Option for saving 'gltf.extras'

[pairote]

Hello,

According to the glTF 2.0 specification, extras is one of the properties of the root object for a glTF asset. Its purpose is for storing application-specific data. See: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#reference-gltf

This PR adds a new command line flag --extrasPath for specifying the path to a JSON file that contains an object for storing application-specific data. It also adds an option extras for specifying the object when using obj2gltf as a library. The object will be saved to the top-level of the glTF.

Although the type of extras is any which includes primitive types, the discussion on the glTF spec for primitive extras has resolved — extras should be objects as best practice, and primitive extras may be disallowed in the future. See: KhronosGroup/glTF#1120

Best,

[lilleyse]

@pairote before we review can you submit a CLA?

[pairote]

Hi @lilleyse, I just submitted my CLA to cla@agi.com.

[pjcozzi]

Thanks again for contributing, @pairote! We received your CLA.

[samjhill]

can we get this merged? I would love to have this functionality. Thank you!

[samjhill]

@pjcozzi @lilleyse