BeeswarmForce.html.svelte component

<!--
  @component
  Generates an HTML Beeswarm chart using a [d3-force simulation](https://github.com/d3/d3-force).
 -->
<script>
  import { getContext, untrack } from 'svelte';
  import { forceSimulation, forceX, forceY, forceCollide } from 'd3-force';

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

  /**
   * @typedef {Object} Props
   * @property {number} [r=4] - The circle radius size in pixels.
   * @property {number} [strokeWidth=0.5] - The circle's stroke width in pixels.
   * @property {string} [stroke='#fff'] - The circle's stroke color.
   * @property {number} [xStrength=0.95] - The value passed into the `.strength` method on `forceX`, which is used as the `'x'` property on the simulation. See [the documentation](https://github.com/d3/d3-force#x_strength) for more.
   * @property {number} [yStrength=0.075] - The value passed into the `.strength` method on `forceY`, which is used as the `'y'` property on the simulation. See [the documentation](https://github.com/d3/d3-force#y_strength) for more.
   * @property {Function} [getTitle] - An accessor function to get the field on the data element to display as a hover label. Mostly useful for debugging, needs better styling for production.
   */

  /** @type {Props} */
  let {
    r = 4,
    strokeWidth = 0.5,
    stroke = '#fff',
    xStrength = 0.95,
    yStrength = 0.075,
    getTitle
  } = $props();

  /** @type {any[]} */
  let nodes = $state([]);

  let simulation = $derived.by(() => {
    if (!$width || !$height || !$data.length) return null;

    const sim = forceSimulation($data.map((/** @type {any} */ d) => ({ ...d })))
      .force(
        'x',
        forceX()
          .x(d => $xGet(d))
          .strength(xStrength)
      )
      .force(
        'y',
        forceY()
          .y($height / 2)
          .strength(yStrength)
      )
      .force('collide', forceCollide(r))
      .stop();

    return sim;
  });

  $effect(() => {
    if (!simulation) {
      nodes = [];
      return;
    }

    untrack(() => {
      // Run the simulation for a fixed number of iterations
      const maxIterations = Math.ceil(
        Math.log(simulation.alphaMin()) / Math.log(1 - simulation.alphaDecay())
      );

      for (let i = 0; i < maxIterations; ++i) {
        simulation.tick();
      }

      // Update nodes state to trigger reactivity
      nodes = [...simulation.nodes()];
    });
  });
</script>

<div class="bee-group">
  {#each nodes as node}
    <div
      class="bee"
      style="
        left:{node.x}px;
        top: {node.y}px;
        width: {r * 2}px;
        height: {r * 2}px;
        background: {$zGet(node)};
        border-width: {strokeWidth}px;
        border-color: {stroke};
        "
    >
      {#if getTitle}
        <div class="title">{getTitle(node)}</div>
      {/if}
    </div>
  {/each}
</div>

<style>
  .bee {
    position: absolute;
    border-style: solid;
    border-radius: 50%;
    transform: translate(-50%, -50%);
  }
  .title {
    display: none;
    white-space: nowrap;
    padding: 0 3px;
    border-radius: 3px;
    font-size: 12px;
    pointer-events: none;
    position: absolute;
    top: -15px;
    left: 5px;
    z-index: 9999;
  }
  .bee:hover .title {
    display: block;
  }
</style>