[DX12] Extract root signature binary from a shader binary created with D3DCompileFromFile.

dx12_extract_root_signature_from_shader_binary.cpp

...
	ComPtr<ID3DBlob> vertexShader = afCompileHLSL(shaderName, "VSMain", "vs_5_0");
	ComPtr<ID3DBlob> pixelShader = afCompileHLSL(shaderName, "PSMain", "ps_5_0");
	ComPtr<ID3DBlob> rootSignatureBlob;
	ComPtr<ID3D12RootSignature> rootSignature;
	if (S_OK == D3DGetBlobPart(vertexShader->GetBufferPointer(), vertexShader->GetBufferSize(), D3D_BLOB_ROOT_SIGNATURE, 0, &rootSignatureBlob))
	{
		device->CreateRootSignature(0, rootSignatureBlob->GetBufferPointer(), rootSignatureBlob->GetBufferSize(), IID_PPV_ARGS(&rootSignature));
	}
...

ComPtr<ID3DBlob> afCompileHLSL(const char* name, const char* entryPoint, const char* target)
{
	char path[MAX_PATH];
	sprintf_s(path, sizeof(path), "hlsl/%s.hlsl", name);
#ifdef _DEBUG
	UINT flags = D3DCOMPILE_ENABLE_STRICTNESS | D3DCOMPILE_DEBUG | D3DCOMPILE_SKIP_OPTIMIZATION;
#else
	UINT flags = D3DCOMPILE_ENABLE_STRICTNESS;
#endif
	ComPtr<ID3DBlob> blob, err;
	WCHAR wname[MAX_PATH];
	MultiByteToWideChar(CP_ACP, 0, path, -1, wname, dimof(wname));
	HRESULT hr = D3DCompileFromFile(wname, nullptr, nullptr, entryPoint, target, flags, 0, &blob, &err);
	if (err) {
		MessageBoxA(nullptr, (const char*)err->GetBufferPointer(), name, MB_OK | MB_ICONERROR);
	}
	return blob;
}