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https://github.com/bevyengine/bevy
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6 commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
François
|
814f8d1635 |
update wgpu to 0.13 (#5168)
# Objective - Update wgpu to 0.13 - ~~Wait, is wgpu 0.13 released? No, but I had most of the changes already ready since playing with webgpu~~ well it has been released now - Also update parking_lot to 0.12 and naga to 0.9 ## Solution - Update syntax for wgsl shaders https://github.com/gfx-rs/wgpu/blob/master/CHANGELOG.md#wgsl-syntax - Add a few options, remove some references: https://github.com/gfx-rs/wgpu/blob/master/CHANGELOG.md#other-breaking-changes - fragment inputs should now exactly match vertex outputs for locations, so I added exports for those to be able to reuse them https://github.com/gfx-rs/wgpu/pull/2704 |
||
Carter Anderson
|
747b0c69b0 |
Better Materials: AsBindGroup trait and derive, simpler Material trait (#5053)
# Objective
This PR reworks Bevy's Material system, making the user experience of defining Materials _much_ nicer. Bevy's previous material system leaves a lot to be desired:
* Materials require manually implementing the `RenderAsset` trait, which involves manually generating the bind group, handling gpu buffer data transfer, looking up image textures, etc. Even the simplest single-texture material involves writing ~80 unnecessary lines of code. This was never the long term plan.
* There are two material traits, which is confusing, hard to document, and often redundant: `Material` and `SpecializedMaterial`. `Material` implicitly implements `SpecializedMaterial`, and `SpecializedMaterial` is used in most high level apis to support both use cases. Most users shouldn't need to think about specialization at all (I consider it a "power-user tool"), so the fact that `SpecializedMaterial` is front-and-center in our apis is a miss.
* Implementing either material trait involves a lot of "type soup". The "prepared asset" parameter is particularly heinous: `&<Self as RenderAsset>::PreparedAsset`. Defining vertex and fragment shaders is also more verbose than it needs to be.
## Solution
Say hello to the new `Material` system:
```rust
#[derive(AsBindGroup, TypeUuid, Debug, Clone)]
#[uuid = "f690fdae-d598-45ab-8225-97e2a3f056e0"]
pub struct CoolMaterial {
#[uniform(0)]
color: Color,
#[texture(1)]
#[sampler(2)]
color_texture: Handle<Image>,
}
impl Material for CoolMaterial {
fn fragment_shader() -> ShaderRef {
"cool_material.wgsl".into()
}
}
```
Thats it! This same material would have required [~80 lines of complicated "type heavy" code](https://github.com/bevyengine/bevy/blob/v0.7.0/examples/shader/shader_material.rs) in the old Material system. Now it is just 14 lines of simple, readable code.
This is thanks to a new consolidated `Material` trait and the new `AsBindGroup` trait / derive.
### The new `Material` trait
The old "split" `Material` and `SpecializedMaterial` traits have been removed in favor of a new consolidated `Material` trait. All of the functions on the trait are optional.
The difficulty of implementing `Material` has been reduced by simplifying dataflow and removing type complexity:
```rust
// Old
impl Material for CustomMaterial {
fn fragment_shader(asset_server: &AssetServer) -> Option<Handle<Shader>> {
Some(asset_server.load("custom_material.wgsl"))
}
fn alpha_mode(render_asset: &<Self as RenderAsset>::PreparedAsset) -> AlphaMode {
render_asset.alpha_mode
}
}
// New
impl Material for CustomMaterial {
fn fragment_shader() -> ShaderRef {
"custom_material.wgsl".into()
}
fn alpha_mode(&self) -> AlphaMode {
self.alpha_mode
}
}
```
Specialization is still supported, but it is hidden by default under the `specialize()` function (more on this later).
### The `AsBindGroup` trait / derive
The `Material` trait now requires the `AsBindGroup` derive. This can be implemented manually relatively easily, but deriving it will almost always be preferable.
