EasyIK

EasyIK is a universal 2D inverse-kinematics addon for Godot 4. It adds a single node—EasyIKManager—that can run any of four IK modifications, chosen from one selector in the inspector: 2DLookAt, 2DCCDIK, 2DFABRIK, and 2DTwoBoneIK.

Unlike Godot's built-in SkeletonModification2D stack, EasyIK stays correct when your character is mirrored with scale.x = -1—the exact scenario where native 2D IK deforms limbs. It captures the transform determinant each frame and folds that flip factor into every bone-angle term, so a mirrored rig bends exactly like the un-mirrored one, per-joint angle limits included.

You pick a modification, assign a target, build the bone chain in a dedicated window, and EasyIK rotates the bones to reach the target every frame—no per-limb sign flipping, no duplicate left/right rigs.

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📑 Table of contents

• Features
• Requirements
• Installation
• Quick start
• Documentation
• Project layout
• Changelog
• Credits

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✨ Features

Single universal node	One EasyIKManager picks its algorithm from a dropdown; the inspector shows only the fields that mode needs.
Four modifications	2DLookAt (aim one bone), 2DTwoBoneIK (analytic arms/legs), 2DCCDIK and 2DFABRIK (N-bone chains).
Flip-safe by design	Correct under scale.x = -1, including per-joint angle limits—the reason the addon exists.
Bone-chain manager	A dedicated editor window to add / remove / reorder joints and pick each Bone2D from the scene tree, with full undo/redo.
Per-joint angle limits	Min / max, invert, local/global space—like native CCDIK constraints, with a live wedge gizmo.
Soft IK	softness eases the approach to full extension, killing the classic IK "pop."
Smooth target follow	target_tracking_delay follows the target with a critically-damped spring (frame-rate independent).
Customizable gizmo	Colors, line widths and sizes exposed in the inspector for bones, joints, target and constraint wedges.
Editor integration	Plugin registers the EasyIKManager node type and the Manage Bone Chain inspector window on enable.
No autoload, no runtime deps	Pure node addon—enable the plugin and add the node.

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📋 Requirements

Item	Required?	Notes
Godot 4.6+	Yes	Developed and tested on Godot 4.6+ (see plugin.cfg). 2D only.
A Skeleton2D + Bone2D chain	Yes	The bones EasyIK rotates. A single Bone2D is enough for 2DLookAt.
A Node2D target	Yes	The point each chain reaches toward—often keyed by an AnimationPlayer.

Expected install path in your project:

res://addons/easyik/

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📦 Installation

1. Copy this repository's addons/easyik folder into your Godot project under res://addons/easyik/.
2. Open Project → Project Settings → Plugins.
3. Enable EasyIK — the editor registers the EasyIKManager node type and the inspector integration (see plugin.gd).
4. Add an EasyIKManager node to your character and configure it in the inspector.

No code or autoload required. The node registers via class_name; you only write code if you want to move targets or tweak EasyIK at runtime.

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🚀 Quick start

1️⃣ Add a target

Create a Node2D where the tip of the limb should reach (e.g. armTarget) and place it where the hand currently is.

2️⃣ Add the EasyIKManager

Add an EasyIKManager node to your character. In the inspector:

• Modification Type → 2DTwoBoneIK
• Target → drag your armTarget

3️⃣ Build the bone chain

Click Manage Bone Chain (in the Bone Chain group). In the window:

1. Click ＋ Add Joint and assign the first bone (e.g. shoulder).
2. Click ＋ Add Joint again and assign the second bone (e.g. arm).

The summary shows shoulder → arm. The limb now reaches toward the target. If the elbow bends the wrong way, tick Flip Bend Direction.

4️⃣ Drive the target

Key the target's position in an AnimationPlayer, or move it from code:

extends Node2D

@onready var arm_target: Node2D = $armTarget

func _process(_delta: float) -> void:
    # Make the hand follow the mouse.
    arm_target.global_position = get_global_mouse_position()

5️⃣ Flip the character correctly

Apply scale.x = -1 to a plain Node2D wrapper that holds the skeleton and the targets—not to a CharacterBody2D (physics recomposition corrupts a mirrored transform). EasyIK keeps every limb and angle limit mirrored cleanly:

extends CharacterBody2D

@onready var visual: Node2D = $Visual   # holds Body + Bones + IKTargets
var _facing := 1

func _flip(direction: float) -> void:
    if direction == 0.0: return
    var f := signi(int(direction))
    if f != _facing:
        _facing = f
        visual.scale.x = f

(Full field reference, the four modifications, joint limits and use-case recipes live in the docs.)

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📚 Documentation

The official documentation is a website:

Open EasyIK Official Documentation in your browser for the full interactive docs (section navigation, EN / ES language toggle, and quick search).

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🗂 Project layout

addons/easyik/
├── plugin.cfg                        # Plugin metadata
├── plugin.gd                         # EditorPlugin: registers the inspector plugin
├── core/
│   └── ik_enums.gd                   # EasyIKEnums: ModificationType, IKProcessMode
├── nodes/
│   ├── easy_ik_manager.gd            # EasyIKManager node — the four solvers + gizmo
│   └── editor/
│       ├── ik_inspector_plugin.gd    # Swaps chain fields for the "Manage Bone Chain" button
│       ├── ik_chain_button.gd        # Inspector button that opens the window
│       └── ik_chain_manager_window.gd# Add / remove / reorder joints + per-joint limits
├── icons/
│   └── icon_easy_ik.svg              # Node icon
└── webSite/                          # Documentation website (EN / ES)

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📝 Changelog

v1.0.0

• Initial public release.
• EasyIKManager node with four selectable modifications: 2DLookAt, 2DCCDIK, 2DFABRIK, 2DTwoBoneIK.
• Flip-safe solvers — correct bone rotations under scale.x = -1 via determinant-based orientation, writing global_rotation directly.
• Manage Bone Chain window — explicit ordered joint list with scene-tree bone picker, reordering, removal, solver iterations, and full undo/redo.
• Per-joint angle limits — min / max, invert, local/global space, flip-invariant (measured in the parent bone's frame), with a live wedge gizmo.
• Soft IK (softness) and a critically-damped target tracking delay (target_tracking_delay).
• Customizable gizmo — colors, line widths and sizes for bones, joints, target and constraint wedges.

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🙏 Credits

• EasyIK — IUX Games, Isaackiux · version 1.0.0 (see plugin.cfg).
• Solver flip-handling technique inspired by the determinant-based approach used in community 2D IK addons.