data of unknown extensions is destroyed

[qwiglydee]

When a source asset contains unknown extensions, all the related data get lost.

To Reproduce

1. Download Animated Colors Cube from official Khronos sample assets
2. perform npx gltf-transform copy AnimatedColorsCube.glb AnimatedColorsCube.copy.glb
3. compare the files and discover they differ (all data related to KHR_animation_pointer get removed)

According to the statement

glTF Transform provides fast, reproducible, and lossless control of the low-level details in a 3D model.

I would expect that the tool does not destroy unknown data but instead preserves it as is, in the same manner as all extras are preserved.

Versions:

• Version: v4.2.1

[donmccurdy]

Hi @qwiglydee! It is not possible for glTF Transform to process models safely without some understanding of any glTF extension(s) in the file. If the glTF model declares an extension as "required" and glTF Transform doesn't recognize it, then the loading process terminates with an error. If the extension is not required then loading continues with only a warning, ignoring data from that extension.

To preserve unknown or custom extensions that glTF Transform does not provide official implementations for, you'd need to provide an implementation yourself with io.registerExtensions.

See: https://gltf-transform.dev/extensions.

[donmccurdy]

To track support for KHR_animation_pointer, see:

• Support KHR_animation_pointer #1448

I believe implementations of this extension for glTF Transform do exist, but I'm not aware of an open source implementation yet.