SkeletonModificationStack2D in Godot – Complete Guide

SkeletonModificationStack2D is a powerful class in Godot 4, opening up remarkable possibilities for 2D skeleton animation. If you’re looking to enhance the fluidity and responsiveness of your character animations in Godot, understanding the SkeletonModificationStack2D resource is essential. Whether you’re an early stage learner eager to dive into the world of game development or a seasoned developer looking to up your game in 2D animation, this tutorial is tailor-made to guide you through the intricacies of the Godot 4 animation system.

Diving deeper into Godot’s animation capabilities, you will see how the SkeletonModificationStack2D can be your backstage crew, setting the scene for your virtual puppets to perform with precision and life-like motion. Let’s unravel the concepts and practical applications of this fascinating feature together!

What is SkeletonModificationStack2D?

The SkeletonModificationStack2D in Godot 4 acts as a reservoir holding a variety of SkeletonModification2Ds. Essentially, it’s a resource attached to a Skeleton2D that maintains a collection of modifications, influencing how your skeleton behaves and animates in 2D space. Consider it a choreographer, orchestrating different moves to create a seamless dance for your characters.

What is it for?

This resource comes into play when there is a need to apply multiple transformations to your Skeleton2D. It delicately controls the sequence and application of these modifications. For instance, in a humanoid character, you’ll discover that making adjustments to the spine before the limbs leads to more natural movements—an ideal setup for full-body inverse kinematics (IK) animations.

Why Should I Learn It?

Mastering the SkeletonModificationStack2D equips you to:

– Create more sophisticated and believable animations
– Have granular control over animated sequences
– Effortlessly implement full-body IK on your characters
– Enhance the user experience through lifelike motion

Learning this class also gives you an additional edge as a game developer. The skills you gain are not just restricted to Godot; they are fundamental to understanding 2D skeletal animation across different platforms. So, let’s roll up our sleeves and begin animating with Godot 4’s SkeletonModificationStack2D.

CTA Small Image

Setting Up a Basic Skeleton2D

To utilize the powers of SkeletonModificationStack2D, we first need to set up a basic Skeleton2D structure. Here’s a simple example of how that looks in Godot’s GDScript:

var skeleton =

This snippet creates a new Skeleton2D node and adds it as a child to the current scene. But a skeleton isn’t much without bones, so let’s add some:

var bone =
skeleton.set_bone_parent(bone.get_index(), -1) # -1 indicates no parent, so it's a root bone

Now, we’ll create a second bone and set the first bone as its parent:

var child_bone =
skeleton.set_bone_parent(child_bone.get_index(), bone.get_index())

Our basic skeleton structure is now in place, ready for more advanced modification.

Initializing the SkeletonModificationStack2D

With our skeleton set up, the next step is to initialize the SkeletonModificationStack2D and attach it to the Skeleton2D:

var modification_stack =
skeleton.set("modification_stack", modification_stack)

We’ve created a new SkeletonModificationStack2D and assigned it to our skeleton. But for now, it’s an empty stack. Time to add some modifications!

Adding Modifications to the Stack

Here, we’ll add a simple Transformation2D modification to our stack. This will allow us to manipulate the bones’ positions directly:

var transform_mod =

transform_mod.set_bone_name("Bone2D") # Specify the bone you wish to modify.
transform_mod.translation = Vector2(10, 0) # This will move the bone 10 pixels on the X-axis.

This code places a Transformation2D modification into our stack which targets a bone named “Bone2D” and shifts it slightly to the right.

Tweaking the Modifications

In the real world, skeletons are flexible, and so is the SkeletonModificationStack2D. Let’s change the modification in real-time:

# Let's rotate our bone by 45 degrees.
transform_mod.rotation_degrees = 45

# And now, let's scale it down a bit.
transform_mod.scale = Vector2(0.8, 0.8)

With the above tweaks, our targeted bone will not only shift position but also rotate and scale. The stack ensures these modifications occur in order without overlapping each other.

