Weighted chord charts

AddChord renders directed flows as proportional endpoint slots, node arcs, and curved ribbons. SVG and PNG use one prepared native scene. Static exports are deterministic and script-free.

var chart = Chart.Create().AddChord("Transfers", new[] {
    new ChartNode("north", "Support"), new ChartNode("south", "Support"),
    new ChartNode("central", "Central")
}, new[] {
    new ChartFlowLink("north-south", "north", "south", 18),
    new ChartFlowLink("south-north", "south", "north", 7),
    new ChartFlowLink("priority", "north", "south", 4),
    new ChartFlowLink("internal", "central", "central", 3),
    new ChartFlowLink("none", "central", "north", 0)
}).ConfigureChord(options => {
    options.StartAngleDegrees = -120;
    options.SweepAngleDegrees = 300;
    options.NodeGapDegrees = 5;
    options.NodeThicknessRatio = .09;
    options.RibbonOpacity = .45;
    options.DirectionCue = ChartChordDirectionCue.TargetChevron;
    options.LabelContent = ChartChordLabelContent.LabelAndTotals;
});
chart.Series[0].WithNodeState("north", ChartSeriesState.Warning);

Each node has an explicit ID and display label. Labels may repeat. Flow IDs remain distinct for parallel and reciprocal links; the renderer does not aggregate them. Cycles and self flows are accepted. A self flow occupies separate outgoing and incoming slots on its own node. Incoming, outgoing, and their combined endpoint totals must remain finite. Invalid identities, references, or aggregates fail before a series is added.

The node arc represents incoming plus outgoing weight, so each flow contributes to two endpoint slots. Authored node order determines clockwise arc order. Outgoing slots come before incoming slots on each arc; flows retain authored order within both sets. No crossing minimizer or automatic reordering runs. The global angular allocation divides by a finite node reference before summing, preserving proportional geometry for subnormal weights and independent huge flows without requiring a finite global raw total.

Flow values are finite and non-negative. Zero flows and nodes without positive endpoints retain source identities and raw values but draw no filled ribbon or arc. Empty and all-zero inputs emit chord.no-positive-flow. Positive weights or node thickness that collapse in native geometry emit chord.precision-collapse; they receive no minimum-width substitute. Increasing canvas size cannot recover a ratio that underflows the numeric angular allocation.

ChartOptions.Chord holds the mutable options configured by ConfigureChord:

Defaults are a full circle starting at -90 degrees, a 3-degree node gap, 0.06 node thickness, 0.35 ribbon opacity, target chevrons, and labels with combined values. Labels use shared measured fitting outside the circle. Compact output may shorten or omit a label and emits chord.label-overflow; full labels and raw totals remain available in node semantics. ChartSeries.ShowDataLabels = false hides visible labels.

ChartSeries.WithNodeState(id, state) scopes semantic styling to that series. NodeStates is read-only. Existing point color, fill-pattern, label, and label-style APIs refer to authored node ordinals. Ribbons inherit the source node's color, pattern and semantic state. WithFlowStyle(id, new ChartFlowStyle(...)) overrides one authored flow's fill, opacity, pattern or outline; WithFlowState(id, state) overrides its semantic state. Explicit colors take precedence over semantic fills. Null removes either flow override; an explicit state of None suppresses inheritance. See shared flow paint conventions for precedence and outline defaults. Prepared exports keep their geometry, styles, formatting, and semantics after the mutable model changes.

Node and link groups publish data-cfx-target-kind, data-cfx-target-id, authored source indexes, and data-cfx-coordinate-system="polar". Links retain the actual source/target IDs and labels, raw data-cfx-value, both endpoint angles, and direction. Node groups retain raw incoming/outgoing totals and arc geometry. Scale metadata is data-cfx-weight-reference and data-cfx-normalized-angular-scale: divide a raw weight by the reference before applying the angular scale. There are no invented Cartesian point or sourcePoint ordinals.

The HTML adapter consumes these same targets for selection and tooltips. Chart markup's numeric grammar does not support typed relationships; author chord charts through the C# API. Custom ordering strategies and an independent quantitative color dimension remain outside the current chord options.