Unity in worker using transferControlToOffscreen

We using Unity webgl in our game. Freezing at start is very annoying So I decided to try a new feature Canvas.transferControlToOffscreen() to start Unity in a worker.

I copied Framework (builded js code) and successfully compiled and instantiated module in a worker.
Everything is fine and Module.asm._main() was called.
But Engine crashes without any meaningful reason.

Loading player data from data.unity3d

Initialize engine version: 2018.3.5f1 (76b3e37670a4)

PlatformGetStacktrace

Could not initialize WebGL context. Failed starting Unity.

     at wasm-function[2306]:37

     at wasm-function[2291]:597

     at wasm-function[7951]:109

     at wasm-function[7912]:668

     at wasm-function[7901]:54

     at wasm-function[7881]:21

     at wasm-function[7826]:996 

(Filename:  Line: 699)

Is it possible to run Unity in a worker?
I added Module.ENVIRONMENT = 'WORKER' but it didn`t help.

 

You ~might~ have some luck if you compile with the emscriptenArgs flag -s OFFSCREEN_CANVAS_SUPPORT=1. The only other issue I ran into was a mysterious undefined GLctxIsOnParentThread variable in the wasm.framework.unityweb file which didn't seem to mind being removed.

I suspect it might not be this easy though.

 

Yep, it wasn`t.

 

Success!
https://xcraft.ru/battle/index.php?battle_id=8ab4f53cdd0dcc860b9f66fc89aff79a&anim3d=1
Chrome 69+ only (and Opera based on this version)

It works without this flag

P.s. link is not the best, but its available without registration.

 

Interesting.. how did you manage to get it working in the end? I was under the impression the browser offscreen canvas support was around for a little longer before Chrome 69 but I might be mistaken. I'd be curious how feasible it is to implement a fallback for older browsers as well.

Nice job by the way!

 

The main feature you need is transferControlToOffscreen.
You taking canvas from the DOM, call transferControlToOffscreen() and getting OffscreenCanvas instance (all in main thread)
And here you get two things:
1. Everything you draw on OffscreenCanvas will be mirrored to DOM`s canvas
2. OffscreenCanvas is Transferable - can be transfer from main thread to the worker

So you just need to start Unity instance in a worker with transfered offscreen canvas

The main problem that Unity expects some properties like window, style, addEventListener... You`ll need to bypass all of them.

It was easier for me because earlier I refused to use UnityLoader.js. I have my own 300 line`s script to load wasm code, it uses streamingCompilation by the way

 

Neat, I'll give that a go. This should make it easier for us to handle our authentication flow during load rather than after WebGL has loaded, among other potential changes. A custom loader shouldn't be an issue for us.

 

Look at

Module['locateFile']

if you are using 2018.* version

 

Very interesting! Did putting Unity in a separate worker reduce the freezing? Kind of a bummer it's only on Chrome atm (although perhaps behind a flag in firefox).

 

Firefox should support it too (and since much earlier) - looking at the feature matrix here:
https://developer.mozilla.org/en-US/docs/Web/API/OffscreenCanvas

Unfortunately it's not enabled by default in Firefox though.

 

Do you think that Safari will also support it?

 

I tried with enabled flag - tab always crashes.

 

I`m sure about it, but the most important question "When?"

 

I managed to get it working with a slightly modified UnityLoader.js (mainly just changing the loadCode function to use JS Worker's importScripts function instead of loading things by importing a <script> element, and grabbing the eventhandler proxy logic from your own example.

I wasn't aware that unfortunately it doesn't seem to support a WebGL 2 context yet which is a shame (even though I'm not really using any WebGL 2 specific features right now).

I've attached an extremely minimal example that includes the index.html, an offscreencanvas.js file (the JS worker) and an unminified, slightly modified UnityLoader.js - keep in mind that since it is super minimal it doesn't actually pass events to/from the main thread, or more importantly handle regular load fallback if OffscreenCanvas isn't supported. It's more an example .