Crop to a shape

<div class="demo demo--wide">
  <input id="photo" name="photo" type="file">
  <div class="demo-row">
    <button class="demo-btn" id="take">Take the file</button>
    <button class="demo-btn demo-btn--ghost" id="sample">Use a test card</button>
  </div>
  <div class="result" id="result" hidden>
    <img id="out" alt="The cropped picture">
    <dl class="demo-kv" id="facts"></dl>
  </div>
  <p class="demo-hint">The test card has four known quarters, so you can see that what comes out is
    exactly what you selected — at the original's resolution, not the screen's.</p>
</div>

import { createImageCropper } from 'https://devix.pk/cdn/oss/image-cropper@1.0.0/index.js';

const result = document.getElementById('result');
const out = document.getElementById('out');
const facts = document.getElementById('facts');

const picker = createImageCropper(document.getElementById('photo'), {
  aspect: null,
  aspects: [
    { label: 'Free', value: null },
    { label: '1:1', value: 1 },
    { label: '4:3', value: 4 / 3 },
    { label: '16:9', value: 16 / 9 },
    { label: '2:3', value: 2 / 3 },
  ],
  preview: true,
  maxWidth: 1200,
  onChange: (crop) => {
    if (!crop) return;
    facts.innerHTML = `<div><dt>crop</dt><dd>${crop.width} × ${crop.height}</dd></div>
      <div><dt>at</dt><dd>${crop.x}, ${crop.y}</dd></div>`;
    result.hidden = false;
    out.removeAttribute('src');
  },
});

document.getElementById('take').addEventListener('click', async () => {
  const crop = picker.getCrop();
  if (!crop) return;
  const file = await picker.toFile('cropped', { type: 'image/png' });
  out.src = URL.createObjectURL(file);
  facts.innerHTML = `<div><dt>file</dt><dd>${file.name}</dd></div>
    <div><dt>size</dt><dd>${(file.size / 1024).toFixed(1)} kB</dd></div>
    <div><dt>crop</dt><dd>${crop.width} × ${crop.height}</dd></div>
    <div><dt>from</dt><dd>${crop.x}, ${crop.y}</dd></div>`;
  result.hidden = false;
});

document.getElementById('sample').addEventListener('click', async () => {
  const canvas = Object.assign(document.createElement('canvas'), { width: 960, height: 540 });
  const ctx = canvas.getContext('2d');
  const quarters = [['#ef4444', 0, 0], ['#22c55e', 480, 0], ['#3b82f6', 480, 270], ['#eab308', 0, 270]];
  for (const [colour, x, y] of quarters) {
    ctx.fillStyle = colour;
    ctx.fillRect(x, y, 480, 270);
  }
  ctx.strokeStyle = 'rgba(255,255,255,.7)';
  ctx.lineWidth = 2;
  for (let x = 0; x <= 960; x += 120) { ctx.beginPath(); ctx.moveTo(x, 0); ctx.lineTo(x, 540); ctx.stroke(); }
  for (let y = 0; y <= 540; y += 120) { ctx.beginPath(); ctx.moveTo(0, y); ctx.lineTo(960, y); ctx.stroke(); }
  ctx.fillStyle = '#fff';
  ctx.font = 'bold 40px system-ui';
  ctx.textAlign = 'center';
  ctx.fillText('960 × 540', 480, 290);

  const blob = await new Promise((r) => canvas.toBlob(r, 'image/png'));
  await picker.open(new File([blob], 'test-card.png', { type: 'image/png' }));
});

@import url('https://devix.pk/cdn/oss/image-cropper@1.0.0/image-cropper.min.css');

.result { display: flex; align-items: flex-start; gap: 16px; }
.result[hidden] { display: none; }
#out { max-width: 140px; max-height: 110px; border-radius: 8px; }
#facts { flex: 1; }