ShaderPermute

Simple library to generate shader permutations based on dependencies. Can also be used for text.

Current features

• Generate permutations from a json
• Generate SPIR-V code based on glsl code from the given permutations
• Post-process glsl code before compilation via lookups
• Inspect intermediate code via traverser

Installation

Use cmake fetch content

include(FetchContent)

FETCHCONTENT_DECLARE(
  permute
  URL https://github.com/MrTroble/ShaderPermute/archive/refs/heads/master.zip
)

FETCHCONTENT_MAKEAVAILABLE(permute)

target_include_directories(mytarget PUBLIC ${permute_SOURCE_DIR}/ShaderPermute ${glslang_SOURCE_DIR})
target_link_libraries(mytarget PUBLIC glslang SPIRV)

Example

if you want the integrated glsl compiler use the permute::PermuteGLSL template

auto &perm = permute::fromFile<permute::PermuteGLSL>("shader.json");

for just text with no lookups use permute::PermuteText

auto &perm = permute::fromFile<permute::PermuteText>("text.json");

loading from memory is also supported via permute::fromJson

auto &perm = permute::fromJson<PermuteText/GLSL>(js);

use the generate function to generate a permutation based on some dependencies. Keep in mind that you need to call glslang::InitializeProcess() and glslang::FinalizeProcess()

bool success = perm.generate(); // Generates SPIR-V/Text without dependencies

bool success = perm.generate({"COLOR"}) // Generates SPIR-V/Text with the COLOR dependency

Use the getter methods to retrieve the needed information afterwards

Inspect intermediate code

Create a traverser

class TestTraverser : public permute::ShaderTraverser {
public:
  bool visited = false;

  TestTraverser() : permute::ShaderTraverser() {}

  void visitSymbol(glslang::TIntermSymbol *) override { 
    visited = true; 
  }

  bool isValid(const permute::GlslSettings &settings) override {  
    return true; 
  }
};

Create a instance of the traverser before you generate your code. It will be automatically used for each generation until it is being deleted by RAII.

TestTraverser tt;
perm.generate();

Json structure

{
  "settings": { // mandatory while using glsl
    "shaderType": "vertex" // mandatory while using glsl
  },
  "codes": [
    {
      "code": [
        "$next_in vec3 POSITION;",
        "$next_out vec3 POSITIONOUT;"
      ]
    },
    {
      "code": [
        "$next_in vec4 COLOR;", // builtin lookup gives it the next input layout qualifier (or binding for ubos)
        "$next_out vec4 COLOROUT;"
      ],
      "dependsOn":  ["COLOR"]
    },
    {
      "code": [
        "$next_ublock { mat4 model; } ublock_0;",
        "$next_ublock { mat4 vp;} ublock_1;",
        "out gl_PerVertex { vec4 gl_Position; };",
        "void main() {",
        "gl_Position = ublock_1.vp * ublock_0.model * vec4(POSITION, 1);",
        "POSITIONOUT = gl_Position.xyz;"
      ]
    },
    {
      "code": [
        "COLOROUT = COLOR;"
      ],
      "dependsOn": ["COLOR"]
    },
    {
      "code": [
        "}"
      ]
    }
  ]
}