- Eoin Mcloughlin, Microsoft, mailto:[email protected]
- Rory Mullane, Microsoft, mailto:[email protected]
- George Tian, Microsoft, mailto:[email protected]
- Aaron Franke, Godot Engine, mailto:[email protected]
- Eric Griffith, Meta, mailto:[email protected]
- Janine Liu, Cesium, mailto:[email protected]
- Sean Lilley, Cesium, mailto:[email protected]
Draft
Written against glTF 2.0 spec.
This extension adds data definitions for implicit shapes. This extension does not mandate any particular behaviour for these objects aside from a description of their geometry. These types are to be used in combination with other extensions which should specify the behavior of these types.
This extension provides a set of document-level objects, which can be referenced by objects in a glTF document.
Shapes are defined within a dictionary property in the glTF scene description file, by adding an extensions property to the top-level glTF 2.0 object and defining a KHR_implicit_shapes property with a shapes array inside it.
Each shape defines a mandatory type property which designates the type of shape, as well as an additional structure which provides parameterizations specific to that type. The following example defines a sphere.
"extensions": {
"KHR_implicit_shapes" : {
"shapes": [
{
"sphere": { "radius": 0.1 },
"type": "sphere"
}
]
}
}To describe the geometry which represents the object, shapes must define at most one of the following properties:
| Type | Description | |
|---|---|---|
| sphere | object |
A sphere centered at the origin in local space. |
| box | object |
An axis-aligned box centered at the origin in local space. |
| cylinder | object |
A cylinder centered at the origin and aligned along the Y axis in local space, with potentially different radii at each end. A cone is a special case of cylinder when one of the radii is zero. |
| capsule | object |
A capsule (cylinder with hemispherical ends) centered at the origin and defined by two "capping" spheres with potentially different radii, aligned along the Y axis in local space. |
When the type of a shape refers to a shape type defined by this extension, the shape must not supply a value for a different shape type e.g. a shape whose type is "box" must not have a defined sphere property. Similarly, if type does not reference a shape type declared by KHR_implicit_shapes, an extension or other mechanism should supply an alternate shape definition.
Degenerate shapes are prohibited. A sphere must have a positive, non-zero radius. A box shape must have positive non-zero values for each component of size. The capsule shape must have a positive, non-zero height and both radiusTop and radiusBottom must be positive. A cylinder shape must have a positive, non-zero height, both radiusTop and radiusBottom must be non-negative, and at least one of radiusTop and radiusBottom must be non-zero.
- JSON schema: glTF.KHR_implicit.schema.json
With consideration to the glTF 2.0 Asset Object Model Specification document, the following pointer templates represent mutable properties defined in this extension.
| Pointer | Type |
|---|---|
/extensions/KHR_implicit_shapes/shapes/{}/box/size |
float3 |
/extensions/KHR_implicit_shapes/shapes/{}/capsule/height |
float |
/extensions/KHR_implicit_shapes/shapes/{}/capsule/radiusBottom |
float |
/extensions/KHR_implicit_shapes/shapes/{}/capsule/radiusTop |
float |
/extensions/KHR_implicit_shapes/shapes/{}/cylinder/height |
float |
/extensions/KHR_implicit_shapes/shapes/{}/cylinder/radiusBottom |
float |
/extensions/KHR_implicit_shapes/shapes/{}/cylinder/radiusTop |
float |
/extensions/KHR_implicit_shapes/shapes/{}/sphere/radius |
float |
Additional read-only properties
| Pointer | Type |
|---|---|
/extensions/KHR_implicit_shapes/shapes.length |
int |
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