DirectX11 Generate Input Layout from Vertex Shader using D3DReflect.

gistfile1.cpp

	
//Function Creates an input layout from the vertex shader, after compilation.
//Input layout can be reused with any vertex shaders that use the same input layout.
HRESULT CreateInputLayoutDescFromVertexShaderSignature( ID3DBlob* pShaderBlob, ID3D11Device* pD3DDevice, ID3D11InputLayout** pInputLayout, int* inputLayoutByteLength )
{
    // Reflect shader info
    ID3D11ShaderReflection* pVertexShaderReflection = nullptr;
    HRESULT hr = S_OK;
    if ( FAILED( D3DReflect( pShaderBlob->GetBufferPointer(), pShaderBlob->GetBufferSize(), IID_ID3D11ShaderReflection, (void**) &pVertexShaderReflection ) ) )
    {
        return S_FALSE;
    }
     
    // get shader description
    D3D11_SHADER_DESC shaderDesc;
    pVertexShaderReflection->GetDesc( &shaderDesc );
     
    // Read input layout description from shader info
    unsigned int byteOffset = 0;
    std::vector<D3D11_INPUT_ELEMENT_DESC> inputLayoutDesc;
    for ( unsigned int i=0; i< shaderDesc.InputParameters; ++i )
    {
        D3D11_SIGNATURE_PARAMETER_DESC paramDesc;      
        pVertexShaderReflection->GetInputParameterDesc(i, &paramDesc );
 
        // create input element desc
        D3D11_INPUT_ELEMENT_DESC elementDesc;  
        elementDesc.SemanticName = paramDesc.SemanticName;      
        elementDesc.SemanticIndex = paramDesc.SemanticIndex;
        elementDesc.InputSlot = 0;
        elementDesc.AlignedByteOffset = byteOffset;
        elementDesc.InputSlotClass = D3D11_INPUT_PER_VERTEX_DATA;
        elementDesc.InstanceDataStepRate = 0;  
 
        // determine DXGI format
        if ( paramDesc.Mask == 1 )
        {
            if ( paramDesc.ComponentType == D3D_REGISTER_COMPONENT_UINT32 ) elementDesc.Format = DXGI_FORMAT_R32_UINT;
            else if ( paramDesc.ComponentType == D3D_REGISTER_COMPONENT_SINT32 ) elementDesc.Format = DXGI_FORMAT_R32_SINT;
            else if ( paramDesc.ComponentType == D3D_REGISTER_COMPONENT_FLOAT32 ) elementDesc.Format = DXGI_FORMAT_R32_FLOAT;
            byteOffset += 4;
        }
        else if ( paramDesc.Mask <= 3 )
        {
            if ( paramDesc.ComponentType == D3D_REGISTER_COMPONENT_UINT32 ) elementDesc.Format = DXGI_FORMAT_R32G32_UINT;
            else if ( paramDesc.ComponentType == D3D_REGISTER_COMPONENT_SINT32 ) elementDesc.Format = DXGI_FORMAT_R32G32_SINT;
            else if ( paramDesc.ComponentType == D3D_REGISTER_COMPONENT_FLOAT32 ) elementDesc.Format = DXGI_FORMAT_R32G32_FLOAT;
            byteOffset += 8;
        }
        else if ( paramDesc.Mask <= 7 )
        {
            if ( paramDesc.ComponentType == D3D_REGISTER_COMPONENT_UINT32 ) elementDesc.Format = DXGI_FORMAT_R32G32B32_UINT;
            else if ( paramDesc.ComponentType == D3D_REGISTER_COMPONENT_SINT32 ) elementDesc.Format = DXGI_FORMAT_R32G32B32_SINT;
            else if ( paramDesc.ComponentType == D3D_REGISTER_COMPONENT_FLOAT32 ) elementDesc.Format = DXGI_FORMAT_R32G32B32_FLOAT;
            byteOffset += 12;
        }
        else if ( paramDesc.Mask <= 15 )
        {
            if ( paramDesc.ComponentType == D3D_REGISTER_COMPONENT_UINT32 ) elementDesc.Format = DXGI_FORMAT_R32G32B32A32_UINT;
            else if ( paramDesc.ComponentType == D3D_REGISTER_COMPONENT_SINT32 ) elementDesc.Format = DXGI_FORMAT_R32G32B32A32_SINT;
            else if ( paramDesc.ComponentType == D3D_REGISTER_COMPONENT_FLOAT32 ) elementDesc.Format = DXGI_FORMAT_R32G32B32A32_FLOAT;
            byteOffset += 16;
        }
             
        //save element desc
        inputLayoutDesc.push_back(elementDesc);
    }      
 
    // Try to create Input Layout
    hr = pD3DDevice->CreateInputLayout( &inputLayoutDesc[0], inputLayoutDesc.size(), pShaderBlob->GetBufferPointer(), pShaderBlob->GetBufferSize(), pInputLayout );
 
    //Free allocation shader reflection memory
    pVertexShaderReflection->Release();
 
    //record byte length
    *inputLayoutByteLength = byteOffset;
 
    return hr;
}

I have a question, how to know the InputSlot?In your code ,just specific it as zero,but there might be more then 1 input paramates like:

VertexOut main(float3 pos : POSITION, float4 colors : COLOR)
{
VertexOut output;
............
return output;
}
so, is there any way to know the InputSlot?