Reflect DX11 Vertex shader to create input layout

reflect_inputlayout.cpp

HRESULT CreateInputLayoutDescFromVertexShaderSignature( ID3DBlob* pShaderBlob, ID3D11Device* pD3DDevice, ID3D11InputLayout** pInputLayout )
{
    // Reflect shader info
    ID3D11ShaderReflection* pVertexShaderReflection = NULL;
    if ( FAILED( D3DReflect( pShaderBlob->GetBufferPointer(), pShaderBlob->GetBufferSize(), IID_ID3D11ShaderReflection, (void**) &pVertexShaderReflection ) ) )
    {
        return S_FALSE;
    }
 
    // Get shader info
    D3D11_SHADER_DESC shaderDesc;
    pVertexShaderReflection->GetDesc( &shaderDesc );
 
    // Read input layout description from shader info
    std::vector<D3D11_INPUT_ELEMENT_DESC> inputLayoutDesc;
    for ( uint32 i=0; i< shaderDesc.InputParameters; i++ )
    {
        D3D11_SIGNATURE_PARAMETER_DESC paramDesc;
        pVertexShaderReflection->GetInputParameterDesc(i, &paramDesc );
 
        // fill out input element desc
        D3D11_INPUT_ELEMENT_DESC elementDesc;
        elementDesc.SemanticName = paramDesc.SemanticName;
        elementDesc.SemanticIndex = paramDesc.SemanticIndex;
        elementDesc.InputSlot = 0;
        elementDesc.AlignedByteOffset = D3D11_APPEND_ALIGNED_ELEMENT;
        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;
        }
        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;
        }
        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;
        }
        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;
        }
 
        //save element desc
        inputLayoutDesc.push_back(elementDesc);
    }       
 
    // Try to create Input Layout
    HRESULT hr = pD3DDevice->CreateInputLayout( &inputLayoutDesc[0], inputLayoutDesc.size(), pShaderBlob->GetBufferPointer(), pShaderBlob->GetBufferSize(), pInputLayout );
 
    //Free allocation shader reflection memory
    pVertexShaderReflection->Release();
    return hr;
}