JSON Scene File Format

This document describes the structure of scene files that can be loaded by Donut's Scene class.

The scene loader looks at the file extension, and if it's .gltf or .glb, loads that model directly, otherwise treats the input as the custom scene description documented here. So, when Donut-based applications take a scene path on the command line, usually that scene can be either a single glTF model or this scene description.

The loader implementation can be found in Scene.cpp inside the LoadWithThreadPool function and other functions called from there.

1. Top-Level Structure

A scene file is a JSON object with the following top-level properties:

Property	Type	Description
models	array of string	Each string is a path to a model file (e.g., .gltf, .glb), relative to the scene file location. Currently, only glTF 2.0 models are supported.
graph	array of object	See the section on scene graph node objects
animations	array of object	See the section on animation objects

2. Scene graph node objects

The graph section contains an array of node objects, where each node may contain child nodes inside its children property.

Every node object may have the following properties:

Property	Type	Description
name	string	Name of the node
parent	string	Path of the custom parent node, as a sequence of names separated by / starting from the scene root. Normally, graph nodes are attached to their parent node in the JSON structure, but this property allows attaching nodes to anything, including inside scene graphs of the model files.
model	integer	Index into the models array. If specified, an instance of the model is created and attached at this node
translation	3-vector (*)	Translation vector
rotation	4-vector	Quaternion rotation in XYZW format
euler	3-vector	Euler angles in radians (used if rotation is not present)
scaling	3-vector	Scaling vector
children	array of node objects	Child nodes
type	string	Leaf type for custom node content. The custom node types are defined by SceneTypeFactory::CreateLeaf, which user code may override to support more node types

Note (*): The "N-vector" notation means an array of N numbers, or a single number that is broadcasted to every element of the vector.

Additional properties may be specified for leaf nodes, depending on the node type. The default implementation of SceneTypeFactory supports the following node types and their properties:

DirectionalLight

Represents a basic directional light with or without area, shining along the light node's negative Z axis.

Property	Type	Description
color	3-vector	Color of the light, default is white [1, 1, 1]
irradiance	number	Light intensity, defined as illuminance of surfaces lit by the light at normal direction, in lm/m^2
angularSize	number	Angular lsize of the light, in degrees, default is 0

PointLight

Represents a point or spherical light source emitting light in all directions from its position.

Property	Type	Description
color	3-vector	Color of the light, default is white [1, 1, 1]
intensity	number	Light intensity in candela (lm/sr)
radius	number	Light radius in world units, default is 0 (point light)
range	number	Maximum effective range of the light, default is infinite

SpotLight

Represents a spotlight emitting a cone of light from its position with a smooth falloff between the inner and outer angles. The angles are measured from the light node's negative Z axis.

Property	Type	Description
color	3-vector	Color of the light, default is white [1, 1, 1]
intensity	number	Light intensity in candela (lm/sr)
radius	number	Light radius in world units, default is 0 (point light)
range	number	Maximum effective range of the light, default is infinite
innerAngle	number	Apex angle of the inner (full-bright) cone in degrees, default is 180
outerAngle	number	Apex angle of the outer cone in degrees, default is 180

PerspectiveCamera

Represents a perspective camera with specific projection parameters.

Property	Type	Description
verticalFov	number	Vertical field of view in radians, default is 1.0 (57.2 degrees)
aspectRatio	number	Aspect ratio, default is unspecified (automatic)
zNear	number	Near clipping plane in world units, default is 1.0
zFar	number	Far clipping plane in world units, default is no far plane (reverse infinite projection)

3. Animation objects

The animations section contains an array of animation objects, where each object defines animation channels for scene nodes or materials.

For more information, see KeyframeAnimation.cpp

Animation object properties

Property	Type	Description
name	string	Name of the animation
channels	array	Animation channels

Animation channel properties

Property	Type	Description
target	string	Name of a single target node or material:<name>
targets	array of strings	Multiple targets
mode	string	Interpolation mode (step, linear, slerp, hermite, catmull-rom)
attribute	string	Animated property (translation, rotation, scaling, or custom property)
data	array	Keyframes

Keyframe properties

Property	Type	Description
time	number	Keyframe time in seconds
value	number or array	Value at keyframe
inTangent	number or array	Incoming tangent value (Hermite spline interpolation only)
outTangent	number or array	Outgoing tangent value (Hermite spline interpolation only)

4. Example

{
	"models": [
		"glTF-Sample-Assets/Models/Sponza/glTF/Sponza.gltf",
		"glTF-Sample-Assets/Models/BrainStem/glTF/BrainStem.gltf"
	],
	"graph": [
		{
			"name": "Sponza",
			"model": 0
		},
		{
			"name": "DancingRobot1",
			"model": 1,
			"translation": [4, 0, -0.5],
			"scaling": 1.2,
			"rotation": [0, 0.7071068, 0, -0.7071068]
		},
		{
			"name": "DancingRobot2",
			"model": 1,
			"translation": [-5, 0, -0.5],
			"scaling": 1.2,
			"rotation": [0, 0.7071068, 0, 0.7071068]
		}
	]
}