Field attributes like `uniform` and `texture` are used to define which fields should be bindings,
what their binding type is, and what index they should be bound at:
```rust
#[derive(AsBindGroup)]
struct CoolMaterial {
#[uniform(0)]
color: Color,
#[texture(1)]
#[sampler(2)]
color_texture: Handle<Image>,
}
```
In WGSL shaders, the binding looks like this:
```wgsl
struct CoolMaterial {
color: vec4<f32>;
};
[[group(1), binding(0)]]
var<uniform> material: CoolMaterial;
[[group(1), binding(1)]]
var color_texture: texture_2d<f32>;
[[group(1), binding(2)]]
var color_sampler: sampler;
```
Note that the "group" index is determined by the usage context. It is not defined in `AsBindGroup`. Bevy material bind groups are bound to group 1.
The following field-level attributes are supported:
* `uniform(BINDING_INDEX)`
* The field will be converted to a shader-compatible type using the `ShaderType` trait, written to a `Buffer`, and bound as a uniform. It can also be derived for custom structs.
* `texture(BINDING_INDEX)`
* This field's `Handle<Image>` will be used to look up the matching `Texture` gpu resource, which will be bound as a texture in shaders. The field will be assumed to implement `Into<Option<Handle<Image>>>`. In practice, most fields should be a `Handle<Image>` or `Option<Handle<Image>>`. If the value of an `Option<Handle<Image>>` is `None`, the new `FallbackImage` resource will be used instead. This attribute can be used in conjunction with a `sampler` binding attribute (with a different binding index).
* `sampler(BINDING_INDEX)`
* Behaves exactly like the `texture` attribute, but sets the Image's sampler binding instead of the texture.
Note that fields without field-level binding attributes will be ignored.
```rust
#[derive(AsBindGroup)]
struct CoolMaterial {
#[uniform(0)]
color: Color,
this_field_is_ignored: String,
}
```
As mentioned above, `Option<Handle<Image>>` is also supported:
```rust
#[derive(AsBindGroup)]
struct CoolMaterial {
#[uniform(0)]
color: Color,
#[texture(1)]
#[sampler(2)]
color_texture: Option<Handle<Image>>,
}
```
This is useful if you want a texture to be optional. When the value is `None`, the `FallbackImage` will be used for the binding instead, which defaults to "pure white".
Field uniforms with the same binding index will be combined into a single binding:
```rust
#[derive(AsBindGroup)]
struct CoolMaterial {
#[uniform(0)]
color: Color,
#[uniform(0)]
roughness: f32,
}
```
In WGSL shaders, the binding would look like this:
```wgsl
struct CoolMaterial {
color: vec4<f32>;
roughness: f32;
};
[[group(1), binding(0)]]
var<uniform> material: CoolMaterial;
```
Some less common scenarios will require "struct-level" attributes. These are the currently supported struct-level attributes:
* `uniform(BINDING_INDEX, ConvertedShaderType)`
* Similar to the field-level `uniform` attribute, but instead the entire `AsBindGroup` value is converted to `ConvertedShaderType`, which must implement `ShaderType`. This is useful if more complicated conversion logic is required.
* `bind_group_data(DataType)`
* The `AsBindGroup` type will be converted to some `DataType` using `Into<DataType>` and stored as `AsBindGroup::Data` as part of the `AsBindGroup::as_bind_group` call. This is useful if data needs to be stored alongside the generated bind group, such as a unique identifier for a material's bind group. The most common use case for this attribute is "shader pipeline specialization".
