Inconsistent Rendering with Webassembly on lower-end hardware. Game chokes.

[LarsDu]

Bevy version

main
The release number or commit hash of the version you're using.

[dependencies.bevy]
git = "https://github.com/bevyengine/bevy.git"
rev = "543465b721048355e34eb6078923645747c1d44b"

[Optional] Relevant system information

105.0.1 (64-bit)

Mac OSX Monterrey 12.5
  Processor Name:	Quad-Core Intel Core i7
  Processor Speed:	2.6 GHz
  Number of Processors:	1
  Total Number of Cores:	4
  L2 Cache (per Core):	256 KB
  L3 Cache:	6 MB
  Hyper-Threading Technology:	Enabled
  Memory:	16 GB

Numerous reports from people I shared this game with indicated that the web assembly build is slow, stalls, or crashes.

I've tried it on 3 different machines (1 Skylake PC running Ubuntu 22.04, an M1 Mac, and on the above listed laptop). On the above listed laptop certain models do not get shaded or lit correctly. All build choke for at least 2 seconds after pressing the start button.
I suspect there is some sort of threading issue.

If you cannot get Bevy to build or run on your machine, please include:

• the Rust version you're using (you can get this by running cargo --version)

cargo 1.63.0 (fd9c4297c 2022-07-01)

If your bug is rendering-related, copy the adapter info that appears when you run Bevy.

What you did

Play the webassembly build of the above-linked game

Describe how you arrived at the problem. If you can, consider providing a code snippet or link.

What went wrong

If it's not clear, break this out into:

• what were you expecting?
  Significantly better performance for WASM builds given the engine and language being used.
• what actually happened?
  Very poor performance on WASM builds.

[rparrett]

The main issue is that Bevy is not multi-threaded at all on wasm. This is a known limitation (for now).

Anything doing heavy work on the CPU is going to create hiccups:

• Audio decoding
• Render pipeline creation
• GLTF parsing
• Probably other stuff

You can work around this somewhat by frontloading these things into a loading state in your app.

François' entry from Bevy Jam 2 (source) is the only example I know of that waits on pipeline creation in its loading state.

Subfuse, another entry from Bevy Jam 2 is a great demo of what's currently possible with 3d games on the web.

There are also some known issues with intel gpus that you may be seeing:

#3315
#4354

etc. That's probably not comprehensive.

[gilescope]

You can have multiple processes running on wasm if you can offload some processing to another process and the serialisation overhead of the results isn't an issue: https://github.com/thedodd/trunk/tree/master/examples/webworker-gloo - I've got that working ok with bevy wasm.
That said it would be nice to get stats on how much time all of my various systems are taking and which are parallel and which are not run in parallel. Flamegraph doesn't seem to give that detail...

[kauly]

Hey @gilescope, can you provide an example of bevy wasm and webworker-gloo? Im trying to understand how this work, do you put system/plugins inside of the worker?