Initial implementation of unified gsplat rendering

[mvaligursky]

• initial implementation of GSplatManager, managing all splats. It only implements a temporary API by passing splats to a constructor, that will be replaced.
• gsplat resorces can generate initial LOD at runtime. Only implemented for uncompressed splats, other splats used a single LOD (so no LOD for now). A better solution will be done.
• work buffer stores all active splats in the scene, allowing global sorting. Only splats used by active LOD as used, which adds support for LOD.
• some small refactoring of existing gsplat shader chunks, to allow their more flexible use. New shaders use those to implement copy of splats of various formats to the work buffer and also their rendering from the work buffer.
• simple hidden example to test the functionality and temporary API. Note that the main uncompressed version of the church.ply is excluded due to its size.
• works on WebGL and WebGPU

All this is subject to much improvements.

[Maksims]

This is a huge step forward for GSplats! 🙏
Are LoDs configurable?

[mvaligursky]

There is a lot of code that is currently commented out, but will be refactored to a useable form in the near future. I'd prefer not to remove it in order to simplify my life.

[willeastcott]

Approving with some comments, but I would suggest that @slimbuck's review is required before merging.

[mvaligursky]

This is a huge step forward for GSplats! 🙏 Are LoDs configurable?

There will be public API with a way to configure this in the future. At this stage it's just a tech drop without any public API. Still very much WIP.

[Copilot]

Pull Request Overview

This PR introduces a unified gsplat rendering system that enables efficient management and rendering of multiple gaussian splats through a centralized work buffer approach. The key changes include a new GSplatManager that coordinates splat rendering, LOD support for better performance at distance, and shader restructuring for flexibility.

• Implements GSplatManager with unified work buffer rendering for all active splats
• Adds runtime LOD generation and management with distance-based level selection
• Refactors gsplat shader chunks into reusable components for different data sources

Reviewed Changes

Copilot reviewed 32 out of 34 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/scene/shader-lib//collections/shader-chunks-.js	Adds new shader chunk exports for unified gsplat rendering
src/scene/shader-lib//chunks/gsplat/vert/gsplat.js	New shader chunks for work buffer data access and modular structure definitions
src/scene/shader-lib/*/chunks/gsplat/frag/gsplatCopyToWorkbuffer.js	Fragment shader for copying splats to work buffer with LOD remapping
src/scene/gsplat/unified/*.js	Core unified rendering system implementation including manager, work buffer, sorting, and LOD
src/scene/gsplat/gsplat-resource*.js	Enhanced with LOD generation and data reordering capabilities
examples/src/examples/gaussian-splatting/lod.example.mjs	Hidden example demonstrating the new unified API

[willeastcott]

Presumably this will be moved to GSplatComponentSystem at some point?

[mvaligursky]

in the follow up PR I have GSplatDirector which manages GSplatManager instances (per camera / layer) as needed.
GSplatManager stays as is.