The previous `CoolMaterial` example illustrating "combining multiple field-level uniform attributes with the same binding index" can
also be equivalently represented with a single struct-level uniform attribute:
```rust
#[derive(AsBindGroup)]
#[uniform(0, CoolMaterialUniform)]
struct CoolMaterial {
color: Color,
roughness: f32,
}
#[derive(ShaderType)]
struct CoolMaterialUniform {
color: Color,
roughness: f32,
}
impl From<&CoolMaterial> for CoolMaterialUniform {
fn from(material: &CoolMaterial) -> CoolMaterialUniform {
CoolMaterialUniform {
color: material.color,
roughness: material.roughness,
}
}
}
```
### Material Specialization
Material shader specialization is now _much_ simpler:
```rust
#[derive(AsBindGroup, TypeUuid, Debug, Clone)]
#[uuid = "f690fdae-d598-45ab-8225-97e2a3f056e0"]
#[bind_group_data(CoolMaterialKey)]
struct CoolMaterial {
#[uniform(0)]
color: Color,
is_red: bool,
}
#[derive(Copy, Clone, Hash, Eq, PartialEq)]
struct CoolMaterialKey {
is_red: bool,
}
impl From<&CoolMaterial> for CoolMaterialKey {
fn from(material: &CoolMaterial) -> CoolMaterialKey {
CoolMaterialKey {
is_red: material.is_red,
}
}
}
impl Material for CoolMaterial {
fn fragment_shader() -> ShaderRef {
"cool_material.wgsl".into()
}
fn specialize(
pipeline: &MaterialPipeline<Self>,
descriptor: &mut RenderPipelineDescriptor,
layout: &MeshVertexBufferLayout,
key: MaterialPipelineKey<Self>,
) -> Result<(), SpecializedMeshPipelineError> {
if key.bind_group_data.is_red {
let fragment = descriptor.fragment.as_mut().unwrap();
fragment.shader_defs.push("IS_RED".to_string());
}
Ok(())
}
}
```
Setting `bind_group_data` is not required for specialization (it defaults to `()`). Scenarios like "custom vertex attributes" also benefit from this system:
```rust
impl Material for CustomMaterial {
fn vertex_shader() -> ShaderRef {
"custom_material.wgsl".into()
}
fn fragment_shader() -> ShaderRef {
"custom_material.wgsl".into()
}
fn specialize(
pipeline: &MaterialPipeline<Self>,
descriptor: &mut RenderPipelineDescriptor,
layout: &MeshVertexBufferLayout,
key: MaterialPipelineKey<Self>,
) -> Result<(), SpecializedMeshPipelineError> {
let vertex_layout = layout.get_layout(&[
Mesh::ATTRIBUTE_POSITION.at_shader_location(0),
ATTRIBUTE_BLEND_COLOR.at_shader_location(1),
])?;
descriptor.vertex.buffers = vec![vertex_layout];
Ok(())
}
}
```
### Ported `StandardMaterial` to the new `Material` system
Bevy's built-in PBR material uses the new Material system (including the AsBindGroup derive):
```rust
#[derive(AsBindGroup, Debug, Clone, TypeUuid)]
#[uuid = "7494888b-c082-457b-aacf-517228cc0c22"]
#[bind_group_data(StandardMaterialKey)]
#[uniform(0, StandardMaterialUniform)]
pub struct StandardMaterial {
pub base_color: Color,
#[texture(1)]
#[sampler(2)]
pub base_color_texture: Option<Handle<Image>>,
/* other fields omitted for brevity */
```
### Ported Bevy examples to the new `Material` system
The overall complexity of Bevy's "custom shader examples" has gone down significantly. Take a look at the diffs if you want a dopamine spike.
Please note that while this PR has a net increase in "lines of code", most of those extra lines come from added documentation. There is a significant reduction
in the overall complexity of the code (even accounting for the new derive logic).
---
## Changelog
### Added
* `AsBindGroup` trait and derive, which make it much easier to transfer data to the gpu and generate bind groups for a given type.
### Changed
* The old `Material` and `SpecializedMaterial` traits have been replaced by a consolidated (much simpler) `Material` trait. Materials no longer implement `RenderAsset`.
* `StandardMaterial` was ported to the new material system. There are no user-facing api changes to the `StandardMaterial` struct api, but it now implements `AsBindGroup` and `Material` instead of `RenderAsset` and `SpecializedMaterial`.
## Migration Guide
The Material system has been reworked to be much simpler. We've removed a lot of boilerplate with the new `AsBindGroup` derive and the `Material` trait is simpler as well!
