SplatExtension

The SplatExtension is a deck.gl layer extension that renders ScatterplotLayer points as soft gaussian "splats" instead of hard antialiased disks. It multiplies each fragment's alpha by a radial gaussian falloff from the point's center, so a disk fades to nothing at its rim. Overlapping splats blend into continuous surfaces, which reads as a colored point-cloud / "poor-man's-photogrammetry" look rather than a field of discs.

It is a pure fragment-stage effect — no extra attributes, no uniforms, no CPU cost, and no configuration props.

Installation#

import { SplatExtension } from '@poopdeck.gl/layers';

Usage#

AnimatedPointLayer installs it internally when splat: true (see AnimatedPointLayer.splat), but it can be applied to any ScatterplotLayer directly:

import { ScatterplotLayer } from '@deck.gl/layers';
import { SplatExtension } from '@poopdeck.gl/layers';

const layer = new ScatterplotLayer({
  id: 'splat-points',
  data: myData,

  extensions: [new SplatExtension()],

  getPosition: (d) => d.coordinates,
  getRadius: 8,
  billboard: true,
});

It is stateless — a single shared instance can serve every sublayer of a family.

How it works#

• The fragment shader reads geometry.uv, deck.gl's unit position within the point sprite (0 at the center, 1 at the disk edge), and computes r² = dot(geometry.uv, geometry.uv).
• Alpha is multiplied — never replaced — by exp(-3.0 · r²). At the disk edge (r² = 1) that factor is ≈ 0.05 (nearly transparent rim), giving a soft but still legible dot. The falloff constant is fixed and not exposed as a prop.
• Because it multiplies into the existing alpha, it composes with whatever alpha earlier extensions in the list already wrote — the temporal fade/wake alpha from TimeFilterExtension and the categorical alpha from CategoryColorExtension both survive underneath the splat shaping. Install it after those extensions in the layer's extensions list so it shapes the final alpha.

Pairs well with#

• rgbColorColumns / colorVectorColumn (per-point camera RGB) — overlapping splats colored from projected camera returns read like a photograph sprayed onto the 3D structure.
• A slightly larger radius and a touch of transparency (lower opacity or alpha in fillColor).
• billboard: true, so every splat faces the camera.

Limitations#

• Relies on geometry.uv semantics, so it only applies to ScatterplotLayer (and layers built on it, like AnimatedPointLayer's point sublayers) — not path, polygon, or arc layers.
• The gaussian falloff constant is fixed at build time; there is no prop to tune softness per layer instance.
• Adding a second SplatExtension to a layer that already has one (e.g. passing it via extensions to an AnimatedPointLayer with splat: true) does not error — deck concatenates same-hook injections with no dedup, and the injection body is braced so it stays idempotent, so the falloff simply squares to exp(-6.0 · r²): a tighter, dimmer dot. Install it once.

Source#

packages/layers/src/extensions/splat-extension.ts