How to execute a compute shader before a vertex shader, and pass a shared buffer from one to another?

[dennisorlando]

Hi, I'm trying to use bevy's rendering system but I keep getting completely lost.
What I would like to achieve is supposedly simple:

1. a GPU buffer containing particle data (only their positions)
2. a Compute shader which updates particle positions each frame
3. a Vertex shader which draws such particles using such buffer (using instanced rendering)

I'm able to separately create 2. and 3. utilizing the two relevant examples ("gpu_drawback.rs" and "custom_shader_instancing.rs"), but the structs and methods used in those examples are so different that I have no idea how to combine them together; I'm not even sure where to start.
The instancing example uses a render_resources::Buffer to store instance data; can I just change it to a render_resources::StorageBuffer without any complaints, so that I can then feed that to the compute shader?
But, most importantly: how do I pipeline the compute shader before the vertex shader? The examples show two different approaches, one using something like a custom Render Node ("gpu_readback.rs") and the other ("custom_shader_instancing.rs") doing some weird stuff with... what I can only describe as "Dependency Injection wet dream". What even are e.g. DrawFunctions, Pipelines, Pipeline keys, "ViewSortedRenderPhases"? As you can tell, I'm very (very) confused (and lost)

[Henauxg]

I am not, knowledgeable enough on the Bevy render pipeline to give you a precise answer. However, there is this quite obscure to discover but extremely useful document https://hackmd.io/@bevy/rendering_summary that you might benefit from.