### Bevy 0.7 (old)
```rust
#[derive(Debug, Clone, TypeUuid)]
#[uuid = "f690fdae-d598-45ab-8225-97e2a3f056e0"]
pub struct CustomMaterial {
color: Color,
color_texture: Handle<Image>,
}
#[derive(Clone)]
pub struct GpuCustomMaterial {
_buffer: Buffer,
bind_group: BindGroup,
}
impl RenderAsset for CustomMaterial {
type ExtractedAsset = CustomMaterial;
type PreparedAsset = GpuCustomMaterial;
type Param = (SRes<RenderDevice>, SRes<MaterialPipeline<Self>>);
fn extract_asset(&self) -> Self::ExtractedAsset {
self.clone()
}
fn prepare_asset(
extracted_asset: Self::ExtractedAsset,
(render_device, material_pipeline): &mut SystemParamItem<Self::Param>,
) -> Result<Self::PreparedAsset, PrepareAssetError<Self::ExtractedAsset>> {
let color = Vec4::from_slice(&extracted_asset.color.as_linear_rgba_f32());
let byte_buffer = [0u8; Vec4::SIZE.get() as usize];
let mut buffer = encase::UniformBuffer::new(byte_buffer);
buffer.write(&color).unwrap();
let buffer = render_device.create_buffer_with_data(&BufferInitDescriptor {
contents: buffer.as_ref(),
label: None,
usage: BufferUsages::UNIFORM | BufferUsages::COPY_DST,
});
let (texture_view, texture_sampler) = if let Some(result) = material_pipeline
.mesh_pipeline
.get_image_texture(gpu_images, &Some(extracted_asset.color_texture.clone()))
{
result
} else {
return Err(PrepareAssetError::RetryNextUpdate(extracted_asset));
};
let bind_group = render_device.create_bind_group(&BindGroupDescriptor {
entries: &[
BindGroupEntry {
binding: 0,
resource: buffer.as_entire_binding(),
},
BindGroupEntry {
binding: 0,
resource: BindingResource::TextureView(texture_view),
},
BindGroupEntry {
binding: 1,
resource: BindingResource::Sampler(texture_sampler),
},
],
label: None,
layout: &material_pipeline.material_layout,
});
Ok(GpuCustomMaterial {
_buffer: buffer,
bind_group,
})
}
}
impl Material for CustomMaterial {
fn fragment_shader(asset_server: &AssetServer) -> Option<Handle<Shader>> {
Some(asset_server.load("custom_material.wgsl"))
}
fn bind_group(render_asset: &<Self as RenderAsset>::PreparedAsset) -> &BindGroup {
&render_asset.bind_group
}
fn bind_group_layout(render_device: &RenderDevice) -> BindGroupLayout {
render_device.create_bind_group_layout(&BindGroupLayoutDescriptor {
entries: &[
BindGroupLayoutEntry {
binding: 0,
visibility: ShaderStages::FRAGMENT,
ty: BindingType::Buffer {
ty: BufferBindingType::Uniform,
has_dynamic_offset: false,
min_binding_size: Some(Vec4::min_size()),
},
count: None,
},
BindGroupLayoutEntry {
binding: 1,
visibility: ShaderStages::FRAGMENT,
ty: BindingType::Texture {
multisampled: false,
sample_type: TextureSampleType::Float { filterable: true },
view_dimension: TextureViewDimension::D2Array,
},
count: None,
},
BindGroupLayoutEntry {
binding: 2,
visibility: ShaderStages::FRAGMENT,
ty: BindingType::Sampler(SamplerBindingType::Filtering),
count: None,
},
],
label: None,
})
}
}
```
### Bevy 0.8 (new)
```rust
impl Material for CustomMaterial {
fn fragment_shader() -> ShaderRef {
"custom_material.wgsl".into()
}
}
#[derive(AsBindGroup, TypeUuid, Debug, Clone)]
#[uuid = "f690fdae-d598-45ab-8225-97e2a3f056e0"]
pub struct CustomMaterial {
#[uniform(0)]
color: Color,
#[texture(1)]
#[sampler(2)]
color_texture: Handle<Image>,
}
```
## Future Work
* Add support for more binding types (cubemaps, buffers, etc). This PR intentionally includes a bare minimum number of binding types to keep "reviewability" in check.
