File Structure

The editor exports a unique .skf file, which can be unzipped to reveal:

armature.json - Armature data (bones, animations, etc)
atlasX.png - Texture atlas(es), starting from 0
editor.json - Editor-only data
thumbnail.png - Armature preview image
readme.md - Little note for runtime devs

This section will only cover the content in armature.json.

armature.json
Bones
- Initial Fields
- Inverse Kinematics
- Meshes
  - Vertex
  - Bind
  - BindVert
Animations
- Keyframes
Textures
Cached Bones

`armature.json`

Key	Type	Data
version	string	Editor version that exported this file
ik_root_ids	int[]	ID of every inverse kinematics root bone
baked_ik	bool	Was this file exported with baked IK frames?
img_format	string	Exported atlas image format (PNG, JPG, etc)
clear_color	Color	Exported clear color of atlas images
bones	Bone[]	Array of all bones
animations	Animation[]	Array of all animations
atlases	Atlas[]	Array of all atlases
styles	Style[]	Array of all styles

Bones

Key	Type	Data
id	uint	Bone ID
name	string	Name of bone
pos	Vec2	Position of bone
rot	float	Rotation of bone
scale	Vec2	Scale of bone
parent_id	int	Bone parent ID (-1 if none)
tex	string	Name of texture to use
zindex	int	Z-index of bone (higher index renders above lower)
hidden	bool	Whether this bone is hidden
tint	Vec4	Color ting

Initial Fields

During animation, armature bones need to be modified directly for smoothing to work.

If a bone field is not being animated, it needs to go back to its initial state with initial fields (starting with init_).

bool fields use int initial fields, as animations cannot store boolean values (but can still represent them as 0 and 1)

The following is not an exhaustive list.

Key	Type
init_pos	Vec2
init_rot	float
init_scale	Vec2
…	…

Inverse Kinematics

Inverse kinematics is stored in the root (first) bone of each set of IK bones.

Other bones will only have ik_family_id, which is -1 by default.

Key	Type	Data
ik_family_id	uint	The ID of family this bone is in (-1 by default)
ik_constraint	string	This family’s constraint
ik_mode	string	This family’s mode (FABRIK, Arc)
ik_target_id	uint	This set’s target bone ID
ik_bone_ids	uint[]	This set’s ID of bones

Meshes

Only bones that explicitly contain a mesh, will have building data on it.

Bones with a regular texture rect will omit this, as the building data can be inferred through Texture instead.

Key	Type	Data
vertices	Vertex[]	Array of vertices
indices	uint[]	Each index is vertex ID. Every 3 IDs forms 1 triangle.
binds	Bind[]	Array of bone binds

Vertex

A mesh is defined by its vertices, which describe how each point is positioned, as well as how the texture is mapped (UV).

Key	Type	Data
id	uint	ID of vertex
pos	Vec2	Position of vertex
uv	Vec2	UV of vertex
init_pos	int	Helper for initial vertex position

Bind

Meshes can have ‘binding’ bones to influence a set of vertices. These are the primary method of animating vertices.

Key	Type	Data
id	int	ID of bind
is_path	bool	Should this bind behave like a path?
verts	BindVert[]	Array of vertex data associated to this bind

BindVert

Vertices assigned to a bind.

Key	Type	Data
id	uint	ID of vertex
weight	float	Weight assigned to this vertex

Animations

Key	Type	Data
id	string	ID of animation
name	string	Name of animation
fps	uint	Frames per second of animation
keyframes	see below	Data of all keyframes of animation

Keyframes

Keyframes are defined by their element (what’s animated), as well as either value or value_str (what value to animate element to)

Eg: element: PosX with value: 20 means ‘Position X = 20 at frame’

Key	Type	Data
frame	uint	frame of keyframe
bone_id	uint	ID of bone that keyframe refers to
element	string	Element to be animated by this keyframe
value	float	Value to set `element` of bone to
value_str	string	String variant of value
start_handle	float	Handle to use for start of interpolation
end_handle	float	Handle to use for end of interpolation

Atlases

Easily-accessible information about texture atlas files.

Key	Type	Data
filename	string	Name of file for this atlas
size	Vec2	Size of image (in pixels)

Styles

Groups of textures.

Key	Type	Data
id	uint	ID of style
name	string	Name of style
textures	Texture	Array of textures

Textures

Note: Coordinates are in pixels.

Key	Type	Data
name	string	Name of texture
offset	Vec2	Top-left corner of texture in the atlas
size	Vec2	Append to `offset` to get bottom-right corner of texture
atlas_idx	uint	Index of atlas that this texture lives in

Cached Bones

An extra set of bones is recommended for optimization in the Construct() generic function. This is essentially a clone of the original bone array.

SkelForm Developer Documentation