Needed features to use superconductor as drop in for bevy_pbr

[dekuraan]

Essential:

• Use bevy Transforms
• Pull Camera from ActiveCamera

Very Useful:

• Use bevy_render's RenderGraph so we can easily add render plugins (see bevy_pbr impl)

Nice to have:

• compatibility with bevy_render/bevy_pbr's primitives
• compatibility with bevy_asset's assets

[dekuraan]

I believe your asset system is the way it is for a reason, so if the current asset system is better than bevy_asset I think there is no need to use bevy_asset

[expenses]

So tbh I'm not 100% convinced on the value of being a drop-in replacement, as I think that bevy_render has made some compromises that we'd benefit from avoiding. That said, it'd be great to get rid of as many unnecessary differences in the APIs as possible.

• Use bevy Transforms

Bevy transforms allow for non-uniform (where each axis can have a different scale) scaling: https://docs.rs/bevy/latest/bevy/prelude/struct.Transform.html#structfield.scale.

Superconductor instances (we could just rename these transforms) do not:

superconductor/renderer-core/src/instance.rs

Lines 20 to 24 in c37edf5

	pub struct Instance {
	pub position: Vec3,
	pub scale: f32,
	pub rotation: glam::Quat,
	}

The justification here is that non-uniform scaling creates all sorts of problems for proper shading of models, and isn't frequently used to be worth supporting. I'm happy to change my mind on this if a case where we want to do a lot of non-uniform scaling though.

We can have a system that copies bevy Transforms to superconductor instances, with the uniform scale just being scale.x.max(scale.y).max(scale.z), but I'd advise against it.

• Pull Camera from ActiveCamera

It looks like this link has been messed up with bevy 0.8. I'm sure we could integrate bevy's camera system into the code though.

• Use bevy_render's RenderGraph so we can easily add render plugins (see bevy_pbr impl)

Looks possible, haven't looked into it yet. I think the most important question is whether we need to do anything fancy to let both superconductor and any render plugins use the wgpu device.

• compatibility with bevy_render/bevy_pbr's primitives

Which primitives would these be? https://docs.rs/bevy/latest/bevy/render/primitives/index.html?

• compatibility with bevy_asset's assets

The reason why I didn't do this before is that A) I already had an asset system I could use from https://github.com/expenses/mateversum and B) the asset server in bevy::asset looked a little over complicated for our needs. I also think it's beneficial for us to be able to control the assets and how they're loaded. Happy to look into this more.