And there you have it, the basics of adding and manipulating modifications within a SkeletonModificationStack2D in Godot 4. These examples covered initial setup, stack initialization, adding a modification, and real-time tweaking. Stay tuned to explore even more capabilities of the SkeletonModificationStack2D in the next part of this tutorial!Let’s delve deeper into making our SkeletonModificationStack2D even more dynamic by exploring other types of modifications and how they can be put to use.

Applying Inverse Kinematics (IK)

Inverse Kinematics is a pivotal element in animation, allowing for more natural movements by calculating the necessary angles of joints. Here’s how you can set up an IK modification in our stack:

var ik_mod =

ik_mod.set_chain_length(2) # This includes the parent bone

In this code, an IK modification is created aimed at the “ChildBone2D” and will try to reach the position of a node called `$IKTarget`, which should be somewhere in your scene. This will affect both the bone and its parent, creating a chain-reaction movement.

Adjusting Stack Execution

Sometimes, the order and manner of modification execution can impact the animation. To control the stack execution, use the following commands:

# Disable a specific modification without removing it

# Re-enable the modification

# Prioritize a specific modification by ordering it first
modification_stack.set_modification_order(0, 1)

These lines of code show how to activate and deactivate modifications and change their priority, thus affecting the animation outcome.

Using Custom Modifications

What if you need a modification that isn’t provided by default? Godot allows you to create custom modifications. You’ll need to create a script that extends `SkeletonModification2D`.

extends SkeletonModification2D

func execute(modification_stack):
    # Your custom modification code goes here

After defining your custom modification, you can add it to your stack just like the built-in ones:

var my_custom_mod = preload("res://").new()

By using these examples, we can express creativity in animation with unlimited potential. Remember that these modifications are updated every frame, so you can create dynamic, real-time effects or responsive game mechanics.

Applying Blend Shapes

You can also integrate blend shapes for 2D sprites if you’re working with a `Sprite2D` with a `MeshInstance2D`. This allows for subtle changes in expressions or features.

var blend_shape_mod =

# Let's say you want to adjust the 'Smile' blend shape
blend_shape_mod.set_blend_shape_weight("Smile", 1.0) # This will set the 'Smile' blend shape to its full value.

Using blend shapes within your SkeletonModificationStack2D can add that additional layer of depth to your characters, allowing for smooth transitions between expressions.

In conclusion, Godot’s SkeletonModificationStack2D resource offers a virtual sandbox for animators and game developers to play around with their character’s bones, giving them unprecedented control over the look and feel of their animations. With the capability to affect bones through direct manipulation, inverse kinematics, custom behaviors, and even blend shapes, the SkeletonModificationStack2D can bring your 2D characters to life in compelling and dynamic ways. Whether you’re adding subtle expressions or orchestrating complex movements, these tools are essential for creating responsive and immersive game experiences.Continuing our deep dive into the capabilities of the SkeletonModificationStack2D in Godot 4, let’s enrich our animations with more complex examples that further showcase the adaptability of this tool.

Mixing Animations with Blend2D

The Blend2D node can be used to blend animations together based on a two-dimensional parameter, typically for ‘direction’ and ‘speed’. Here’s a breakdown of how this would be set up:

var blend2d_mod =

# Assuming you have animations 'Walk' and 'Run' in X-axis, and 'Idle' in Y-axis
blend2d_mod.set_blend_point_position(0, Vector2(0, 1)) # Idle
blend2d_mod.set_blend_point_position(1, Vector2(1, 0)) # Walk
blend2d_mod.set_blend_point_position(2, Vector2(2, 0)) # Run

blend2d_mod.set_blend_position(Vector2(1, 0)) # This will play 'Walk'

Adjusting the `blend_position` dynamically, e.g., based on a character’s speed, allows for a smooth transition between ‘Idle’, ‘Walk’, and ‘Run’ animations. This flexibility enhances the character’s animation, leading to more believable movement.

