spark/docs/performance.md

Performance Tuning

Rendering millions of Gsplats at 60+ fps can be a demanding task, especially for mobile-class GPUs. Each Gsplat is rendered as two triangles that span the footprint of a Gaussian up to sqrt(8) standard deviations (default value) from the center. Each Gsplat is rendered as a transparent object and must be blended back-to-front.

As a quick rule-of-thumb, the following "Gsplat budgets" are recommended:

• Quest 3: 1 million Gsplats or less, not too many Gsplats concentrated in a small area
• Android phone: 1-2 million Gsplats
• iPhone: 1-3 million Gsplats
• Computer: 1-5 million Gsplats (10-20+ million on some desktops)

Each Gsplat incurs overhead in transforming it via SplatAccumulator for sorting and rendering, and at around 1 million Gsplats this becomes a bottleneck on some systems. Unintuitively, when a large number of Gsplats are concentrated in a small area (for example 500K Gsplats from a Trellis object at a small screen scale) they can bottleneck the GPU's rendering and blending ability.

maxStdDev

Adjust ForgeRenderer.maxStdDev (either directly on ForgeRenderer or via constructor options) to a value less than the default Math.sqrt(8). This limits the extent of the Gaussian fall-off, which by default is approx 2.8. For VR a good value is Math.sqrt(5), which is perceptually very similar to the default.