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Changelog

Source: NEWS.md

vellum (development version)

vellum 0.2.0

  • Breaking: renamed the grid-colliding exports to a vl_ prefix so attaching vellum no longer masks grid: gpar() → vl_gpar(), unit() → vl_unit(), viewport() → vl_viewport(), arrow() → vl_arrow(), and pattern() → vl_pattern(). The old names are removed (no aliases).

  • Multi-line and per-datum rich text. text_grob() labels may now contain embedded newlines (\n), stacked baseline-to-baseline; md() gained the same and is now vectorised — md(x) returns a single label for a length-1 x or a list of labels for a vector, so a label grob can carry one distinct rich label per position. Single-line, single-label output is byte-for-byte unchanged. (Rust is untouched — shaping stays R-side.)

  • Accessibility (a11y). vl_scene(title=, desc=) and the new describe() setter attach an accessible name and long description (alt text) to a scene. When set:

    • the SVG backend marks the root <svg role="img" aria-labelledby=…> and emits <title>/<desc> (WCAG 1.1.1);
    • the PDF backend produces a tagged PDF — the chart is a Figure in the structure tree carrying the description as Alt text. Purely additive: a scene with no title/desc renders byte-for-byte as before. (Strict PDF/UA-1 validation is a planned follow-up; the tag tree + Alt ship now.)

  • datashade(weight=) now recycles a scalar and errors on a wrong-length vector, instead of silently discarding a mismatched weight and reverting to a plain count.

vellum 0.1.1

  • Compound native + mm / npc + mm units. A position unit combined with an absolute unit now forms a compound unit — a data/panel anchor plus an exact absolute offset — instead of erroring. unit(1, "native") + unit(2, "mm") resolves to the native position shifted by exactly 2 mm at render, at any scale or aspect (the offset is applied device-side after the base resolves). This is the deferred “B1” route; it unlocks device-exact label nudges, halos, and drop-shadow offsets in the grammar layer. Mixing two different position bases (e.g. npc and native) still errors. Unit arithmetic scales the base and the offset together. Additive change: a scene using no compound units renders byte-for-byte as before.

vellum 0.1.0

First release. vellum is a low-level graphics framework for R in the spirit of grid, with a Rust backend: you describe a scene through a small declarative R API, and the scene graph, unit/layout engine, and rendering all run in Rust.

Scenes and rendering

  • Build a scene functionally with vl_scene() and a pipeline of push(), draw(), and pop() over an immutable tree.
  • render() draws the same scene to PNG, SVG, or PDF, picking the backend from the file extension — raster via tiny-skia, PDF via krilla, SVG hand-rolled. Output is byte-stable and snapshot-testable.
  • display() draws a scene into the active graphics device; scene_raster() / scene_svg() return the rendered scene in memory.

Grobs, units, and layout

  • Vectorised drawing primitives (rect, circle, points, segments, lines, path, polygon, text, raster, …) that batch internally.
  • A unit system (unit(), grobwidth, …) and nested viewport()s with their own scales, rotation, and arbitrary-path clipping, plus a row/column layout solver with "null" (flexible) tracks.

Paint model

  • A modern paint model shared across all backends: linear and radial gradients, tiling patterns, alpha/luminance masks, group opacity (viewport(alpha =)), reusable style()s, and hand-drawn sketch() rendering.

Text

  • Device-independent shaping and measurement through textshaping / systemfonts — the same stack as ragg/svglite — with per-glyph fallback, justification, and rotation, plus Markdown-style rich labels via md().

Big data

  • datashade() aggregates millions of points into a density raster in a single pass — cost scales with output pixels, not point count — with no overplotting and small output files.

Retained scene graph

  • Because the scene is retained rather than drawn-and-forgotten, it can be queried and edited: node_names() / get_node() / edit_node(), hit_test() to pick the topmost grob under a point, and scene_model() to serialize a per-element model (data keys, bounding boxes) — the foundation the vellumplot grammar and the vellumwidget widget layer build on.

Interop

  • as_vellum() / render_grid() render an existing grid grob tree — including ggplot2 and lattice — through the vellum backend.

Under the hood

  • The R package wires to a Rust crate via extendr; crates are vendored for offline/CRAN builds.