Compute example

[samoylovfp]

Trying to fix Bevy-Rust-GPU/bevy-rust-gpu#20

Reading the sources of

• https://github.com/bevyengine/bevy/blob/v0.10.1/examples/shader/compute_shader_game_of_life.rs
• https://github.com/Bevy-Rust-GPU/example-workspace/blob/dcca3145122ce527672d60eee67efe5b1b69005b/bevy-app/crates/viewer/examples/simple-material.rs
• https://github.com/EmbarkStudios/rust-gpu/blob/795f433fdd1d01974bd48a5d810d85214b6606b4/examples/shaders/compute-shader/src/lib.rs

And trying to mash everything together

[ProfLander]

Thanks for putting in the effort on this - I've not had chance to test it yet, but if it runs and produces the expected output then I'd say it's a strong start!

[samoylovfp]

Not yet. I need to read more about how bevy handles shaders and didn't have the energy to do so yet. Planning on taking another stab this or the next weekend

[samoylovfp]

I hope that I am missing something obvious, but the ways of achieving the result, that I see, feel a bit backwards.

The current problem is that the bevy compute pipeline requires the bevy shader handle,
which in the bevy compute example is obtained by loading the shader from a path via an AssetServer.
For rust-gpu shader we first need to convert it into a bevy shader to build the compute pipeline.

I initially thought it will be easiest to just do this processing in the render graph node "update" method,
but seems like the render-sub-app's World does not provide the Assets<Shader> or Assets<RustGpuBuilderOutput>,
so I cannot just take the shader builder output, convert it and put into the Assets<Shader>. Maybe it is possible by converting them in the bevy app and then "extracting" them into the render world, but it seems more backwards than other solutions.

I think maybe at this point the most straightforward way is to provide a custom AssetLoader, that builds a bevy Shader out of the RustGpuBuilderOutput,
then the bevy compute example requires little change,
only the addition of the assetloader and the name of the shader,
maybe using the "hashpound fragment" syntax to indicate the entrypoint; I'll try that.

[samoylovfp]

I ended up in a situation where I think it should work, but it doesn't and it doesn't even complain that something is wrong.
I suspect I might have messed up the signature of the shader entrypoint, will try to debug it somehow

[samoylovfp]

I'll take another stab in two weeks unless someone figures it out sooner

[tombh]

Sounds like great progress, I'm excited to try it out!

[samoylovfp]

Wasn't able to debug why nothing is showing, lost the remainder of my motivation reading through the SPIR-V specification. Might take another stab in a few months

[tombh]

Ha yeah SPIR-V is pretty esoteric. Awesome work @samoylovfp 🙇

[tombh]

That's great! Did you mean to post a link to the branch? Or were just mentioning it? I see the link now.

Do you think the notably slower frame rate is because of Bevy's rust-gpu integration? Or just because your implementation is prioritising proof of concept for now?

[tombh]

That's a lot of great info and insight. Even if its slower, it's just great to know that it all works. I'm still a newbie to all this, so it'll take me a while to pore over everything.