Draft changes for Shapes and Bounding Volumes in glTF 2.1

[weegeekps]

This PR contains the draft changes for Shapes and Bounding Volumes in glTF 2.1. This PR currently points towards the draft-2.1 branch and should be safe to merge to that branch.

These changes were authored by @lilleyse.

Relevant Issues:

• [glTF 2.1] Shapes #2588
• [glTF 2.1] Bounding Volumes #2587

Summary from Copilot:

Major Additions:

1. Bounding Volumes for Nodes

• Added the boundingVolume property to the node schema, allowing nodes to specify a local-space bounding volume for culling, loading, or other spatial operations. The bounding volume references a shape and can be transformed relative to the node. (F06053e9R1, specification/2.1/schema/boundingVolume.schema.jsonR1-R47)
• Documented how bounding volumes are defined, how they are used in hierarchies (BVH), and best practices for asset authors.

2. Shape Definitions and Registry

• Introduced a new top-level shapes array in the glTF schema, enabling authors to define reusable shape objects.
• Documented the available built-in shape types (box, sphere, capsule, cylinder, plane), their parameters, and requirements for validity.

3. Shape and Bounding Volume Schemas

• Added a general shape.schema.json describing the structure of a shape, including type and type-specific parameters.
• Added individual schemas for each built-in shape type: box, sphere, capsule, cylinder, and plane, each with their own required parameters and validation rules. [1] [2] [3] [4] [5]
• Added a boundingVolume.schema.json describing how a bounding volume references a shape and specifies its transform.

Summary of Most Important Changes:

Bounding Volumes

• Added boundingVolume property to nodes, referencing a shape and specifying transform (rotation, scale, translation). (F06053e9R1, specification/2.1/schema/boundingVolume.schema.jsonR1-R47)
• Documented the usage, best practices, and implementation notes for bounding volumes and bounding volume hierarchies in the glTF spec.

Shape System

• Introduced a top-level shapes array in glTF, allowing reusable, parameterized shape definitions.
• Documented built-in shape types and their parameters, including validation requirements and extension mechanisms.

Schema Additions

• Added shape.schema.json and individual schemas for each built-in shape type (box, sphere, capsule, cylinder, plane) to validate shape definitions. [1] [2] [3] [4] [5] [6]
• Added boundingVolume.schema.json to validate bounding volume definitions and their relationship to shapes.