Creating custom UI using WebUI

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Custom UI in VU (aka WebUI) is based on modern web technologies such as HTML, CSS, and JavaScript. WebUI is essentially a website overlayed on top of the game view, and integrated with the various different subsystems. WebUI is using the Chromium web engine internally, so as long as what you're creating works on Chrome, it should also work in-game.

Creating your UI

First of all, create a new folder somewhere in your computer. Inside this folder, create a new file named index.html. This will be the entry point to your custom UI and is the first page that will be presented to the user. For now, we'll put something simple in it in the form of a hello world message:

<!DOCTYPE html>
    Hello world!

Compiling a WebUI package

Before the UI can be used by a VU client, it must be compiled using the WebUI compiler (vuicc.exe). Download the latest version of the compiler from here and place it somewhere in your computer. Then, open a command prompt (like PowerShell or cmd) and compile the WebUI package using the following command:

vuicc.exe "C:\path\to\your\ui" "C:\path\to\compiled\ui.vuic"

Where C:\path\to\your\ui points to the folder where you previously created the index.html file and C:\path\to\compiled\ui.vuic points to the file where you want to write the compiled WebUI package to. You could name that file whatever you want, but when you want to use it with your mod you'll have to rename it to ui.vuic so it's recommended to always use that name. You will need that file in the next step to integrate it with your mod.

Running your custom UI

Before you can proceed, make sure you've created a mod and set up a local server by following the getting started guide. Then, place the ui.vuic inside your mod folder (next to mod.json) and add a HasWebUI field with the value true inside your mod.json file. It should end up looking something like this:

    "Name": "My mod",
    "Description": "My incredible mod",
    "Version": "1.0.0",
    "HasVeniceEXT": true,
    "HasWebUI": true,

You must then add some code inside your client scripts to initialize the WebUI when the user joins the server. Inside your client __init__.lua script (or any other client script that gets loaded on startup) add the following code:

Events:Subscribe('Extension:Loaded', function()

This makes it so as soon as the mod gets loaded, the WebUI gets initialized and starts getting rendered on the user's screen. You can then start your server and join it, and you should be able to see the Hello world! text on your screen.

Managing input and display order

Since multiple WebUI frames can be active at a give time, one will be displayed on top of the other. Also, the game will often disable UI input, which means that a user will not be able to interact with your UI (such as when a user spawns in-game). Using JavaScript, the UI can request input from the game and change its display order.

WebUI frames have a global function that can be used to interact with the modding engine: WebUI.Call(...). The first parameter to this function is the operation the WebUI wants to perform and the rest are parameters to that operation (where relevant). For example, here's how you would enable keyboard input in your UI:


Here's the full list of commands that can be used to control input and display order:


Brings this WebUI frame to the front, placing it on top of all other frames. This is useful for when the frame intends to receive input.


Sends this WebUI frame to the back, placing it behind all other frames.


Enables keyboard input for this frame. This means that any key inputs will be sent to the WebUI.


Disables keyboard input and returns control to the game.


Resets the keyboard input to its expected in-game state.


Enables mouse input for this frame. This will show a cursor in-game and any mouse input will be passed to the WebUI.


Disables mouse input and returns control to the game.


Resets the mouse input to its expected in-game state.


Hides the WebUI frame.


Shows the WebUI frame.

Communicating with VeniceEXT

Since WebUI frames by themselves cannot directly interact with the game, VU provides a way to communicate with the VeniceEXT scripting engine in both ways. WebUI frames have the ability to raise VeniceEXT events, which can be subscribed to and handled from a client-side script (for more information about events see the events guide). This is possible via the global WebUI.Call(...) function as seen below:

WebUI.Call('DispatchEvent', 'EventName', 123)

The first parameter after DispatchEvent is the name of the event to dispatch, and the parameter after that is the value to pass to it. Dispatched events only support one parameter, so a common pattern is to create a JS object, JSON.stringify it, and then json.decode it from the VeniceEXT side. There is also the DispatchEventLocal variation of this call which will only dispatch the event to the current mod instead of all of them.

From the VeniceEXT side, scripts can execute JavaScript code on the WebUI frame as seen below:

WebUI:ExecuteJS('console.log("hello world");')

For more information on the available interactions between VeniceEXT and the WebUIU refer to the WebUI integration guide.

Debugging your UI

You can debug your WebUI on the fly by using the Chromium Dev Tools. To enable the tools, launch the VU client with the -dwebui launch argment:

vu.exe -dwebui

This will make the dev tools available locally on your computer at http://localhost:8884. Simply navigate to that webpage using the Chrome web browser (or any chromium-based browser) after having joined your server, and you'll be able to see a list of UIs for all the loaded mods. Keep in mind that the list will include the main menu UI and messing with it might break your client. Simply click on your mod from the list and you'll get a live view of your UI in the dev tools.

Using Frostbite textures

The WebUI can also access some Frostbite textures as images directly from HTML. To use a Frostbite texture, find its asset name (eg. Textures/Some/Texture) and then use it as a url with the fb:// prefix. For example, you would use it with an img tag as such:

<img src="fb://Textures/Some/Texture" />

Keep in mind that not all texture types are supported and most textures will not be available until the level has loaded, so make sure to display them at an appropriate time.

Making your UI responsive

The general rules for web responsiveness don't really apply to game UIs. While websites are supposed to maintain the sizing of the content and adapt it to the size of the screen, game UIs must scale the entire content based on the window's resolution. An easy way to achieve this in web terms is to use relative size units such as vh.

For example, the VU main menu is fully responsive with a minimum expected aspect ratio of 4:3. This means that all the content of the UI can fit within a 4:3 box and scale appropriately to wider aspect ratios. The menu was initially designed for 1080p screens but has been made responsive by making all size units relative to the view's height. That means that the taller the window is, the bigger the content is, while screen width doesn't affect it (for example in Ultrawide or multi-monitor setups). To calculate the sizes in vh units, the original pixel size was taken as a percentage of 1080 (the design resolution). For example, a box of width 200px and height 400px will be made to use a width of ((200 / 1080) * 100)vh (= 18.51851851851852vh) and a height of ((400 / 1080) * 100)vh (= 37.03703703703704vh).

By using relative sizing for everything, you can very easily make your UI responsive and able to accomodate different screen sizes and aspect ratios.

Last modified October 3, 2020: Fix vuicc usage example (7c43224)