compute-shader mesh generation example

[ChristopherBiscardi]

Objective

People have been asking how to get a compute shader-built mesh into bevy's "stuff".

Some people want to control the lifetime of the mesh via Handle, and others don't don't how to set data in bind groups.

Solution

a new example that shows how to initialize a mesh handle with a render_world usage mesh, and then put the output of the compute shader into the mesh_allocator slab for the mesh.

The demo creates a scene with a camera, light, a circular base mesh, and an empty "cube to be" mesh that is shared by cloning the handle across two entities. The compute shader then fills in the data directly into the mesh_allocator slabs for the vertex/index buffers.

If the compute shader failed, there would be no cube meshes showing as the data would be empty.

Testing

cargo run --example compute_mesh

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Showcase

[github-actions]

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[JMS55]

I can't remember if this is right or not. I think you may need to order it vs the camera driver node?

[ChristopherBiscardi]

I added the edge here, but I'm really not sure it has any impact here (but it definitely doesn't hurt). Figuring out what the render graph actually looks like could use some debug visualization. Maybe a function that returns a dotviz 🤔

[tychedelia]

thanks!! i've wanted this for a while but only hesitated because i've felt like it should be easier. i have some ideas though and so think this will be a good target to improve things incrementally here

[IceSentry]

This feels a bit off. It seems weird that this needs to modify a global resource. But I'm not sure if there's a better alternative

[ChristopherBiscardi]

It feels like something that should be configurable by inserting a Resource or similar rather than modifying this one, yeah. but the MeshAllocator fields are private and initializing it using its FromWorld implementation is probably more awkward (it also has ordering requirements with other resources).

I also wanted to pass the BufferSlice to the shader instead of the full buffer, but I don't think the offsets match the storage buffer offset requirements (it was 256 on my machine and the offsets I saw were numbers like 4, 12, etc)

[IceSentry]

Could you make it so the cubes aren't clipping the circle mesh? I don't generally comment about the look of examples but it looks a bit strange in it's current state.

Also, if I'm reading this correctly this ends up modifying the mesh every frame right? I'd suggest maybe changing the scale every frame to show this is happening.

[ChristopherBiscardi]

Could you make it so the cubes aren't clipping the circle mesh?

Updated.

Also, if I'm reading this correctly this ends up modifying the mesh every frame right? I'd suggest maybe changing the scale every frame to show this is happening.

I instead updated this so that it will only generate once per unique GenerateMesh. I envision this particular example to be more of a "generate the N chunks around a player" as they move through a world, so continuing to generate every frame doesn't make sense.