improve compile time by type-erasing wgpu structs (#5950)
# Objective
structs containing wgpu types take a long time to compile. this is particularly bad for generics containing the wgpu structs (like the depth pipeline builder with `#[derive(SystemParam)]` i've been working on).
we can avoid that by boxing and type-erasing in the bevy `render_resource` wrappers.
type system magic is not a strength of mine so i guess there will be a cleaner way to achieve this, happy to take feedback or for it to be taken as a proof of concept if someone else wants to do a better job.
## Solution
- add macros to box and type-erase in debug mode
- leave current impl for release mode
timings:
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current | | |
-- | -- | -- | --
| Total time: | 64.9s |
| bevy_pbr v0.9.0-dev | 19.2s |
| bevy_render v0.9.0-dev | 17.0s |
| bevy_sprite v0.9.0-dev | 15.1s |
| DepthPipelineBuilder | 18.7s |
| | |
with type-erasing | | | diff
| Total time: | 49.0s | -24%
| bevy_render v0.9.0-dev | 12.0s | -38%
| bevy_pbr v0.9.0-dev | 8.7s | -49%
| bevy_sprite v0.9.0-dev | 6.1s | -60%
| DepthPipelineBuilder | 1.2s | -94%
</body>
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the depth pipeline builder is a binary with body:
```rust
use std::{marker::PhantomData, hash::Hash};
use bevy::{prelude::*, ecs::system::SystemParam, pbr::{RenderMaterials, MaterialPipeline, ShadowPipeline}, render::{renderer::RenderDevice, render_resource::{SpecializedMeshPipelines, PipelineCache}, render_asset::RenderAssets}};
fn main() {
println!("Hello, world p!\n");
}
#[derive(SystemParam)]
pub struct DepthPipelineBuilder<'w, 's, M: Material>
where M::Data: Eq + Hash + Clone,
{
render_device: Res<'w, RenderDevice>,
material_pipeline: Res<'w, MaterialPipeline<M>>,
material_pipelines: ResMut<'w, SpecializedMeshPipelines<MaterialPipeline<M>>>,
shadow_pipeline: Res<'w, ShadowPipeline>,
pipeline_cache: ResMut<'w, PipelineCache>,
render_meshes: Res<'w, RenderAssets<Mesh>>,
render_materials: Res<'w, RenderMaterials<M>>,
msaa: Res<'w, Msaa>,
#[system_param(ignore)]
_p: PhantomData<&'s M>,
}
```
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