Radar.svelte component

<!--
  @component
  Generates an SVG radar chart. Each row becomes one polygon. The x accessor must be a list of keys, one per axis, and the x scale maps each value to a radius.
 -->
<script>
  import { line, curveCardinalClosed } from 'd3-shape';
  import { getLayerCakeContext } from 'layercake';

  const k = getLayerCakeContext();

  /**
   * @typedef {Object} Props
   * @property {string} [fill='#f0c'] - The polygon's fill color.
   * @property {string} [stroke='#f0c'] - The polygon's stroke color.
   * @property {number} [strokeWidth=2] - The polygon's stroke width in pixels.
   * @property {number} [fillOpacity=0.5] - The polygon's fill opacity.
   * @property {number} [r=4.5] - Each circle's radius in pixels.
   * @property {string} [circleFill='#f0c'] - Each circle's fill color.
   * @property {string} [circleStroke='#fff'] - Each circle's stroke color.
   * @property {number} [circleStrokeWidth=1] - Each circle's stroke width in pixels.
   */

  /** @type {Props} */
  let {
    fill = '#f0c',
    stroke = '#f0c',
    strokeWidth = 2,
    fillOpacity = 0.5,
    r = 4.5,
    circleFill = '#f0c',
    circleStroke = '#fff',
    circleStrokeWidth = 1
  } = $props();

  let angleSlice = $derived((Math.PI * 2) / k.config.x.length);

  // Each value is a radius. Axis i sits at angle i around the circle, starting from the top.
  let path = $derived(
    line(
      (/** @type {number} */ d, i) => d * Math.cos(angleSlice * i - Math.PI / 2),
      (/** @type {number} */ d, i) => d * Math.sin(angleSlice * i - Math.PI / 2)
    ).curve(curveCardinalClosed)
  );
</script>

<g transform="translate({k.width / 2}, {k.height / 2})">
  {#each k.data as row}
    {@const xVals = k.xGet(row)}
    <!-- Draw a line connecting all the dots -->
    <path
      class="path-line"
      d={path(xVals)}
      {stroke}
      stroke-width={strokeWidth}
      {fill}
      fill-opacity={fillOpacity}
    ></path>

    <!-- One dot per value -->
    {#each xVals as circleR, i}
      {@const thisAngleSlice = angleSlice * i - Math.PI / 2}
      <circle
        cx={circleR * Math.cos(thisAngleSlice)}
        cy={circleR * Math.sin(thisAngleSlice)}
        {r}
        fill={circleFill}
        stroke={circleStroke}
        stroke-width={circleStrokeWidth}
      ></circle>
    {/each}
  {/each}
</g>

<style>
  .path-line {
    stroke-linejoin: round;
    stroke-linecap: round;
  }
</style>