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Plotting internals

The charts engine, the data-builder and renderer split, and the WebGL layer.

The plotting stack is three packages, layered so that the dependency-free core never pulls in a heavy dependency and the WebGL layer is fully optional.

@mcmcjs/charts     dependency-free engine: terminal + SVG (+ ./dom uPlot)
       ^
@mcmcjs/plots      MCMC data builders + terminal/SVG/HTML renderers
       ^
@mcmcjs/plots-gl   regl WebGL renderers (optional peer)

@mcmcjs/charts: the engine

A small, dependency-free plotting engine that renders a renderer-agnostic figure model. It is domain-neutral: it knows about scales, axes, frames, canvases, and plot primitives, not about MCMC.

  • Terminal — DotCanvas (a braille 2x4 dot grid with set, line, and per-series colored rows, plus a plain-ASCII mode), axisFrame, sparkline, and blockBar.
  • SVG — svgFrame and primitives (svgPolyline, svgRect, svgLine, svgCircle, svgText), plus stackSvg to compose figures.
  • Scales and helpers — linearScale, niceDomain, ticks, fmtNum, extent, the PALETTE / seriesColor palette, and the viridis colormaps.

Color is injected by the caller (a ColorFn), so the core pulls in no runtime dependencies. A separate browser-only subpath, @mcmcjs/charts/dom, mounts an interactive uPlot chart into a live DOM element from a plain spec (mountPlot); uPlot is an optional peer dependency, so the dependency-free core is never affected.

@mcmcjs/plots: the data-builder / renderer split

@mcmcjs/plots builds MCMC diagnostics on top of the engine, split into two layers:

  • Data builders. Each *Data function turns a Samples set into a plain, serializable object: the numbers a plot needs, with no rendering. This is what mcmc plot --json emits.
  • Renderers. Each renderer turns that object into one backend’s output: render*Terminal (braille/ASCII via @mcmcjs/charts), render*SVG (standalone vector), and the HTML path.

buildHtmlDocument emits one self-contained, offline HTML page with uPlot inlined for the interactive charts (pan, zoom, PNG/SVG export); forest, pair, and the table and grid kinds embed their SVG. Because the builders are serializable and dependency-free, the same data drives every backend, and a consumer can build the data once and render it anywhere.

@mcmcjs/plots-gl: the WebGL layer

Three kinds have interactive WebGL renderers: a 3D point cloud (scatter3d), a scatter-plot matrix (splom), and parallel coordinates (parallel-coords). They are browser-only and backed by regl, an optional peer dependency.

Their data builders (scatter3dData, splomData, parallelCoordsData) live in the dependency-free @mcmcjs/plots package; only the interactive renderers live here. That separation is the point: the terminal, SVG, and HTML backends never pull in WebGL, and the WebGL renderers load regl on demand. Each mount function returns a handle for updating and teardown, mirroring @mcmcjs/charts/dom.