Question Injecting Different Varients into a Shader at Runtime

I am trying to get a very basic implementation of IUnityShaderCompilerAccess.h to work so I can inject different variants into a shader from a DLL but the little documentation provided is vague and there are no examples on the internet on how to do this.

The manual says:

The code of interest (found within Unity\Editor\Data\PluginAPI\IUnityShaderCompilerAccess.h):

Code (CSharp):

1. enum UnityShaderCompilerExtEventType
2. {
3.     kUnityShaderCompilerExtEventCreateCustomSourceVariant, // The plugin can create a new variant based on the initial snippet. The callback will receive UnityShaderCompilerExtCustomSourceVariantParams as data.
4.  
5.     ...
6.  
7. };
8.  
9.  
10. struct UnityShaderCompilerExtCustomSourceVariantParams
11. {
12.     char* outputSnippet;                                    // snippet after the plugin has finished processing it.
13.     char* outputKeywords;                                   // keywords exported by the plugin for this specific variant
14.     const char* inputSnippet;                               // the source shader snippet
15.     bool vr;                                                // is VR enabled / supported ?
16.     UnityShaderCompilerExtCompilerPlatform platform;        // compiler platform
17.     UnityShaderCompilerExtShaderType shaderType;            // source code type
18. };

and the brief example:

Code (CSharp):

1. extern "C" void UNITY_INTERFACE_EXPORT UNITY_INTERFACE_API
2.         UnityShaderCompilerExtEvent(UnityShaderCompilerExtEventType event, void* data)
3.         {
4.             switch (event)
5.             {
6.  
7.                 ...
8.  
9.                 case kUnityShaderCompilerExtEventPluginConfigure:
10.                 {
11.                     unsigned int GPUCompilerMask = (1 << kUnityShaderCompilerExtGPUProgramTargetDX11VertexSM40)
12.                     | (1 << kUnityShaderCompilerExtGPUProgramTargetDX11VertexSM50)
13.                     | (1 << kUnityShaderCompilerExtGPUProgramTargetDX11PixelSM40)
14.                     | (1 << kUnityShaderCompilerExtGPUProgramTargetDX11PixelSM50)
15.                     | (1 << kUnityShaderCompilerExtGPUProgramTargetDX11GeometrySM40)
16.                     | (1 << kUnityShaderCompilerExtGPUProgramTargetDX11GeometrySM50)
17.                     | (1 << kUnityShaderCompilerExtGPUProgramTargetDX11HullSM50)
18.                     | (1 << kUnityShaderCompilerExtGPUProgramTargetDX11DomainSM50);
19.  
20.                     unsigned int ShaderMask = kUnityShaderCompilerExtGPUProgramVS | kUnityShaderCompilerExtGPUProgramDS;
21.  
22.                     IUnityShaderCompilerExtPluginConfigure* pluginConfig = (IUnityShaderCompilerExtPluginConfigure*)data;
23.                     pluginConfig->ReserveKeyword(SHADER_KEYWORDS);
24.                     pluginConfig->SetGPUProgramCompilerMask(GPUCompilerMask);
25.                     pluginConfig->SetShaderProgramMask(ShaderMask);
26.                     break;
27.                 }
28.             }
29.         }

It is unclear how we are supposed to tell the plugin which shader we are referring to (because the callback only receives an input "snippet" of shader code rather than the whole shader with the name attached).

 

Bumping as I'd like to know as well