MapPoints.canvas.svelte component

<!--
  @component
  Generates canvas dots onto a map using [d3-geo](https://github.com/d3/d3-geo).
 -->
<script>
  import { getContext, onMount, untrack } from 'svelte';
  import { scaleCanvas } from 'layercake';

  const { data, width, height } = getContext('LayerCake');

  const { ctx } = getContext('canvas');

  /**
   * @typedef {Object} Props
   * @property {Function} projection - A D3 projection function. Pass this in as an uncalled function, e.g. `projection={geoAlbersUsa}`.
   * @property {number} [r=3.5] - The point's radius.
   * @property {string} [fill='yellow'] - The point's fill color.
   * @property {string} [stroke='#000'] - The point's stroke color.
   * @property {number} [strokeWidth=1] - The point's stroke width.
   * @property {Array<Object>|undefined} [features] - A list of GeoJSON features to plot. If unset, the plotted features will defaults to those in `$data.features`, assuming this field a list of GeoJSON features.
   */

  /** @type {Props} */
  let {
    projection,
    r = 3.5,
    fill = 'yellow',
    stroke = '#000',
    strokeWidth = 1,
    features
  } = $props();

  let projectionFn = $derived(projection().fitSize([$width, $height], $data));

  let featuresToDraw = $derived(features || $data.features);
  onMount(() => {
    $effect(() => {
      if ($width && $height) {
        untrack(() => {
          if (!$ctx) return;

          scaleCanvas($ctx, $width, $height);
          $ctx.clearRect(0, 0, $width, $height);

          // To scale the circle by size, set width and height to `$rGet(d.properties)`
          featuresToDraw.forEach(
            /** @param {any} d */ d => {
              $ctx.beginPath();
              const coordinates = projectionFn(d.geometry.coordinates);
              $ctx.arc(coordinates[0], coordinates[1], r, 0, 2 * Math.PI, false);
              $ctx.fillStyle = fill;
              $ctx.fill();
              $ctx.lineWidth = strokeWidth;
              $ctx.strokeStyle = stroke;
              $ctx.stroke();
            }
          );
        });
      }
    });
  });
</script>