https://jayreddinjr-jr-odysseus-hf.hf.space/static/js/editor/checkerboard.js

1/**
2 * Paint a transparency-checkerboard pattern across the given canvas
3 * context. The editor uses this beneath every layer pass so empty
4 * (transparent) areas of the document are visible.
5 *
6 * Pure function — depends only on its arguments.
7 *
8 * @param {CanvasRenderingContext2D} ctx
9 * @param {number} w  Width in canvas pixels.
10 * @param {number} h  Height in canvas pixels.
11 */
12export function drawCheckerboard(ctx, w, h) {
13  const size = 10;
14  ctx.fillStyle = '#ccc';
15  ctx.fillRect(0, 0, w, h);
16  ctx.fillStyle = '#fff';
17  for (let y = 0; y < h; y += size) {
18    for (let x = 0; x < w; x += size) {
19      if ((Math.floor(x / size) + Math.floor(y / size)) % 2 === 0) {
20        ctx.fillRect(x, y, size, size);
21      }
22    }
23  }
24}