121 lines
7.5 KiB
Markdown
121 lines
7.5 KiB
Markdown
# librashader
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<small>*Mega Bezel SMOOTH-ADV on OpenGL 4.6*</small>
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librashader (*/ˈli:brəʃeɪdɚ/*) is a preprocessor, compiler, and runtime for RetroArch 'slang' shaders, rewritten in pure Rust.
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[](https://crates.io/crates/librashader) [](https://docs.rs/librashader) 
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## Supported Render APIs
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librashader supports OpenGL 3, OpenGL 4.6, Vulkan, DirectX 11, and DirectX 12. Older versions
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of DirectX and OpenGL, as well as Metal, are not supported (but pull-requests are welcome).
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| **API** | **Status** | **`librashader` feature** |
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|-------------|------------|---------------------------|
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| OpenGL 3.3+ | ✔ | `gl` |
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| OpenGL 4.6 | ✔ | `gl` |
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| Vulkan 1.3+ | ✔ | `vk` |
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| Direct3D11 | ✔ | `d3d11` |
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| Direct3D12 | 🚧 | `d3d12` |
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| OpenGL 2 | ❌ | |
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| DirectX 9 | ❌ | |
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| Metal | ❌ | |
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✔ = Render API is supported — 🚧 = Support is in progress — ❌ Render API is not supported
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## Usage
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🚧 *`librashader_ld` is WIP* 🚧
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librashader provides both a Rust API under the `librashader` crate, and a C API. Both APIs are first-class, fully supported.
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The librashader C API is best used by linking statically with `librashader_ld`, which implements a loader that dynamically
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loads the librashader (`librashader.so` or `librashader.dll`) implementation in the search path. You may also link against
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`librashader_capi` directly with [`librashader.h`](https://github.com/SnowflakePowered/librashader/blob/master/include/librashader.h).
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The C API currently does not expose the [shader reflection API](https://docs.rs/librashader/latest/librashader/reflect/index.html). Work
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is in progress to expose this to C. In the meanwhile, if you wish to implement a custom runtime for librashader, it will have to be done
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in Rust.
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### C ABI Compatibility
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The recommended way of integrating `librashader` is by the `librashader_ld` single header library, ABI stability
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is important to ensure that updates to librashader do not break existing consumers.
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Pre-1.0, nothing is guaranteed to be stable, but the following APIs are unlikely to change their ABI unless otherwise indicated.
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* `libra_preset_*`
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* `libra_error_*`
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The following APIs, mostly runtime, are more likely to change their ABI before a 1.0 release as I experiment with what
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works best.
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* `libra_gl_*`
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* `libra_vk_*`
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* `libra_d3d11_*`
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* `libra_d3d12_*`
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If you do not mind linking against `librashader_capi` directly, [`librashader.h`](https://github.com/SnowflakePowered/librashader/blob/master/include/librashader.h)
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is unlikely to break API stability.
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## Compatibility
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librashader implements the entire RetroArch shader pipeline and is highly compatible with existing shaders,
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but there are some deliberate differences in design choices that may potentially cause incompatiblities with certain
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shaders.
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Please report an issue if you run into a shader that works in RetroArch, but not under librashader.
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* Variables can only be bound in *either* the UBO or push constant block.
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* RetroArch allows a variable to be present in both a push constant block and a UBO block at the same time. To make the
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implementation a little cleaner, librashader only allows a variable to be in *either* a push constant block or a UBO
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block. As far as I have tested, there are no shaders in [libretro/slang-shaders](https://github.com/libretro/slang-shaders)
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that bind the same variable in both the push constant and the UBO block.
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* Filter chains do not terminate at the backbuffer.
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* Unlike RetroArch, librashader does not have full knowledge of the entire rendering state and is designed to be pluggable
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at any point in your render pipeline. Instead, filter chains terminate at a caller-provided output surface and viewport.
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It is the caller's responsibility to blit the surface back to the backbuffer.
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* Runtime-specific differences
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* OpenGL
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* Copying of in-flight framebuffer contents to history is done via `glBlitFramebuffer` rather than drawing a quad into an intermediate FBO.
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* Sampler objects are used rather than `glTexParameter`.
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* Sampler inputs and outputs are not renamed. This is useful for debugging shaders in RenderDoc.
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* UBO and Push Constant Buffer sizes are padded to 16-byte boundaries.
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* OpenGL 4.6+
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* All caveats from the OpenGL 3.3+ section should be considered.
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* 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.
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* 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.
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* Direct3D 11
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* Framebuffer copies are done via `ID3D11DeviceContext::CopySubresourceRegion` rather than a CPU conversion + copy.
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* HDR10 support is not part of the shader runtime and is not supported.
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* Vulkan 1.3+
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* The Vulkan runtime uses [`VK_KHR_dynamic_rendering`](https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VK_KHR_dynamic_rendering.html). This extension must be enabled at device creation to use librashader.
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* UBOs use multiple discontiguous buffers. This may be improved in the future by switching to VMA rather than manually handling allocations.
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Most, if not all shader presets should work fine on librashader. The runtime specific differences should not affect the output,
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and are more a heads-up for integrating librashader into your project.
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Compatibility issues may arise with framebuffer copies for original history, but I have not found any yet;
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if it does end up that this results in actual rendering differences I may change the implementation to be more in line
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with RetroArch's copy implementation. However, since the Vulkan runtime already uses `vkCmdCopyImage` it is likely that it will
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not cause issues.
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## License
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The core parts of librashader such as the preprocessor, the preset parser,
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the reflection library, and the runtimes, are all licensed under the Mozilla Public License version 2.0.
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The librashader C API, i.e. its headers and definitions, *not its implementation in `librashader_capi`*,
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are more permissively licensed, and may allow you to use librashader in your permissively
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licensed or proprietary project.
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To facilitate easier use of librashader in projects incompatible with MPL-2.0, `librashader_ld`
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implements a loader which thunks its calls to any `librashader.so` or `librashader.dll`
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library found in the load path. A non-MPL-2.0 compatible project may link against
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`librashader_ld` to use the librashader runtime, *provided that `librashader.so` or `librashader.dll`
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are distributed under the restrictions of MPLv2*.
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Note that this means that if your project is not compatible with MPL-2.0, you **can not distribute `librashader.so` or `librashader.dll`**
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alongside your project. The end user must obtain the implementation of librashader themselves.
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At your discretion, you may instead choose to distribute `librashader` under the terms of GPLv3 rather than MPL-2.0 |