Applying Look-at Modifications

A common animation requirement is for a character to “look at” a target. Here’s how to make a head bone rotate to follow a target node:

var lookat_mod =

lookat_mod.set_additional_rotation_degrees(-90) # Adjusts the angle if the 'look at' is off.

The `LookAtTarget` node can be moved around, and `HeadBone2D` will rotate to follow it, creating the effect of the character gazing towards the target.

Importance of Modifier Stack Execution Order

The order in which modifications are applied is crucial. For instance, you might want an IK to solve before a Look-At modification. Here’s how to adjust the order dynamically:

# Swap the order of IK and LookAt modifications

Or to move it back:


Understanding and controlling the modification order is vital to achieving the intended result in your animation.

Using Script to Dynamically Adjust the Stack

With scripting, you can dynamically modify the stack in response to gameplay. Here’s an example where we use a player’s health to influence a modification:

# Assuming the character fades when health is low
if player_health < 20:
    blend_shape_mod.set_blend_shape_weight("Fade", 0.5)
    blend_shape_mod.set_blend_shape_weight("Fade", 0.0)

This block adjusts the blend shape named “Fade” based on the player’s health, a practical example of modifying your animations based on game events.

Combining Transformations

Sometimes, combining transformations such as scale, rotation, and translation can mimic physical interactions, for instance, simulating recoil:

# Apply a recoil effect
transform_mod.translation += Vector2(-5, 0) # Move the bone backwards
transform_mod.rotation_degrees += 5 # Rotate slightly

In the next frame, reverse the action to return to the initial position:

transform_mod.translation -= Vector2(-5, 0)
transform_mod.rotation_degrees -= 5

This simulates a vibration effect which can enhance the feeling of force or impact.

These additional examples give a deeper understanding of the practical applications of SkeletonModificationStack2D and its potential in creating advanced animations. Creative utilization of such tools can significantly boost the realism and responsiveness of your in-game characters, providing players with a more immersive experience. With Godot 4, such intricate nuances in animation are within reach, empowering developers and animators to push the boundaries of 2D gaming.

Where to Go Next in Your Godot Journey

You’ve dipped your toes into the vast ocean of Godot features with the SkeletonModificationStack2D in Godot 4, but this is just the beginning. If you’re eager to continue expanding your knowledge and skills in Godot, our Godot Game Development Mini-Degree is the perfect next step to elevate your game development journey.

Our comprehensive course collection covers a spectrum of essential topics, from GDScript fundamentals and gameplay mechanics to in-depth explorations of 2D and 3D environments. Designed to cater to beginners and to those who already possess a foundational understanding, the Mini-Degree allows you to learn at your own pace, with project-based lessons that ensure practical experience in building games across multiple genres.

Looking for an even broader range of Godot expertise? Check out Zenva’s full catalog of Godot courses to find the perfect match for your learning goals. Whether you’re looking to create stunning RPGs, intricate RTS games, or engaging platformers, our Godot courses are a treasure trove of knowledge, tips, and best practices. Continue your education with us at Zenva, and take your game development skills to professional heights. The world of Godot awaits, and we’re here to guide you every step of the way.


Embarking on your Godot journey opens up a realm of possibilities in game development, and mastering animation tools like SkeletonModificationStack2D is a step toward bringing your imaginative worlds to life. The key is not just understanding the tool but leveraging it to create games that resonate with audiences. Remember, the only limit is your creativity—and with Godot 4, even the sky isn’t the limit.

If you’re ready to transform your passion into reality, dive deeper into Godot with our Godot Game Development Mini-Degree. Forge ahead, enhance your skills, and be part of a community of creators who share your ambitions. With our Mini-Degree, you’re not just learning to code; you’re crafting experiences that could captivate gamers around the world. Turn today’s learning into tomorrow’s creations with Zenva, your ultimate learning companion on this exciting adventure.

Python Blog Image

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