# Objective
Closes#18075
In order to enable a number of patterns for dynamic materials in the
engine, it's necessary to decouple the renderer from the `Material`
trait.
This opens the possibility for:
- Materials that aren't coupled to `AsBindGroup`.
- 2d using the underlying 3d bindless infrastructure.
- Dynamic materials that can change their layout at runtime.
- Materials that aren't even backed by a Rust struct at all.
## Solution
In short, remove all trait bounds from render world material systems and
resources. This means moving a bunch of stuff onto `MaterialProperties`
and engaging in some hacks to make specialization work. Rather than
storing the bind group data in `MaterialBindGroupAllocator`, right now
we're storing it in a closure on `MaterialProperties`. TBD if this has
bad performance characteristics.
## Benchmarks
- `many_cubes`:
`cargo run --example many_cubes --release --features=bevy/trace_tracy --
--vary-material-data-per-instance`:
- @DGriffin91's Caldera
`cargo run --release --features=bevy/trace_tracy -- --random-materials`
- @DGriffin91's Caldera with 20 unique material types (i.e.
`MaterialPlugin<M>`) and random materials per mesh
`cargo run --release --features=bevy/trace_tracy -- --random-materials`
### TODO
- We almost certainly lost some parallelization from removing the type
params that could be gained back from smarter iteration.
- Test all the things that could have broken.
- ~Fix meshlets~
## Showcase
See [the
example](https://github.com/bevyengine/bevy/pull/19667/files#diff-9d768cfe1c3aa81eff365d250d3cbe5a63e8df63e81dd85f64c3c3cd993f6d94)
for a custom material implemented without the use of the `Material`
trait and thus `AsBindGroup`.
---------
Co-authored-by: IceSentry <IceSentry@users.noreply.github.com>
Co-authored-by: IceSentry <c.giguere42@gmail.com>
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