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Spark 2.0: Streaming 3DGS Worlds on the Web

Spark is World Labs' open-source (MIT) 3D Gaussian Splatting renderer for the web, built on THREE.js + WebGL2. Spark 2.0 was released 2026-04-15 and introduces streaming, Level-of-Detail, and GPU virtual memory. It's the renderer used by this project's web_sota/src/pages/spark-viewer.tsx page.

What's new in 2.0

1. LoD Splat Tree — render N splats per frame regardless of scene size

Splats are organised into a hierarchical tree (leaves = original splats, interior nodes = merged downsampled approximations up to a single root splat). Each frame Spark picks a "slice" through the tree sized to a tunable budget N (platform default 500K–2.5M), giving steady frame rates on scenes with hundreds of millions of splats.

Two tree-construction algorithms ship:

  • tiny-lod — quick, compact, designed for on-demand in-browser construction.
  • bhatt-lod — higher-quality offline (CLI) algorithm using Bhattacharyya distance between splats for merge pairs.

Both are training-free — no reference images needed.

2. .RAD streaming format

Spark 2.0 defines a new file format (.RAD, "radiance field") that stores a precomputed LoD splat tree and supports HTTP Range requests. The viewer can show a coarse ~64K-splat proxy almost instantly and refine progressively as bytes arrive. Use spark build-lod (CLI) to convert .ply / .spz / .splat / .ksplat / .sog to .RAD.

3. Virtual splat paging

A fixed GPU memory pool (default ~16M splats) acts as a page table; 64K-splat pages are swapped in/out via LRU based on what's visible. This lets scenes far larger than GPU memory render smoothly even on phones and Quest 3.

4. Composite LoD worlds

Multiple splat objects can be traversed jointly so Spark picks a globally optimal set of N splats across all of them — useful for stitching independently captured or generated scenes.

Other 2.0 additions

  • ExtSplats — higher-precision 32-byte encoding with float32 centre coordinates (fixes quantisation in large coord systems).
  • ReadableStream loading — multi-GB files no longer need to fit in a single Uint8Array.
  • SparkXr wrapper for WebXR.
  • Experimental covariance-based splats and linear-blend skinning for animated splat characters.
  • Rust core compiled to Wasm, runs in Web Workers so it doesn't block the render loop.

Format matrix

Format Purpose Spark 2.0 support
.RAD Streaming LoD (native 2.0 format) Best — progressive + paging
.SPZ Compact Gaussian splat Full
.PLY Standard splat format (also compressed) Full
.SPLAT / .KSPLAT Alternative compact encodings Full
.SOG Newer splat format Full
.GLB Collision mesh from Marble Loaded as a THREE.js mesh alongside splats

Local asset serving in this project

The bridge exposes GET /api/local-assets/{filename} which serves files from WORLDLABS_LOCAL_PATH (defaults to ~/Downloads). Allowed extensions: .spz, .rad, .ply, .ksplat, .splat.

GET http://localhost:10865/api/local-assets/my-world.rad

Performance knobs (spark-viewer.tsx)

  • maxSplats — the N budget. Raise on desktop, lower on mobile.
  • sortResolution — how often the global depth sort runs.
  • Foveation parameters — bias detail toward the centre of the viewport.

Defaults in this project target desktop "Ultra" (~2.5M splats per frame). If you're testing on a Quest or phone, drop the budget in the viewer config.

Not in Spark 2.0 (contrary to earlier drafts of this doc)

  • No "programmable physics" — Spark renders splats. Colliders are supplied separately by Marble as GLB meshes and driven by whatever physics engine your host scene uses (THREE.js + cannon / rapier / PhysX, or Unity / Blender on export).
  • No automatic material properties on splats — splats encode position/size/orientation/colour/opacity (+ optional SH for view-dependent colour). Any footstep-sound-per-surface logic must be implemented by the host application.

References