Add GLFW 3DGRUT viewer with openusd export UI and cropping/editing 3DGS points by BBOX

[tangkangqi]

GLFW Rendered view with BBox clipping and exporting OpenUSD

Open exported USDZ in Omniverse

![View in Omniverse]

[moennen]

Thanks a lot @tangkangqi for this work ! However we are not sure about the value of this third visualizer in the codebase which is adding maintenance work. Could you comment on the requirement for this ? 🙏

[tangkangqi]

Hi @moennen thanks for the response. Sorry I will keep this UI in an experimental branch. Its performance and camera interaction are indeed not as good as the original Polyscope viewer, but it is lightweight and fully decoupled from other modules.

It can also be seen as a small reference implementation for a personal OV extension while NuRec is still closed‑source, for example to help users independently debug and understand 3DGRUT, and to expose features that NuRec does not yet have, such as PPISP.

For the “crop/edit 3DGS points by BBox” part, I plan to add a button the Polyscope UI and raise a new PR. This will enable bounding‑box–based masks or arbitrary segmentation manifold masks editing, and to store better camera settings and point‑cloud‑level scale/transform/rotation, so that scenes open in OV with a reasonable size and view instead of relying only on xform. Noticed our recent work ArtisanGS is already integrated into the Polyscope UI.

[wilsonCernWq]

Hey, thank you for contributing, a small question is, what do you see the main use case for this glfw app? Do you have a specific scenario that would require a glfw backend while our polyscope backend does not fit?

[tangkangqi]

No, it shouldn't replace Polyscope. the only benifits are GLFW is more lightweight, and implementing custom cameras, viewers, and interactions serves as a great practice to deepen understanding of building a DCC pipeline.
Thanks for the reminder. I’ll close this PR and focus on implementing the 'Export USD' and snapshot function directly into Polyscope.