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librashader (/ˈli:brəʃeɪdɚ/) is a preprocessor, compiler, and runtime for RetroArch 'slang' shaders, rewritten in pure Rust.
For end-users, librashader is available from the Open Build Service for a variety of Linux distributions and platforms. Windows and macOS users can grab the latest binaries from GitHub Releases.
librashader supports all modern graphics runtimes, including wgpu, Vulkan, OpenGL 3.3+ and 4.6 (with DSA), Direct3D 11, Direct3D 12, and Metal.
librashader does not support legacy render APIs such as older versions of OpenGL or Direct3D, except for limited support for Direct3D 9.
API | Status | librashader feature |
---|---|---|
OpenGL 3.3+ | ✅ | gl |
OpenGL 4.6 | ✅ | gl |
Vulkan | ✅ | vk |
Direct3D 9 | 🆗️ | d3d9 |
Direct3D 11 | ✅ | d3d11 |
Direct3D 12 | ✅ | d3d12 |
Metal | ✅ | metal |
wgpu | 🆗 | wgpu |
✅ Full Support — 🆗 Secondary Support
Shader compatibility is not guaranteed on render APIs with secondary support.
wgpu has restrictions on shaders that can not be converted to WGSL, such as those that use inverse
. Direct3D 9 does not support
shaders that need Direct3D 10+ only features, or shaders that can not be compiled to Shader Model 3.0.
librashader provides both a Rust API under the librashader
crate, and a C API. Both APIs are first-class and fully supported.
The C API is geared more towards integration with existing projects. The Rust librashader
crate exposes more
of the internals if you wish to use parts of librashader piecemeal.
The librashader C API is best used by including librashader_ld.h
in your project, which implements a loader that dynamically
loads the librashader (librashader.so
, librashader.dll
, or librashader.dylib
) implementation in the search path.
The recommended way of integrating librashader
is by the librashader_ld
single header library which implements
a dynamic loader for librashader.dll
/ librashader.so
/ librashader.dylib
. See the versioning policy
for details on how librashader handles C ABI and API stability with regards to library updates. You can also link dynamically
with just librashader.h
and the equivalent of -lrashader
.
Linking statically against librashader.h
is possible, but is not officially supported. You will need to ensure
linkage parameters are correct in order to successfully link with librashader.lib
or librashader.a
.
The corrosion CMake package is highly recommended.
Except for the Metal runtime, in general, it is safe to create a filter chain instance from a different thread, but drawing frames requires external synchronization of the filter chain object.
Filter chains can be created from any thread, but requires external synchronization of the graphics device queue where applicable
(in Direct3D 11, the immediate context is considered the graphics device queue), as loading LUTs requires command submission to the GPU.
Initialization of GPU resources may be deferred asynchronously using the filter_chain_create_deferred
functions, but the caller is responsible for
submitting the recorded commands to the graphics device queue, and ensuring that the work is complete before drawing shader pass frames.
OpenGL has an additional restriction where creating the filter chain instance in a different thread is safe if and only if the thread local OpenGL context is initialized to the same context as the drawing thread. Support for deferral of GPU resource initialization is not available to OpenGL.
The Metal runtime is not thread safe. However you can still defer submission of GPU resource initialization through the
filter_chain_create_deferred
function.
The Direct3D 9 API is not thread safe, unless D3DCREATE_MULTITHREADED
is enabled at device creation.
All runtimes render intermediate passes with an identity matrix MVP and a VBO for with range [-1, 1]
. The final pass uses a
Quad VBO with range [0, 1]
and the following projection matrix by default.
static DEFAULT_MVP: &[f32; 16] = &[
2.0, 0.0, 0.0, 0.0,
0.0, 2.0, 0.0, 0.0,
0.0, 0.0, 0.0, 0.0,
-1.0, -1.0, 0.0, 1.0,
];
As with RetroArch, a rotation on this MVP will be applied only on the final pass for these runtimes. This is the only way to pass orientation information to shaders.
If you wish to contribute a runtime implementation not already available, see the librashader-runtime crate for helpers and shared logic used across all librashader runtime implementations. Using these helpers and traits will ensure that your runtime has consistent behaviour for uniform and texture semantics bindings with the existing librashader runtimes.
These types should not be exposed to the end user in the runtime's public API, and should be kept internal to the implementation of the runtime.
librashader provides a command-line interface to reflect and debug 'slang' shaders and presets.
