SVGのfeComposite：in、out、xorの結果を比較する

<!doctype html>
<html lang="en">
<meta charset="utf-8">
<title>Original SVG composite artwork</title>
<style>
  body { margin: 24px; font: 16px system-ui; background: #f6f2e8; }
  main { display: grid; grid-template-columns: repeat(3, 260px); gap: 18px; }
  figure { margin: 0; }
  svg { display: block; background: white; border: 1px solid #bbb; }
  figcaption { margin: 6px 0; }
  pre { white-space: pre-wrap; font-size: 12px; }
</style>
<h1>Original operands and rendered composites</h1>
<main id="cases"></main>
<pre id="report"></pre>
<script>
  const A = 'M24 24 H132 V56 H192 V136 H24 Z';
  const B = 'M92 8 L216 84 L92 152 L60 84 Z';
  const svgNS = 'http://www.w3.org/2000/svg';
  const cases = [
    { id: 'a' }, { id: 'b' },
    { id: 'a-in-b', operator: 'in' },
    { id: 'a-out-b', operator: 'out' },
    { id: 'a-xor-b', operator: 'xor' },
    { id: 'b-in-a', operator: 'in', reverse: true },
    { id: 'b-out-a', operator: 'out', reverse: true },
    { id: 'b-xor-a', operator: 'xor', reverse: true },
    { id: 'a-out-half-b', operator: 'out', opacity: 0.5 },
  ];
  function documentSVG(test, width) {
    const height = width * 2 / 3;
    const id = test.id + '-' + width;
    const second = '<svg xmlns="' + svgNS + '" width="240" height="160" viewBox="0 0 240 160">'
      + '<path d="' + B + '" fill="#d4a53a" opacity="' + (test.opacity ?? 1) + '"/></svg>';
    const href = 'data:image/svg+xml;charset=utf-8,' + encodeURIComponent(second);
    const first = test.reverse ? 'operandB' : 'SourceGraphic';
    const other = test.reverse ? 'SourceGraphic' : 'operandB';
    const defs = test.operator ? '<defs><filter id="' + id + '" filterUnits="userSpaceOnUse" primitiveUnits="userSpaceOnUse" x="0" y="0" width="240" height="160" color-interpolation-filters="sRGB">'
      + '<feImage href="' + href + '" x="0" y="0" width="240" height="160" preserveAspectRatio="none" result="operandB"/>'
      + '<feComposite in="' + first + '" in2="' + other + '" operator="' + test.operator + '"/></filter></defs>' : '';
    return '<svg xmlns="' + svgNS + '" width="' + width + '" height="' + height + '" viewBox="0 0 240 160">'
      + defs + '<path d="' + (test.id === 'b' ? B : A) + '" fill="' + (test.id === 'b' ? '#d4a53a' : '#176b5b')
      + '"' + (test.operator ? ' filter="url(#' + id + ')"' : '') + '/></svg>';
  }
  async function run() {
    const results = [];
    for (const width of [120, 240]) {
      for (const test of cases) {
        const source = documentSVG(test, width);
        const svg = new DOMParser().parseFromString(source, 'image/svg+xml').documentElement;
        const figure = document.createElement('figure');
        const caption = document.createElement('figcaption');
        caption.textContent = test.id + ', ' + width + ' × ' + width * 2 / 3;
        figure.append(document.importNode(svg, true), caption);
        document.getElementById('cases').append(figure);
        const path = figure.querySelector('path');
        const bbox = path.getBBox();
        const image = new Image();
        image.src = 'data:image/svg+xml;charset=utf-8,' + encodeURIComponent(source);
        await image.decode();
        const canvas = document.createElement('canvas');
        canvas.width = width;
        canvas.height = width * 2 / 3;
        const ctx = canvas.getContext('2d');
        ctx.drawImage(image, 0, 0);
        const sample = (x, y) => [...ctx.getImageData(Math.floor(x * width / 240), Math.floor(y * width / 240), 1, 1).data];
        const hash = [...new Uint8Array(await crypto.subtle.digest('SHA-256', new TextEncoder().encode(path.getAttribute('d'))))]
          .map(v => v.toString(16).padStart(2, '0')).join('');
        const download = document.createElement('a');
        download.href = image.src;
        download.download = test.id + '-' + width + '.svg';
        download.textContent = 'Save SVG';
        figure.append(download);
        results.push({ id: test.id, width, height: canvas.height, d: path.getAttribute('d'), dSHA256: hash,
          bbox: { x: bbox.x, y: bbox.y, width: bbox.width, height: bbox.height },
          directPaths: svg.querySelectorAll('path').length, filterImages: svg.querySelectorAll('feImage').length,
          aOnly: sample(40, 40), bOnly: sample(200, 84), overlap: sample(120, 84), outside: sample(230, 150) });
      }
    }
    document.getElementById('report').textContent = JSON.stringify({ A, B, results }, null, 2);
  }
  run();
</script>
</html>