fungt-dialect

MLIR dialect for shader compilation, lowering to SPIR-V for use in OpenGL and Vulkan.

Status

fungt-dialect is a working shader compiler. A user writes a .fgt shader file, runs three commands, and gets a validated .spv binary ready to load into OpenGL or Vulkan. Confirmed rendering on both Intel Arc and NVIDIA hardware.

Pipeline

shader.fgt
        |
   fungt-parse --shader shader.fgt | fungt-opt --fungt-shader-lower-to-spirv - -o lowered.mlir
        |
   fungt-translate --fungt-to-spirv lowered.mlir -o shader.spv
        |
   OpenGL: glShaderBinary + glSpecializeShader (GL_ARB_gl_spirv)
   Vulkan: vkCreateShaderModule

Surface Syntax

Users write .fgt files directly. No MLIR knowledge required.

Fragment shader reading from a uniform and writing to an output:

fragment_shader {
    uniform tint set(0) binding(0) : vec4
    color = load(tint)
    out color location(0)
}

Vertex shader passing an input through to an output:

vertex_shader {
    in position location(0) : vec4
    out gl_position location(0) : vec4
    gl_position = position
}

Supported statements inside a shader block:

uniform name set(N) binding(N) : type declares a uniform buffer binding.

in name location(N) : type reads from a vertex attribute or varying input.

out name location(N) writes a named value to a shader output.

name = load(binding) loads the value from a named uniform binding.

name = expression assigns the result of an expression to a variable.

Supported types: vec4

Comments use //.

Ops

fungt.shader_entry Declares a shader entry point with an execution model of "Vertex" or "Fragment".

fungt.shader_end Terminates a shader entry body.

fungt.const_vec4 Constant 4-component float vector.

fungt.input Reads from a location decorated shader input.

fungt.output Writes to a location decorated shader output.

fungt.resource_binding Declares a named resource at a descriptor set and binding index. Storage class must be "Uniform", "StorageBuffer", or "UniformConstant".

fungt.load_resource Reads the value from a named resource binding.

Tools

fungt-parse Reads a .fgt file and emits fungt-dialect MLIR. Use --shader flag for shader files.

fungt-opt Runs lowering passes. --fungt-shader-lower-to-spirv lowers fungt shader ops to spirv dialect MLIR. Text in, text out.

fungt-translate Serializes spirv dialect MLIR to a binary .spv file. Text in, binary out.

OpenGL Note

Both vertex and fragment shaders in a single OpenGL program must be SPIR-V modules. Mixing GLSL and SPIR-V shaders in the same program produces GL_INVALID_OPERATION on link, and causes a driver level segmentation fault in Mesa on Intel Arc hardware.

Building

Requires an LLVM/MLIR build. Point CMake at your MLIR install:

mkdir build && cd build
cmake -G Ninja .. \
  -DMLIR_DIR=/path/to/llvm-project/build/lib/cmake/mlir \
  -DLLVM_EXTERNAL_LIT=/path/to/llvm-project/build/bin/llvm-lit
ninja

Prior Work

fungt-dialect originally targeted GLCompute execution mode SPIR-V for LLM generated particle physics kernels. That work has been superseded by the shading language direction above and is no longer the project's purpose.

Part of FunGT

https://github.com/FunGTs/FunGT

License

Apache 2.0 with LLVM Exceptions. See LICENSE for details.