Spirv passthrough main (adopted, part deux) (#15352)

**Note:** This is an adoption of @Shfty 's adoption (#8131) of #3996!
All I've done is updated the branch and run the docs CI.

> **Note:** This is an adoption of #3996, originally authored by
@molikto
> 
> # Objective
> Allow use of `wgpu::Features::SPIRV_SHADER_PASSTHROUGH` and the
corresponding `wgpu::Device::create_shader_module_spirv` for SPIR-V
shader assets.
> 
> This enables use-cases where naga is not sufficient to load a given
(valid) SPIR-V module, i.e. cases where naga lacks support for a given
SPIR-V feature employed by a third-party codegen backend like
`rust-gpu`.
> 
> ## Solution
> * Reimplemented the changes from [Spirv shader
bypass #3996](#3996), on account
of the original branch having been deleted.
> * Documented the new `spirv_shader_passthrough` feature flag with the
appropriate platform support context from [wgpu's
documentation](https://docs.rs/wgpu/latest/wgpu/struct.Features.html#associatedconstant.SPIRV_SHADER_PASSTHROUGH).
> 
> ## Changelog
> * Adds a `spirv_shader_passthrough` feature flag to the following
crates:
>   
>   * `bevy`
>   * `bevy_internal`
>   * `bevy_render`
> * Extends `RenderDevice::create_shader_module` with a conditional call
to `wgpu::Device::create_shader_module_spirv` if
`spirv_shader_passthrough` is enabled and
`wgpu::Features::SPIRV_SHADER_PASSTHROUGH` is present for the current
platform.
> * Documents the relevant `wgpu` platform support in
`docs/cargo_features.md`

---------

Co-authored-by: Josh Palmer <1253239+Shfty@users.noreply.github.com>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>

Cargo.toml

@@ -164,6 +164,9 @@ bevy_gizmos = ["bevy_internal/bevy_gizmos", "bevy_color"]
 # Provides a collection of developer tools
 bevy_dev_tools = ["bevy_internal/bevy_dev_tools"]
 
+# Enable passthrough loading for SPIR-V shaders (Only supported on Vulkan, shader capabilities and extensions must agree with the platform implementation)
+spirv_shader_passthrough = ["bevy_internal/spirv_shader_passthrough"]
+
 # Tracing support, saving a file in Chrome Tracing format
 trace_chrome = ["trace", "bevy_internal/trace_chrome"]
 

crates/bevy_internal/Cargo.toml

@@ -44,6 +44,9 @@ ktx2 = ["bevy_render/ktx2"]
 zlib = ["bevy_render/zlib"]
 zstd = ["bevy_render/zstd"]
 
+# Enable SPIR-V passthrough
+spirv_shader_passthrough = ["bevy_render/spirv_shader_passthrough"]
+
 # Include tonemapping LUT KTX2 files.
 tonemapping_luts = ["bevy_core_pipeline/tonemapping_luts"]
 

crates/bevy_render/Cargo.toml

@@ -27,6 +27,9 @@ shader_format_spirv = ["wgpu/spirv", "naga/spv-in", "naga/spv-out"]
 zlib = ["flate2"]
 zstd = ["ruzstd"]
 
+# Enable SPIR-V shader passthrough
+spirv_shader_passthrough = []
+
 trace = ["profiling"]
 tracing-tracy = []
 ci_limits = []

crates/bevy_render/src/renderer/render_device.rs

@@ -49,6 +49,28 @@ impl RenderDevice {
     /// Creates a [`ShaderModule`](wgpu::ShaderModule) from either SPIR-V or WGSL source code.
     #[inline]
     pub fn create_shader_module(&self, desc: wgpu::ShaderModuleDescriptor) -> wgpu::ShaderModule {
+        #[cfg(feature = "spirv_shader_passthrough")]
+        match &desc.source {
+            wgpu::ShaderSource::SpirV(source)
+                if self
+                    .features()
+                    .contains(wgpu::Features::SPIRV_SHADER_PASSTHROUGH) =>
+            {
+                // SAFETY:
+                // This call passes binary data to the backend as-is and can potentially result in a driver crash or bogus behaviour.
+                // No attempt is made to ensure that data is valid SPIR-V.
+                unsafe {
+                    self.device
+                        .create_shader_module_spirv(&wgpu::ShaderModuleDescriptorSpirV {
+                            label: desc.label,
+                            source: source.clone(),
+                        })
+                }
+            }
+            _ => self.device.create_shader_module(desc),
+        }
+
+        #[cfg(not(feature = "spirv_shader_passthrough"))]
         self.device.create_shader_module(desc)
     }
 

docs/cargo_features.md

@@ -78,6 +78,7 @@ The default feature set enables most of the expected features of a game engine,
 |serialize|Enable serialization support through serde|
 |shader_format_glsl|Enable support for shaders in GLSL|
 |shader_format_spirv|Enable support for shaders in SPIR-V|
+|spirv_shader_passthrough|Enable passthrough loading for SPIR-V shaders (Only supported on Vulkan, shader capabilities and extensions must agree with the platform implementation)|
 |symphonia-aac|AAC audio format support (through symphonia)|
 |symphonia-all|AAC, FLAC, MP3, MP4, OGG/VORBIS, and WAV audio formats support (through symphonia)|
 |symphonia-flac|FLAC audio format support (through symphonia)|