lodviz_core

Core visualization primitives and data structures for lodviz-rs — a pure-Rust, SVG-based data visualization library.

Features

• Tidy Data Model — DataTable, DataRow, and FieldValue for heterogeneous, column-oriented data
• Grammar of Graphics — Declarative Encoding and Field types inspired by Vega-Lite
• Scales — LinearScale, BandScale, and OrdinalScale for mapping data domains to screen ranges
• LTTB Downsampling — Largest-Triangle-Three-Buckets algorithm for visually-preserving time-series reduction
• M4 Downsampling — Fast Min-Max-Min-Max algorithm for large OHLC/financial datasets
• Statistical Algorithms — KDE, box-plot stats, mean, median, percentiles
• ColorMap — Perceptually uniform color interpolation via Oklab; sequential palettes (Viridis, Plasma, Inferno, Magma, Cividis, Turbo, Grayscale) and diverging palettes (RdBu, PuOr, PiYG, BrBG)
• Beeswarm Layout — Deterministic jitter / greedy beeswarm placement for strip charts
• Sankey Layout — BFS column assignment + proportional node heights + cubic Bézier ribbons
• Chord Layout — Arc angles from flow totals + quadratic Bézier ribbon paths
• Contour Extraction — Marching squares iso-lines and iso-bands from 2-D scalar grids
• Theming — ChartConfig and palette definitions reused across renderers
• Accessibility — A11y primitives for screen-reader friendly SVG output
• WASM-compatible — Pure logic, no OS runtime dependencies

Installation

[dependencies]
lodviz_core = "0.2"

Usage

Working with data

use lodviz_core::core::data::{DataPoint, Series, Dataset};

let series = Series {
    label: "Temperature".to_string(),
    points: (0..100)
        .map(|i| DataPoint::new(i as f64, (i as f64 * 0.1).sin() * 20.0 + 15.0))
        .collect(),
    color: None,
};

let dataset = Dataset { series: vec![series] };

LTTB downsampling

Reduce 10,000 points to 300 while preserving the visual shape:

use lodviz_core::core::data::DataPoint;
use lodviz_core::algorithms::lttb::lttb_downsample;

let data: Vec<DataPoint> = (0..10_000)
    .map(|i| DataPoint::new(i as f64, (i as f64 * 0.01).sin()))
    .collect();

let reduced = lttb_downsample(&data, 300);
assert_eq!(reduced.len(), 300);

Scales

use lodviz_core::core::scale::LinearScale;

let scale = LinearScale::new(0.0, 100.0, 0.0, 600.0);
let px = scale.map(50.0); // → 300.0

Encoding specification

use lodviz_core::core::encoding::{Encoding, Field};

let enc = Encoding::new()
    .x(Field::quantitative("timestamp"))
    .y(Field::quantitative("value"))
    .color(Field::nominal("series"));

Data Pipeline

lodviz_core accepts data at three levels of abstraction, from lowest to highest:

[1] Vec<DataPoint>          ← raw Rust types, no parsing needed
[2] DataTable / DataRow     ← tidy model, heterogeneous columns
[3] parse_csv(&str)         ← CSV text → DataTable

Level 1 — Raw Rust types

The native input type for charts is Vec<DataPoint> (x/y as f64), grouped into Series<DataPoint> and then Dataset. No parsing, no extra allocation — construct data directly.

use lodviz_core::core::data::{DataPoint, Dataset, Series};

let series = Series::new(
    "Revenue",
    (0..12).map(|i| DataPoint::new(i as f64, revenue[i])).collect(),
);
let dataset = Dataset::from_series(series);

Dedicated types exist for specialised chart kinds:

Level 2 — Tidy Data Model

When your data has heterogeneous columns (numbers, text, timestamps mixed), use DataTable. Each row is a DataRow (HashMap<String, FieldValue>).

use lodviz_core::core::field_value::{DataTable, DataRow, FieldValue};
use lodviz_core::core::encoding::{Encoding, Field};

// Manual construction
let mut row: DataRow = DataRow::new();
row.insert("month".into(), FieldValue::Numeric(1.0));
row.insert("value".into(), FieldValue::Numeric(420.0));
row.insert("region".into(), FieldValue::Text("North".into()));
let table = DataTable::from_rows(vec![row]);

// Define the encoding: which column maps to which axis / color channel
let enc = Encoding::new(
    Field::quantitative("month"),
    Field::quantitative("value"),
).with_color(Field::nominal("region"));

// Convert to a chart-ready Dataset (auto group-by "region")
let dataset = table.to_dataset(&enc);

FieldValue supports implicit conversion from primitive Rust types:

let v: FieldValue = 3.14_f64.into();   // Numeric
let v: FieldValue = "East".into();     // Text
let v: FieldValue = true.into();       // Bool

Level 3 — CSV parser

To load CSV (e.g. from an HTTP fetch in the browser), use parse_csv:

use lodviz_core::core::csv::parse_csv;

let csv = "\
month,value,region
1,420,North
2,380,South
3,510,North";

let table = parse_csv(csv)?;
// → same DataTable as Level 2, then apply encoding as above

Parser rules:

• First non-empty, non-comment (#) line → header
• Numeric cells → FieldValue::Numeric(f64)
• Non-numeric cells → FieldValue::Text
• Missing cells → FieldValue::Null

Note: the parser accepts &str. HTTP fetching and file I/O are the responsibility of the application — this crate contains no I/O.

Full pipeline

CSV &str
  ──parse_csv()──▶ DataTable
                      ──to_dataset(&enc)──▶ Dataset
                                                ──lttb_downsample(n)──▶ Dataset (LOD)
                                                                             ──▶ SVG (lodviz_components)

Algorithm References

• LTTB: Sveinn Steinarsson (2013) — Downsampling Time Series for Visual Representation (PDF)
• M4: Uwe Jugel et al. (2014) — M4: A Visualization-Oriented Time Series Data Aggregation
• Oklab: Björn Ottosson (2020) — A perceptual color space for image processing (blog)
• Marching Squares: Lorensen & Cline (1987) — classic iso-contour extraction via 2×2 cell case table

License

MIT — see LICENSE