Visualising results

kestrel-chartkit is a calculation library. What it returns — indicator values, extras, alerts, regimes, scores, zones — is plain data. Drawing it is the job of a renderer, and there are two that fit the crate:

Renderer	What you get	Status
chartlet	Static, accessible SVG or HTML from a JSON specification, rendered at build time (CLI, Rust crate or npm package)	usable, pre-1.0
kestrel-loom	Interactive candlestick chart in the browser: Rust → WebAssembly → Canvas 2D, with indicator panes and drawing tools	alpha, in development

Both are in development, like this crate. Expect their interfaces to change.

Static charts with chartlet

Every chart on this site is a chartlet specification written by examples/site_showcase.rs: the example streams bars through the indicators, collects what they return, and writes the numbers into a "type": "time" specification — candles as an ohlc layer, indicator values as line layers in the price pane or a pane of their own, zones as band, levels and alerts as annotation. chartlet then renders it when the site is built. The showcase shows the result for every indicator.

let mut rsi = build_checked("rsi", &HashMap::new())?;
let mut points = Vec::new();
for bar in &bars {
    if let Some(output) = rsi.on_bar(bar) {
        points.push(format!(r#"{{"time":{},"value":{:.2}}}"#, bar.timestamp, output.value));
    }
}
let spec = format!(
    r#"{{"schemaVersion":1,"type":"time","title":"RSI 14","panes":[{{"layers":[{{"mark":"line","name":"RSI","points":[{}]}}]}}]}}"#,
    points.join(",")
);
// chartlet render spec.json --format svg, or chartlet::render_json from Rust

A few things decide whether a chart reads well:

• Put a line where its values live. output_unit(name) says whether value is a price; the extras do not have a declared unit yet, so check their range before drawing them over candles.
• Leave gaps as gaps. A field that is missing on some bars (a zone that ended, a pivot not yet confirmed) is null in the specification, so the line breaks instead of bridging the gap.
• Mind the limits. chartlet draws at most four panes, six data layers and six annotations per pane; it reports overlapping labels and dense candles as warnings.

Interactive charts with kestrel-loom

kestrel-loom renders in the browser and takes its indicator math from this crate. Overlays that belong to a chart rather than to an indicator — signal markers, levels, zones — travel as a viz::scene::Scene: a renderer-neutral model of panes, axes and objects (Polyline, BoundedBox, Fill, Text, Tooltip, Table), each with an id so a live chart can replace one object per tick (Pane::upsert_object). The scene types are plain data, serialisable with the default serde feature.

The built-in quick-look renderers

The crate still contains two small SVG renderers, viz::render_chart_svg (candles, lines, zones, markers) and viz::render_scene_svg (a Scene as SVG). They are meant for a quick look in tests and debugging, not as a presentation layer: no axes labels to speak of, no accessibility, no responsive layout. Colours pass through sanitize_color (#rgb, #rrggbb, #rrggbbaa or var(--name); anything else becomes #29b6f6). For anything a reader should see, use chartlet or kestrel-loom.