SVGのテキスト折り返し：tspanで計測済みの行を作る

<!doctype html>
<html lang="en">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Measured SVG label lines</title>
<style>
  body { margin: 24px; font: 16px system-ui; background: #f6f2e8; }
  #cases { display: grid; grid-template-columns: repeat(2, 360px); gap: 20px; }
  figure { margin: 0; }
  svg { display: block; background: white; }
  figcaption { margin: 6px 0; }
  pre { white-space: pre-wrap; font-size: 12px; }
</style>
<h1>Keep artwork and label layout separate</h1>
<div id="cases"></div>
<pre id="report"></pre>
<script>
  const ns = 'http://www.w3.org/2000/svg';
  const emblem = 'M60 32 L100 72 L60 112 L20 72 Z M60 54 L78 72 L60 90 L42 72 Z';
  function element(name, attributes) {
    const node = document.createElementNS(ns, name);
    for (const [key, value] of Object.entries(attributes)) node.setAttribute(key, value);
    return node;
  }
  function wrapWords(text, source, { width, maxLines, lineHeight }) {
    text.replaceChildren();
    if (!(width > 0 && lineHeight > 0 && Number.isInteger(maxLines) && maxLines > 0)) {
      return { status: 'invalid-options', lines: [] };
    }
    const words = source.trim().split(/\s+/u).filter(Boolean);
    const probe = text.cloneNode(false);
    probe.setAttribute('visibility', 'hidden');
    text.parentNode.append(probe);
    const measure = value => { probe.textContent = value; return probe.getComputedTextLength(); };
    const lines = [];
    let line = '';
    try {
      for (const word of words) {
        const wordWidth = measure(word);
        if (wordWidth > width) {
          return { status: 'overlong-word', word, measuredWidth: wordWidth, lines: [] };
        }
        const candidate = line ? line + ' ' + word : word;
        if (line && measure(candidate) > width) {
          lines.push(line);
          line = word;
        } else line = candidate;
      }
      if (line) lines.push(line);
      if (lines.length > maxLines) {
        return { status: 'too-many-lines', requiredLines: lines.length, lines: [] };
      }
      const x = text.getAttribute('x');
      lines.forEach((value, index) => {
        const span = element('tspan', { x, dy: index ? lineHeight : 0 });
        span.textContent = value;
        text.append(span);
      });
      return { status: 'ok', lines,
        lengths: [...text.children].map(span => span.getComputedTextLength()) };
    } finally { probe.remove(); }
  }
  const cases = [
    { id: 'normal', source: 'Keep artwork and labels separate', width: 200, maxLines: 4 },
    { id: 'narrow', source: 'Keep artwork and labels separate', width: 110, maxLines: 5 },
    { id: 'changed', source: 'Keep the original artwork beside every exported label', width: 200, maxLines: 4 },
    { id: 'long-word', source: 'Artwork supercalifragilisticexpialidocious', width: 110, maxLines: 5 },
    { id: 'line-limit', source: 'Keep artwork and labels separate', width: 110, maxLines: 2 },
    { id: 'literal', source: 'Cove <g> & field', width: 200, maxLines: 4 },
  ];
  const entries = cases.map(test => {
    const figure = document.createElement('figure');
    const svg = element('svg', { width: 360, height: 240, viewBox: '0 0 360 240' });
    svg.append(element('path', { d: emblem, fill: '#176b5b', 'fill-rule': 'evenodd' }));
    svg.append(element('rect', { x: 140, y: 34, width: test.width, height: 170,
      fill: 'none', stroke: '#ce7b55', 'stroke-dasharray': '4 4' }));
    const text = element('text', { x: 140, y: 60, 'font-family': 'Arial, sans-serif',
      'font-size': 22, fill: '#172b34' });
    svg.append(text);
    const caption = document.createElement('figcaption');
    figure.append(svg, caption);
    document.getElementById('cases').append(figure);
    return { test, svg, text, caption };
  });
  async function run() {
    await document.fonts.ready;
    const results = entries.map(({ test, svg, text, caption }) => {
      const result = wrapWords(text, test.source, { ...test, lineHeight: 30 });
      caption.textContent = test.id + ': ' + result.status;
      return { ...test, ...result, fontFamily: getComputedStyle(text).fontFamily,
        fontSize: getComputedStyle(text).fontSize, tspanCount: text.children.length,
        pathD: svg.querySelector('path').getAttribute('d'),
        pathCount: svg.querySelectorAll('path').length,
        imageCount: svg.querySelectorAll('image').length,
        foreignObjectCount: svg.querySelectorAll('foreignObject').length,
        serialized: new XMLSerializer().serializeToString(svg) };
    });
    document.getElementById('report').textContent = JSON.stringify({
      fontStatus: document.fonts.status, policy: 'Whitespace words; reject a long word or too many lines without partial output', results,
    }, null, 2);
  }
  run();
</script>
</html>