* Consider optionally eliding binding indices using binding names. `AsBindGroup` could pass in (optional?) reflection info as a "hint".
* This would make it possible for the derive to do this:
```rust
#[derive(AsBindGroup)]
pub struct CustomMaterial {
#[uniform]
color: Color,
#[texture]
#[sampler]
color_texture: Option<Handle<Image>>,
alpha_mode: AlphaMode,
}
```
* Or this
```rust
#[derive(AsBindGroup)]
pub struct CustomMaterial {
#[binding]
color: Color,
#[binding]
color_texture: Option<Handle<Image>>,
alpha_mode: AlphaMode,
}
```
* Or even this (if we flip to "include bindings by default")
```rust
#[derive(AsBindGroup)]
pub struct CustomMaterial {
color: Color,
color_texture: Option<Handle<Image>>,
#[binding(ignore)]
alpha_mode: AlphaMode,
}
```
* If we add the option to define custom draw functions for materials (which could be done in a type-erased way), I think that would be enough to support extra non-material bindings. Worth considering!
|
||
Robert Swain
|
b333386271 |
Add reusable shader functions for transforming position/normal/tangent (#4901)
# Objective - Add reusable shader functions for transforming positions / normals / tangents between local and world / clip space for 2D and 3D so that they are done in a simple and correct way - The next step in #3969 so check there for more details. ## Solution - Add `bevy_pbr::mesh_functions` and `bevy_sprite::mesh2d_functions` shader imports - These contain `mesh_` and `mesh2d_` versions of the following functions: - `mesh_position_local_to_world` - `mesh_position_world_to_clip` - `mesh_position_local_to_clip` - `mesh_normal_local_to_world` - `mesh_tangent_local_to_world` - Use them everywhere where it is appropriate - Notably not in the sprite and UI shaders where `mesh2d_position_world_to_clip` could have been used, but including all the functions depends on the mesh binding so I chose to not use the function there - NOTE: The `mesh_` and `mesh2d_` functions are currently identical. However, if I had defined only `bevy_pbr::mesh_functions` and used that in bevy_sprite, then bevy_sprite would have a runtime dependency on bevy_pbr, which seems undesirable. I also expect that when we have a proper 2D rendering API, these functions will diverge between 2D and 3D. --- ## Changelog - Added: `bevy_pbr::mesh_functions` and `bevy_sprite::mesh2d_functions` shader imports containing `mesh_` and `mesh2d_` versions of the following functions: - `mesh_position_local_to_world` - `mesh_position_world_to_clip` - `mesh_position_local_to_clip` - `mesh_normal_local_to_world` - `mesh_tangent_local_to_world` ## Migration Guide - The `skin_tangents` function from the `bevy_pbr::skinning` shader import has been replaced with the `mesh_tangent_local_to_world` function from the `bevy_pbr::mesh_functions` shader import |
||
|
Robert Swain
|
cc4062ec43 |
Split mesh shader files (#4867)
# Objective - Split PBR and 2D mesh shaders into types and bindings to prepare the shaders to be more reusable. - See #3969 for details. I'm doing this in multiple steps to make review easier. --- ## Changelog - Changed: 2D and PBR mesh shaders are now split into types and bindings, the following shader imports are available: `bevy_pbr::mesh_view_types`, `bevy_pbr::mesh_view_bindings`, `bevy_pbr::mesh_types`, `bevy_pbr::mesh_bindings`, `bevy_sprite::mesh2d_view_types`, `bevy_sprite::mesh2d_view_bindings`, `bevy_sprite::mesh2d_types`, `bevy_sprite::mesh2d_bindings` ## Migration Guide - In shaders for 3D meshes: - `#import bevy_pbr::mesh_view_bind_group` -> `#import bevy_pbr::mesh_view_bindings` - `#import bevy_pbr::mesh_struct` -> `#import bevy_pbr::mesh_types` - NOTE: If you are