Layer

type Layer = 
  | ScatterLayer<any>
  | AnnotateLayer<any>
  | ArrowsLayer<any>
  | CometLayer<any>
  | HeatmapLayer<any>
  | PositionalHeatmapLayer<any>
  | HexbinLayer<any>
  | KdeLayer<any>;

Defined in: packages/core/src/scene/types.ts:197

The discriminated union of all layer kinds a Scene can draw. Milestone 1 adds Scatter/Annotate, then Arrows/Comet, then Heatmap here; Milestone 2 adds the remaining density layers (positional heatmap, hexbin, KDE). Those four density variants are the ones the SVG renderer deliberately skips — see render/canvas/render-heatmap.ts, the only renderer that reads them, using the same Scene/PixelTransform as everything else.

Erased to any rather than unknown here deliberately: each accessor function's parameter type makes every *Layer<T> invariant in T under strictFunctionTypes, so a concrete ScatterLayer<MyDatum> could never widen to ScatterLayer<unknown> for storage in this heterogeneous array. Individual layer constructors (and the painters, called generically per-layer) stay fully typed in T.