Attention: Here be dragons

This is the latest (unstable) version of this documentation, which may document features not available in or compatible with released stable versions of Redot.

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Exporting for the Web¶

WebGL version¶

Redot 4.0 and later can only target WebGL 2.0 (using the Compatibility rendering method). There is no stable way to run Vulkan applications on the web yet.

See Can I use WebGL 2.0 for a list of browser versions supporting WebGL 2.0. Note that Safari has several issues with WebGL 2.0 support that other browsers don't have, so we recommend using a Chromium-based browser or Firefox if possible.

Export options¶

If a runnable web export template is available, a button appears between the Stop scene and Play edited Scene buttons in the editor to quickly open the game in the default browser for testing.

If your project uses GDExtension Extension Support needs to be enabled.

If you plan to use VRAM compression make sure that Vram Texture Compression is enabled for the targeted platforms (enabling both For Desktop and For Mobile will result in a bigger, but more compatible export).

If a path to a Custom HTML shell file is given, it will be used instead of the default HTML page. See Custom HTML page for Web export.

Head Include is appended into the <head> element of the generated HTML page. This allows to, for example, load webfonts and third-party JavaScript APIs, include CSS, or run JavaScript code.

Important

Each project must generate their own HTML file. On export, several text placeholders are replaced in the generated HTML file specifically for the given export options. Any direct modifications to that HTML file will be lost in future exports. To customize the generated file, use the Custom HTML shell option.

Limitations¶

For security and privacy reasons, many features that work effortlessly on native platforms are more complicated on the web platform. Following is a list of limitations you should be aware of when porting a Redot game to the web.

Important

Browser vendors are making more and more functionalities only available in secure contexts, this means that such features are only be available if the web page is served via a secure HTTPS connection (localhost is usually exempt from such requirement).

Using cookies for data persistence¶

Users must allow cookies (specifically IndexedDB) if persistence of the user:// file system is desired. When playing a game presented in an iframe, third-party cookies must also be enabled. Incognito/private browsing mode also prevents persistence.

The method OS.is_userfs_persistent() can be used to check if the user:// file system is persistent, but can give false positives in some cases.

Background processing¶

The project will be paused by the browser when the tab is no longer the active tab in the user's browser. This means functions such as _process() and _physics_process() will no longer run until the tab is made active again by the user (by switching back to the tab). This can cause networked games to disconnect if the user switches tabs for a long duration.

This limitation does not apply to unfocused browser windows. Therefore, on the user's side, this can be worked around by running the project in a separate window instead of a separate tab.

Full screen and mouse capture¶

Browsers do not allow arbitrarily entering full screen. The same goes for capturing the cursor. Instead, these actions have to occur as a response to a JavaScript input event. In Redot, this means entering full screen from within a pressed input event callback such as _input or _unhandled_input. Querying the class_Input singleton is not sufficient, the relevant input event must currently be active.

For the same reason, the full screen project setting doesn't work unless the engine is started from within a valid input event handler. This requires customization of the HTML page.

Audio¶

Some browsers restrict autoplay for audio on websites. The easiest way around this limitation is to request the player to click, tap or press a key/button to enable audio, for instance when displaying a splash screen at the start of your game.

Networking¶

Low level networking is not implemented due to lacking support in browsers.

Currently, only HTTP client, HTTP requests, WebSocket (client) and WebRTC are supported.

The HTTP classes also have several restrictions on the HTML5 platform:

Accessing or changing the StreamPeer is not possible

Threaded/Blocking mode is not available

Cannot progress more than once per frame, so polling in a loop will freeze

No chunked responses

Host verification cannot be disabled

Subject to same-origin policy

Clipboard¶

Clipboard synchronization between engine and the operating system requires a browser supporting the Clipboard API, additionally, due to the API asynchronous nature might not be reliable when accessed from GDScript.

Warning

Requires a secure context.

Gamepads¶

Gamepads will not be detected until one of their button is pressed. Gamepads might have the wrong mapping depending on the browser/OS/gamepad combination, sadly the Gamepad API does not provide a reliable way to detect the gamepad information necessary to remap them based on model/vendor/OS due to privacy considerations.

Warning

Requires a secure context.

Boot splash is not displayed¶

The default HTML page does not display the boot splash while loading. However, the image is exported as a PNG file, so custom HTML pages can display it.

Serving the files¶

Exporting for the web generates several files to be served from a web server, including a default HTML page for presentation. A custom HTML file can be used, see Custom HTML page for Web export.

Warning

To ensure low audio latency and the ability to use class_Thread in web exports, Redot 4 web exports always use SharedArrayBuffer. This requires a secure context, while also requiring the following CORS headers to be set when serving the files:

Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: require-corp

If you don't control the web server or are unable to add response headers, use coi-serviceworker as a workaround.

If the client doesn't receive the required response headers, the project will not run.

The generated .html file can be used as DirectoryIndex in Apache servers and can be renamed to e.g. index.html at any time. Its name is never depended on by default.

The HTML page draws the game at maximum size within the browser window. This way, it can be inserted into an <iframe> with the game's size, as is common on most web game hosting sites.

The other exported files are served as they are, next to the .html file, names unchanged. The .wasm file is a binary WebAssembly module implementing the engine. The .pck file is the Redot main pack containing your game. The .js file contains start-up code and is used by the .html file to access the engine. The .png file contains the boot splash image. It is not used in the default HTML page, but is included for custom HTML pages.

The .pck file is binary, usually delivered with the MIME-type application/octet-stream. The .wasm file is delivered as application/wasm.

Warning

Delivering the WebAssembly module (.wasm) with a MIME-type other than application/wasm can prevent some start-up optimizations.

Delivering the files with server-side compression is recommended especially for the .pck and .wasm files, which are usually large in size. The WebAssembly module compresses particularly well, down to around a quarter of its original size with gzip compression. Consider using Brotli precompression if supported on your web server for further file size savings.

Hosts that provide on-the-fly compression: GitHub Pages (gzip)

Hosts that don't provide on-the-fly compression: itch.io, GitLab Pages (supports manual gzip precompression)

Tip

The Redot repository includes a Python script to host a local web server. This script is intended for testing the web editor, but it can also be used to test exported projects.

Save the linked script to a file called serve.py, move this file to the folder containing the exported project's index.html, then run the following command in a command prompt within the same folder:

# You may need to replace `python` with `python3` on some platforms.
python serve.py --root .

On Windows, you can open a command prompt in the current folder by holding Shift and right-clicking on empty space in Windows Explorer, then choosing Open PowerShell window here.

This will serve the contents of the current folder and open the default web browser automatically.

Note that for production use cases, this Python-based web server should not be used. Instead, you should use an established web server such as Apache or nginx.

Interacting with the browser and JavaScript¶

See the dedicated page on how to interact with JavaScript and access some unique Web browser features.

Environment variables¶

You can use the following environment variables to set export options outside of the editor. During the export process, these override the values that you set in the export menu.

HTML5 export environment variables¶
Export option	Environment variable
Encryption / Encryption Key	`GODOT_SCRIPT_ENCRYPTION_KEY`