Usage: librashader-cli <COMMAND>
Commands:
render Render a shader preset against an image
compare Compare two runtimes and get a similarity score between the two runtimes rendering the same frame
parse Parse a preset and get a JSON representation of the data
pack Create a serialized preset pack from a shader preset
preprocess Get the raw GLSL output of a preprocessed shader
transpile Transpile a shader in a given preset to the given format
reflect Reflect the shader relative to a preset, giving information about semantics used in a slang shader
help Print this message or the help of the given subcommand(s)
Options:
-h, --help Print help
-V, --version Print version
For more information, see CLI.md
.
For Rust projects, simply add the crate to your Cargo.toml
.
cargo add librashader
To build the C compatible dynamic library, run the build script.
cargo run -p librashader-build-script -- --profile optimized
This will output a librashader.dll
or librashader.so
in the target folder. Profile can be debug
, release
, or
optimized
for full LTO.
While librashader has no build-time dependencies, using librashader_ld.h
may require headers from
the relevant runtime graphics API.
While librashader is intended to be used with nightly Rust until required features are stabilized, it supports being
built with stable Rust with the stable
feature.
librashader = { features = ["stable"] }
If building the C API, the --stable
flag in the build script will enable the stable
feature.
cargo +stable run -p librashader-build-script -- --profile optimized --stable
There are some caveats when building against stable Rust, such that building librashader against nightly Rust is still highly encouraged.
- C headers will not be regenerated when building with the
stable
feature. - There is a minor performance hit in initial shader compilation when building against stable Rust. This is due to boxed trait objects being used instead of
impl Trait
. - A higher MSRV is required when building against stable Rust.
When the trait_alias_impl_trait
feature is stabilized, the stable
feature will be removed.
The following Rust examples show how to use each librashader runtime.
Some basic examples on using the C API are also provided.
librashader implements the entire RetroArch shader pipeline and is highly compatible with existing shaders.
Please report an issue if you run into a shader that works in RetroArch, but not under librashader.
- Filter chains do not terminate at the backbuffer.
- Unlike RetroArch, librashader does not have full knowledge of the entire rendering state and is designed to be pluggable at any point in your render pipeline. Instead, filter chains terminate at a caller-provided output surface and viewport. It is the caller's responsibility to blit the surface back to the backbuffer.
- Shaders are compiled in parallel where possible. This should noticeably decrease preset compile times. Parallel shader compilation is not available to OpenGL.
- HDR10 support is not part of any shader runtime and is not supported by librashader.
- For performance reasons, mipmaps are never generated for the input texture. In theory, this means that
presets with
mipmap_input0 = "true"
will not get a mipmapped input. In practice, no known shader presets setmipmap_input0 = "true"
. - The preset parser is a substantially stricter implementation that the one in RetroArch. Not all shader presets may be compatible. If you find this is the case, please file an issue so a workaround can be added.
- Shaders are pre-linked at the SPIR-V level before being passed to the driver. Unused inputs in the fragment shader are removed, and the corresponding input in the vertex shader is downgraded to a global variable.
- OpenGL
- Copying of in-flight framebuffer contents to history is done via
glBlitFramebuffer
rather than drawing a quad into an intermediate FBO. - Sampler objects are used rather than
glTexParameter
. - Sampler inputs and outputs are not renamed. This is useful for debugging shaders in RenderDoc.
- UBO and Push Constant Buffer sizes are padded to 16-byte boundaries.
- The OpenGL runtime uses the same VBOs as the other runtimes as well as the identity matrix MVP for intermediate passes. RetroArch's OpenGL driver uses only the final VBO.
- Copying of in-flight framebuffer contents to history is done via
- OpenGL 4.6+
- All caveats from the OpenGL 3.3+ section should be considered.
- Should work on OpenGL 4.5 but this is not guaranteed. The OpenGL 4.6 runtime may eventually switch to using
ARB_spirv_extensions
for loading shaders, and this will not be marked as a breaking change. - The OpenGL 4.6 runtime uses Direct State Access to minimize changes to the OpenGL state. For GPUs released within the last 5 years, this may improve performance.
- The OpenGL runtime uses the same VBOs as the other runtimes as well as the identity matrix MVP for intermediate passes. RetroArch's OpenGL driver uses only the final VBO.
- Vulkan
- The Vulkan runtime can use
VK_KHR_dynamic_rendering
. This extension must be enabled at device creation. Dynamic rendering may have improved performance when enabled, and supported by the host hardware. - Allocations within the runtime are done through gpu-allocator rather than handled manually.
- The Vulkan runtime can use
- Direct3D 11
- Framebuffer copies are done via
ID3D11DeviceContext::CopySubresourceRegion
rather than a CPU conversion + copy.
- Framebuffer copies are done via
- Direct3D 12
- The Direct3D 12 runtime uses render passes. This feature has been available since Windows 10 version 1809, which was released in late 2018.
