with. Your next game-changing project awaits!


Embarking on the journey of game development is an exhilarating challenge, and mastering tools like the SkeletonModification2DStackHolder in Godot 4 is a stepping stone to crafting those mesmerizing games that captivate players. Whether you’re animating a fleet-footed rogue or a formidable dragon, the skills you’ve learned here lay the groundwork for bringing your vision to life with fluidity and expression.

Remember, every great developer once started with a single step—or in our case, a single tutorial. Keep iterating, experimenting, and growing your expertise with our Godot Game Development Mini-Degree. Turn those creative sparks into a roaring fire of game development prowess. We’re excited to see the worlds you’ll create and the stories you’ll tell within them!

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