https://n69.in/blog/canvas/ Recent content in Canvas on Rustam Garifulin Hugo en-US Copyright © 2025, Rustam Garifulin. Mon, 20 Apr 2026 00:00:00 +0000 https://n69.in/blog/fractional-indexing/ Mon, 20 Apr 2026 00:00:00 +0000 https://n69.in/blog/fractional-indexing/ <h2 id="the-problem">The problem</h2> <p>Canvas editor, 500 layers, the user drags layer #200 onto position #450. If the order is stored as plain integers <code>1, 2, 3, ..., 500</code>, moving a single element means renumbering every element after the insertion point.</p> <p>Tolerable for a local app. In a collaborative setting it&rsquo;s a nightmare:</p> <ul> <li>Every index update is a separate operation that can conflict with other users&rsquo; actions.</li> <li>Moving one layer means 250 index mutations, one per element between the old and new position.</li> <li>If two people drag different layers at the same moment, merging becomes a problem of reconstructing order rather than applying two patches.</li> </ul> <p>What you want: <strong>O(1)</strong> insert, and <strong>existing elements stay untouched</strong>.</p>