using the mesh bind group at bind group index 2, you can remove those binding statements in your shader and just use `#import bevy_pbr::mesh_bindings` which itself imports the mesh types needed for the bindings. - In shaders for 2D meshes: - `#import bevy_sprite::mesh2d_view_bind_group` -> `#import bevy_sprite::mesh2d_view_bindings` - `#import bevy_sprite::mesh2d_struct` -> `#import bevy_sprite::mesh2d_types` - NOTE: If you are using the mesh2d bind group at bind group index 2, you can remove those binding statements in your shader and just use `#import bevy_sprite::mesh2d_bindings` which itself imports the mesh2d types needed for the bindings. |
||
|
Carter Anderson
|
2e79951659 |
Shader Imports. Decouple Mesh logic from PBR (#3137)
## Shader Imports
This adds "whole file" shader imports. These come in two flavors:
### Asset Path Imports
```rust
// /assets/shaders/custom.wgsl
#import "shaders/custom_material.wgsl"
[[stage(fragment)]]
fn fragment() -> [[location(0)]] vec4<f32> {
return get_color();
}
```
```rust
// /assets/shaders/custom_material.wgsl
[[block]]
struct CustomMaterial {
color: vec4<f32>;
};
[[group(1), binding(0)]]
var<uniform> material: CustomMaterial;
```
### Custom Path Imports
Enables defining custom import paths. These are intended to be used by crates to export shader functionality:
```rust
// bevy_pbr2/src/render/pbr.wgsl
#import bevy_pbr::mesh_view_bind_group
#import bevy_pbr::mesh_bind_group
[[block]]
struct StandardMaterial {
base_color: vec4<f32>;
emissive: vec4<f32>;
perceptual_roughness: f32;
metallic: f32;
reflectance: f32;
flags: u32;
};
/* rest of PBR fragment shader here */
```
```rust
impl Plugin for MeshRenderPlugin {
fn build(&self, app: &mut bevy_app::App) {
let mut shaders = app.world.get_resource_mut::<Assets<Shader>>().unwrap();
shaders.set_untracked(
MESH_BIND_GROUP_HANDLE,
Shader::from_wgsl(include_str!("mesh_bind_group.wgsl"))
.with_import_path("bevy_pbr::mesh_bind_group"),
);
shaders.set_untracked(
MESH_VIEW_BIND_GROUP_HANDLE,
Shader::from_wgsl(include_str!("mesh_view_bind_group.wgsl"))
.with_import_path("bevy_pbr::mesh_view_bind_group"),
);
```
By convention these should use rust-style module paths that start with the crate name. Ultimately we might enforce this convention.
Note that this feature implements _run time_ import resolution. Ultimately we should move the import logic into an asset preprocessor once Bevy gets support for that.
## Decouple Mesh Logic from PBR Logic via MeshRenderPlugin
This breaks out mesh rendering code from PBR material code, which improves the legibility of the code, decouples mesh logic from PBR logic, and opens the door for a future `MaterialPlugin<T: Material>` that handles all of the pipeline setup for arbitrary shader materials.
## Removed `RenderAsset<Shader>` in favor of extracting shaders into RenderPipelineCache
This simplifies the shader import implementation and removes the need to pass around `RenderAssets<Shader>`.
## RenderCommands are now fallible
This allows us to cleanly handle pipelines+shaders not being ready yet. We can abort a render command early in these cases, preventing bevy from trying to bind group / do draw calls for pipelines that couldn't be bound. This could also be used in the future for things like "components not existing on entities yet".
# Next Steps
* Investigate using Naga for "partial typed imports" (ex: `#import bevy_pbr::material::StandardMaterial`, which would import only the StandardMaterial struct)
* Implement `MaterialPlugin<T: Material>` for low-boilerplate custom material shaders
* Move shader import logic into the asset preprocessor once bevy gets support for that.
