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
Bones
Animations
- Keyframess
Atlases
Styles
- Textures
Visuals
- Vertex
- Bind
- BindVert
Inverse Kinematics
Physics
Initial Fields
Constructed Bones

Armature

Key	Type	Default	Description
version	String	`""`	Editor version that exported this file
baked_ik	Bool	`false`	Was this file exported with baked IK frames?
img_format	String	`"PNG"`	Exported atlas image format (PNG, JPG, etc)
clear_color	Color¹	Transparent²	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	Styles[]	`[]`	Array of all styles
inverse_kinematics	InverseKinematics[]	`[]`	Array of all bone inverse kinematics data
visuals	Visuals[]	`[]`	Array of all bone visuals (texture, mesh)
physics	Physics[]	`[]`	Array of all bone physics data

Bones

Key	Type	Default	Description
id	Uint	`0`	Bone ID
name	String	`""`	Name of bone
pos	Vec2	`(0, 0)`	Position of bone
rot	Float	`0`	Rotation of bone
scale	Vec2	`(1, 1)`	Scale of bone
parent_id	Int	`-1`	Bone parent ID (-1 if none)
tex	String	`""`	Name of texture to use
zindex	Int	`0`	Z-index of bone (higher index renders above lower)
hidden	Bool	`false`	Whether this bone is hidden
tint	Color¹	White³	Color tint
inverse_kinematics_id	Int	`-1`	Inverse Kinematics ID
visuals_id	Int	`-1`	Visuals ID
physics_id	Int	`-1`	Physics ID

Inverse Kinematics

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

Key	Type	Default	Description
family_id	Uint	`-1`	The ID of family this bone is in (-1 by default)
constraint	String	`"None"`	Constraint (Clockwise, CounterClockwise)
mode	String	`"FABRIK"`	Mode (FABRIK, Arc)
target_id	Uint	`-1`	Target bone ID
bone_ids	Uint[]	`[]`	ID of all bones in this family
mimic_target	Bool	`false`	Should the last bone follow target’s rotation?
init_constraint	String	`constraint`	Initial field for `constraint`⁴
init_mode	String	`mode`	Initial field for `mode`
init_mimic_target	Bool	`mimic_target`	Initial field for `mimic_target`

Visuals

Visual data of each bone (texture & mesh)

Key	Type	Default	Description
tex	String	`""`	Name of texture to use
zindex	Int	`0`	Z-index of bone (higher index renders above lower)
tint	Color¹	White³	Multiplicative color tint for texture
vertices	Vertex[]	`[]`	Array of vertices
indices	Uint[]	`[]`	Each index is vertex ID. Every 3 IDs forms 1 triangle.
binds	Bind[]	`[]`	Array of bone binds
pivot_pos	Vec2	`(0, 0)`	Position of texture pivot
pivot_scale	Vec2	`(0, 0)`	Scale of texture pivot
pivot_rot	[Float]	`0`	Rotation of texture pivot
init_tex	String	`""`	Initial field for `tex`⁴
init_tint	Color¹	White³	Initial field for `tint`
init_zindex	Int	`0`	Initial field for `zindex`

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	Default	Description
id	Uint	`0`	ID of vertex
pos	Vec2	`(0, 0)`	Position of vertex
uv	Vec2	`(0, 0)`	UV of vertex
init_pos	Int	`pos`	Helper for initial vertex position⁴

Bind

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

Key	Type	Default	Description
id	Int	`-1`	ID of bind
is_path	Bool	`false`	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	Default	Description
id	Uint	`0`	ID of vertex
weight	Float	`1`	Weight assigned to this vertex

Physics

Key	Type	Default	Description
global_pos	Vec2	`(0, 0)`	Bone’s position based on physics. Overrides `bone.position` in inheritance()
global_scale	Vec2	`(0, 0)`	Bone’s scale based on physics. Overrides `bone.scale` in inheritance()
global_rot	Float	`0`	Bone’s rotation based on physics. Overrides `bone.rotation` in inheritance()
pos_damping	Float	`0`	Higher damping makes position interpolate slower towards `bone.position`
scale_damping	Float	`0`	Higher damping makes scale interpolate slower towards `bone.scale`
rot_damping	Float	`0`	Higher damping makes rotation interpolate slower towards `bone.rotation`
pos_ratio	Float	`0`	Ranges from -1 to 1. -1-0: less Y, 0-1: less X
scale_ratio	Float	`0`	Ranges from -1 to 1. -1-0: less Y, 0-1: less X
global_orbit	Float	`0`	Bone’s parental orbit based on physics. Overrides `orbitRot` in inheritance()
global_orbit_diff	Float	`0`	Used to offset `global_orbit` by this much when swaying
global_orbit_vel	Float	`0`	Used to calculate velocity when `rot_bounce` is more than 0
sway	Float	`0`	When bone’s parent is moved, how much should this bone sway?
rot_bounce	Float	`0`	Along with sway, makes bone bouncy/wiggly

Animations

Key	Type	Default	Description
id	String	`0`	ID of animation
name	String	`""`	Name of animation
fps	Uint	`0`	Frames per second of animation
keyframes	Keyframes[]	`[]`	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	Default	Description
frame	Uint	`0`	frame of keyframe
bone_id	Uint	`0`	ID of bone that keyframe refers to
element	String	`""`	Element to be animated by this keyframe
value	Float	`0`	Value to set `element` of bone to
value_str	String	`""`	String variant of value
next_kf	Int	`-1`	Index of the next associated keyframe
start_handle	Float	`0.333`	Handle to use for start of interpolation
end_handle	Float	`0.666`	Handle to use for end of interpolation

Atlases

Easily-accessible information about texture atlas files.

Key	Type	Default	Description
filename	String	`""`	Name of file for this atlas
size	Vec2	`(0, 0)`	Size of image (in pixels)

Styles

Groups of textures.

Key	Type	Default	Description
id	Uint	`0`	ID of style
name	String	`""`	Name of style
textures	Texture	`[]`	Array of textures

Textures

Note: Coordinates are in pixels.

Key	Type	Default	Description
name	String	`""`	Name of texture
offset	Vec2	`(0, 0)`	Top-left corner of texture in the atlas
size	Vec2	`(0, 0)`	Append to `offset` to get bottom-right corner of texture
atlas_idx	Uint	`0`	Index of atlas that this texture lives in

Initial Fields

Some fields in Bones, Visuals, Inverse Kinematics, and Physics have init_ counterparts. Their value is duplicated from the original field.

While the original field is modified during animation, init_ fields are used to return the original field back to its initial state (see ResetBones()).

Constructed Bones

An extra set of bones is recommended for optimization in the Construct() generic function. This is a clone of the bones array, but with construction applied to it for use later with Draw().

A variant of Vec4: (red, green, blue, alpha) ↩ ↩2 ↩3 ↩4
Transparent: (0, 0, 0, 0) ↩
White: (255, 255, 255, 255) ↩ ↩2 ↩3
See Initial Fields ↩ ↩2 ↩3

SkelForm Developer Documentation