Support for GLTF File Format

[rooomFelix]

Feature Request: Support for GLTF File Format

Summary

I would like to request the addition of support for the GLTF (GL Transmission Format) file format in the Geogram. This enhancement would greatly benefit users by expanding the versatility and usability of the library in modern 3D graphics workflows.

Detailed Description

The GLTF file format, developed by the Khronos Group, has rapidly become the standard for 3D model transmission and interchange. Its efficient, compact representation and compatibility with modern web technologies make it an ideal choice for a wide range of applications, including virtual reality (VR), augmented reality (AR), and real-time rendering.

Key benefits of supporting GLTF in the Geogram include:

1. Enhanced Compatibility: Many 3D content creation tools and engines (such as Blender, Unity, and Unreal Engine) natively support GLTF. By integrating GLTF support, the library would seamlessly fit into existing pipelines, reducing the need for additional conversion steps.
2. Performance Optimization: GLTF is designed for efficient transmission and loading, enabling faster model delivery and improved performance in web and mobile applications. The library can leverage this efficiency to optimize 3D models without sacrificing quality.
3. Wide Adoption: As an open standard, GLTF is widely adopted in the industry. Supporting it would attract a broader user base to the Geogram, fostering a more extensive and active community.
4. Rich Feature Set: GLTF supports PBR (Physically Based Rendering) materials, animations, skins, morph targets, and more. Incorporating these features into the optimization process would enhance the visual fidelity and functionality of the resulting models.

Best regards,
Felix

[BrunoLevy]

Hello,
I have no short-term plan for adding GLTF, but I agree this could be interesting.

In the meanwhile, what you can do is developing a add-on: it is easy to register new file formats for geogram,
you just need write a class that inherits MeshIOHandler and declare it to the system using geo_register_MeshIOHandler_creator.

See mesh/mesh_IO.cpp for examples.

[rooomFelix]

Hello Bruno,

Thank you for your prompt feedback. Yes, I have already reviewed the classes. Unfortunately, I am "only" a JavaScript frontend developer, which explains my somewhat audacious request :) The possibility of using Geogram as a WASM library is very exciting, and this is why I am particularly interested in its application within a WebGL context (and related Frameworks like three.js, babylon.js) and its direct use in the browser.

I look forward to seeing this feature on the roadmap in the future. Your library is very intriguing, and I am excited about its development.

[sebmestrallet]

Hello Felix,

I needed to export glTF assets from my Geogram-based project, and I used the tinygltf C++ lib from @syoyo, which API is very close to the glTF spec.

I you want to develop a glTF writer in C++ by assembling the fields from a GEO::Mesh object, I can send you a code snippet.

However, from a web perspective, Javascript seems sufficient to handle & render glTF assets, see modelviewer.dev (google/model-viewer) or https://3dviewer.net (kovacsv/Online3DViewer)

[ftc26]

ok then it may not be possible if it needs other data structures.
I thought that for each morph channel in a gltf a separate vertices attribute channel is created where the weight are stored as floats. the same for bones.

[sebmestrallet]

Each morph channel stores a separate vertices coordinates list, but weights are not attached to vertices; they are in an independent list, of length nb_channels, see tutorial 018. For an animation (variable weights), each time step stores a list of weights value.

[BrunoLevy]

It would be possible to store the bones in the edges of the mesh and the weights in attributes, but the best way of storing everything is probably to have separate meshes for the bones. This could be implemented as a general function that returns several meshes + the images, and a more minimalistic MeshIO binding that just reads the mesh.

[ftc26]

So i wonder if it is possible to simply transfer features like morph and animation channels. Even if the topology of the mesh changes due to decimate, these attributes have to be adapted. Looks like a more complex task.

[BrunoLevy]

I think that blending weights can be transferred, there might be some subtlety near the joints though ...
Functions to transfer attributes between different meshes are in geogram/mesh/mesh_baking.h
In general, transferring structured information between two different meshes is challenging.

[BrunoLevy]

Hello Sébastien,
Interesting ! If you post the code snippet I'll take a look and see how we could integrate it.