gridcraft/packaging/web/README.md

Hosting GridCraft for the web

gridcraft-web-<version>.zip (from the GitHub release, or packaging/web/package.sh) holds a static site in gridcraft-web-<version>/:

File	What it is
index.html	The page. It loads everything through relative URLs.
gridcraft-web-<hash>.js	wasm-bindgen glue (generated, ES module)
gridcraft-web-<hash>_bg.wasm	The app (compresses to roughly a third with gzip/Brotli)
_headers, .htaccess	Sample header rules for Netlify/Cloudflare Pages and Apache

There is no server-side code. Upload the folder's contents anywhere that serves static files.

Any path works

All URLs in index.html are relative (public_url = "./" in apps/gridcraft-web/Trunk.toml), so the site works at a domain root (https://example.com/), under a prefix (https://example.com/tools/gridcraft/) and from a CDN bucket. The asset names carry a content hash, so they can be cached forever. Only index.html needs revalidation.

Required server settings

• MIME type: serve .wasm as application/wasm. Browsers refuse to stream-compile it under any other type, and the app then loads slowly or not at all. Serve .js as text/javascript. Most hosts already do both. For nginx, check that mime.types has application/wasm wasm;.
• Compression: turn on gzip or Brotli for .wasm, .js and .html. That cuts the download to roughly a third. You can also precompress (brotli -k *.wasm) and let the server send Content-Encoding: br.
• Caching: Cache-Control: public, max-age=31536000, immutable on the hashed .wasm and .js files, and no-cache on index.html.
• HTTPS: WebGPU (and the clipboard) only work in a secure context, which means https:// or http://localhost. Over plain HTTP elsewhere, the app falls back to WebGL2.
• No special isolation headers: GridCraft doesn't use SharedArrayBuffer, so it doesn't need Cross-Origin-Opener-Policy or Cross-Origin-Embedder-Policy. If your site already sends COEP require-corp, also send Cross-Origin-Resource-Policy: same-origin (or cross-origin when the files live on a CDN) on the app's files.

nginx example:

location /gridcraft/ {
    types { application/wasm wasm; text/javascript js; text/html html; }
    gzip on;
    gzip_types application/wasm text/javascript text/html;
    location ~* \.(wasm|js)$ { add_header Cache-Control "public, max-age=31536000, immutable"; }
    location ~* index\.html$ { add_header Cache-Control "no-cache"; }
}

Local test: python3 -m http.server 8765 inside the folder, then open http://localhost:8765/.

Embedding in a page (iframe)

<iframe
  src="https://example.com/gridcraft/"
  title="GridCraft spreadsheet"
  style="width: 100%; height: 720px; border: 0;"
  allow="fullscreen; clipboard-read; clipboard-write"
  allowfullscreen>
</iframe>

• The app fills the iframe and follows its size, so size the iframe and not the app.
• Keyboard shortcuts go to the iframe after the user clicks into it, as with any embedded app.
• Cross-origin embeds work. Preferences are kept in the iframe's localStorage. Browsers that partition or block third-party storage may forget them between visits, and the app then starts with defaults.
• Sandboxed iframes need at least sandbox="allow-scripts allow-same-origin allow-downloads allow-popups". Without allow-same-origin there's no storage. Without allow-downloads, Save and Export (browser downloads) are blocked.
• Don't send X-Frame-Options: DENY or a frame-ancestors CSP that excludes the embedding page.
• Window chrome: ?chrome=none on the iframe src leaves out the title bar and the File tab (whose Backstage view then never opens); ?chrome=notitlebar or ?chrome=nofiletab leave out just one. Use them when the host window already shows the file name and owns the files, so the sheet's own Open or Save As cannot replace what the host thinks is open. Everything stays on by default.

Renderer selection

GridCraft's web build is the same egui app as the desktop one, compiled to wasm (apps/gridcraft-web). It renders with the backend apps/gridcraft-web selects (WebGPU where available, otherwise WebGL2). If the web app adds URL flags to force a backend (as the sibling Craft apps do with ?webgl / ?cpu), document them here; they also work on the iframe src.

A browser with neither WebGPU nor WebGL2 gets a message in place of the app.