Fixes #3132
|
||
|
Carter Anderson
|
015617a774 |
Pipeline Specialization, Shader Assets, and Shader Preprocessing (#3031)
## New Features
This adds the following to the new renderer:
* **Shader Assets**
* Shaders are assets again! Users no longer need to call `include_str!` for their shaders
* Shader hot-reloading
* **Shader Defs / Shader Preprocessing**
* Shaders now support `# ifdef NAME`, `# ifndef NAME`, and `# endif` preprocessor directives
* **Bevy RenderPipelineDescriptor and RenderPipelineCache**
* Bevy now provides its own `RenderPipelineDescriptor` and the wgpu version is now exported as `RawRenderPipelineDescriptor`. This allows users to define pipelines with `Handle<Shader>` instead of needing to manually compile and reference `ShaderModules`, enables passing in shader defs to configure the shader preprocessor, makes hot reloading possible (because the descriptor can be owned and used to create new pipelines when a shader changes), and opens the doors to pipeline specialization.
* The `RenderPipelineCache` now handles compiling and re-compiling Bevy RenderPipelineDescriptors. It has internal PipelineLayout and ShaderModule caches. Users receive a `CachedPipelineId`, which can be used to look up the actual `&RenderPipeline` during rendering.
* **Pipeline Specialization**
* This enables defining per-entity-configurable pipelines that specialize on arbitrary custom keys. In practice this will involve specializing based on things like MSAA values, Shader Defs, Bind Group existence, and Vertex Layouts.
* Adds a `SpecializedPipeline` trait and `SpecializedPipelines<MyPipeline>` resource. This is a simple layer that generates Bevy RenderPipelineDescriptors based on a custom key defined for the pipeline.
* Specialized pipelines are also hot-reloadable.
* This was the result of experimentation with two different approaches:
1. **"generic immediate mode multi-key hash pipeline specialization"**
* breaks up the pipeline into multiple "identities" (the core pipeline definition, shader defs, mesh layout, bind group layout). each of these identities has its own key. looking up / compiling a specific version of a pipeline requires composing all of these keys together
* the benefit of this approach is that it works for all pipelines / the pipeline is fully identified by the keys. the multiple keys allow pre-hashing parts of the pipeline identity where possible (ex: pre compute the mesh identity for all meshes)
* the downside is that any per-entity data that informs the values of these keys could require expensive re-hashes. computing each key for each sprite tanked bevymark performance (sprites don't actually need this level of specialization yet ... but things like pbr and future sprite scenarios might).
* this is the approach rafx used last time i checked
2. **"custom key specialization"**
* Pipelines by default are not specialized
* Pipelines that need specialization implement a SpecializedPipeline trait with a custom key associated type
* This allows specialization keys to encode exactly the amount of information required (instead of needing to be a combined hash of the entire pipeline). Generally this should fit in a small number of bytes. Per-entity specialization barely registers anymore on things like bevymark. It also makes things like "shader defs" way cheaper to hash because we can use context specific bitflags instead of strings.
* Despite the extra trait, it actually generally makes pipeline definitions + lookups simpler: managing multiple keys (and making the appropriate calls to manage these keys) was way more complicated.
* I opted for custom key specialization. It performs better generally and in my opinion is better UX. Fortunately the way this is implemented also allows for custom caches as this all builds on a common abstraction: the RenderPipelineCache. The built in custom key trait is just a simple / pre-defined way to interact with the cache
## Callouts
* The SpecializedPipeline trait makes it easy to inherit pipeline configuration in custom pipelines. The changes to `custom_shader_pipelined` and the new `shader_defs_pipelined` example illustrate how much simpler it is to define custom pipelines based on the PbrPipeline.
* The shader preprocessor is currently pretty naive (it just uses regexes to process each line). Ultimately we might want to build a more custom parser for more performance + better error handling, but for now I'm happy to optimize for "easy to implement and understand".
## Next Steps
* Port compute pipelines to the new system
* Add more preprocessor directives (else, elif, import)
* More flexible vertex attribute specialization / enable cheaply specializing on specific mesh vertex layouts
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