DirectXShaderCompiler VS SPIRV-Cross

> We may support DXBC generation in Clang in the future (we mentioned that in the original proposal to LLVM). That work is unlikely to begin for a few years as our focus will be on supporting DXIL and SPIR-V generation first.

I appreciate this quote[0] from the microsoft camp. Setting clear expectations that something will not be done is a nice bit of fresh air.

[0] https://github.com/microsoft/DirectXShaderCompiler/issues/57...

There's no need for transpilers these days, you can just compile HLSL to SPIR-V bytecode with dxc.

https://github.com/microsoft/DirectXShaderCompiler

Use DXC and only HLSL for your main shader editing.

You can see libdxilconv in there, DXIL is the DirectX Intermediate Representation, documented in the open source shader compiler from Microsoft.

BTW, this problem can be reproduced as described below: - clone https://github.com/SaschaWillems/Vulkan.git - build the project and run it with arguments : -v - s hlsl to enable the validation layer and to use hlsl code - run ComputeShader project. The following validation error "Type mismatch on descriptor slot ..." will be shown in the console. - to fix it, as suggested above, you can replace the 3rd line of emboss.comp, sharpen.comp, and edgedetect.comp from: Texture2D inputImage : register(t0); //Creates validation errors to RWTexture2D inputImage : register(u0); //no validation errors (you'll then need to recompile the shaders to spv with a proper hlsl compiler such as Microsoft dxc)

EDIT: There is also naga but it does not take HLSL as input: https://github.com/gfx-rs/naga but you can use DirectXShaderCompiler to compile to SpirV, then use naga to compile to Metal.

🤨 For a "refusal to acknowledge it", they do appear to have a rather sizeable document mapping between HLSL and SPIR-V? https://github.com/microsoft/DirectXShaderCompiler/blob/main/docs/SPIR-V.rst

I am starting work on a compute-driven rendering engine, and it seems that the best way to go around it will be to write code in HSSL, and then use DirectXShaderCompiler to generate SPIR-V, and SPIRV-Cross to then generate MSL. And while DXSC's repo has a page on incompatibilities, no such resource seems to exist for SPIRV-Cross targeting Metal.

DirectX Shader Compiler

There also exists something like SPIRV-Cross which promises to be able to generate code from the SPIRV intermediate representation into Metal and all versions of GLSL and HLSL. I am not sure really how good it is at this point, but going forward we might start to see more high-level shader languages, that compile to SPRIV and then from there to the myriad of different shader formats different platforms expect.

If you have shaders, I believe you can use SPIRV-Cross to generate GLSL, which you can probably get to pass as OpenCL C with just a bunch of macro tweaks, or at worst some small changes to spv-cross.

Regarding reflection, here is a guide: https://github.com/KhronosGroup/SPIRV-Cross/wiki/Reflection-API-user-guide

I am working on an engine that targets Vulkan and Metal. I'm at the point now where I want to be able to dynamically update my shader at runtime to suit the type of data being sent in for drawing. I am currently using offline compilation for my GLSL (for Vulkan) and MSL (for Metal) shaders. What are your workflows for situations like this? For those using tools like SPIR-V Cross and shaderc, what has your experience been with these tools keeping up to date with the latest features in the specs?

For cross-platform support look at WebGPU and Vulkan (e.g,: [0] [1]. Essentially, you would need to write the func in WGSL or GLSL, HLSL or MSL. Each of these can be cross-compiled to SPIR-V (what Vulkan needs) with cross-compilers such as spirv-cross and naga.

Just for reference, the library I'm using (both for compiling the shaders and for reflection), is SPIRV-Cross by the Khronos Group and here you have the docs for the reflection API. I wanted to check out `glslang` but honestly this one so far has worked like a charm.

Aside from SPIRV-Reflect, if you're using SPIRV-cross to cross compile your shaders, there is also a --reflect arg you can pass which spits out reflection info in JSON format. We already need to cross compile from spirv, so it just removes a tool in the chain to depend on.

For your own engine, use the format your API uses. If you need crossplatformness, there is a new path available. Write your shaders in a language that compiles to SPIR-V (HLSL/GLSL are the most obvious languages), and then use SPIR-V Cross to compile the SPIR-V back to HLSL/GLSL for other API to consume.