- For maximum compatibility with shaders, a shader compile pipeline based on
spirv-to-dxil
is used, with the SPIRV-Cross HLSL pipeline used as a fallback. This brings shader compatibility beyond what the RetroArch Direct3D 12 driver provides. The HLSL pipeline fallback may be removed in the future asspirv-to-dxil
improves. - The Direct3D 12 runtime requires
dxcompiler.dll
from the DirectX Shader Compiler, which may already be installed as part of Direct3D12.dxil.dll
is not required.
- Metal
- The Metal runtime uses the same VBOs as the other runtimes as well as the identity matrix MVP for intermediate passes. RetroArch's Metal driver uses only the final VBO.
Most, if not all shader presets should work fine on librashader. The runtime specific differences should not affect the output, and are more a heads-up for integrating librashader into your project.
librashader typically follows Semantic Versioning with respect to the Rust API, where a minor version
number bump indicates a 'breaking change' during 0.x.y
, and a non-'breaking change' after 1.x.y
. However, a
"breaking change" that results in a version number bump does not correspond to a break in the C API after version 0.1.0.
The C API is instead versioned separately with two monotonically increasing version numbers exported to the librashader C headers
LIBRASHADER_CURRENT_VERSION
specifies the API version exported by the librashader implementation.LIBRASHADER_CURRENT_ABI
specifies the ABI version exported by the librashader implementation.
An increase in LIBRASHADER_CURRENT_VERSION
is guaranteed to be backwards compatible for the same LIBRASHADER_CURRENT_ABI
.
It somewhat corresponds to a "minor" version in semantic versioning terminology, except that it is always monotonically increasing.
Backwards-compatible additions to the C API will result in an increase to LIBRASHADER_CURRENT_VERSION
.
APIs introduced after a certain LIBRASHADER_CURRENT_VERSION
may or may not be available to prior versions. In particular, new features enabled by
filter or frame option structs require LIBRASHADER_CURRENT_VERSION
be the greater than or equal to the version in which the option was
introduced, or a default value will be passed, which may or may not enable the feature depending on backwards compatibility for
that particular feature.
Any change to LIBRASHADER_CURRENT_ABI
indicates a breaking change for the C ABI. For safety reasons, librashader_ld.h
will check to ensure that LIBRASHADER_CURRENT_ABI
matches that of the loaded librashader binary. If it does not match,
librashader will not load. A value of 0
for LIBRASHADER_CURRENT_ABI
indicates the "null" instance where every operation
is a no-op, which occurs if no compatible librashader implementation could be found.
The SONAME
of librashader.so
when installed via package manager is set to LIBRASHADER_CURRENT_ABI
.
The above does not apply to releases of librashader prior to 0.1.0
, which were allowed to break API and ABI compatibility
in both the Rust and C API without an increase to either LIBRASHADER_CURRENT_VERSION
or LIBRASHADER_CURRENT_ABI
.
The ABI version was bumped from 1
to 2
with librashader 0.5.0
. See MIGRATION-ABI2.md
for migration instructions.
Building against stable Rust requires the following MSRV.
- All platforms: 1.78
When building against nightly Rust, the following MSRV policy is enforced for unstable library features.
- All platforms: 1.78
A CI job runs weekly to ensure librashader continues to build on nightly.
Note that the MSRV is only intended to ease distribution on Linux when building against nightly Rust or with RUSTC_BOOTSTRAP=1
, and is allowed to change any time.
It generally tracks the latest version of Rust available in the latest version of Ubuntu, but this may change with no warning in a patch release.
The core parts of librashader such as the preprocessor, the preset parser, the reflection library, and the runtimes, are all licensed under the Mozilla Public License version 2.0.
The librashader C API, i.e. its headers and definitions, not its implementation in librashader-capi
,
are more permissively licensed, and may allow you to use librashader in your permissively
licensed or proprietary project.
To facilitate easier use of librashader in projects incompatible with MPL-2.0, librashader_ld
implements a loader which thunks its calls to any librashader.so
, librashader.dll
, or librashader.dylib
.
library found in the load path. A non-MPL-2.0 compatible project may link against
librashader_ld
to use the librashader runtime, provided that librashader.so
, librashader.dll
or librashader.dylib
are distributed under the restrictions of MPLv2.
Note that this means that if your project is unable to comply with the requirements of MPL-2.0,
you can not distribute librashader.so
, librashader.dll
or librashader.dylib
alongside your project.
The end user must obtain the implementation of librashader themselves. For more information,
see the MPL 2.0 FAQ.
At your discretion, you may instead choose to distribute librashader
under the terms of GPLv3 rather than MPL-2.0.