truespace 6

HWND tswnd;
tswnd = tsxGetMainViewHwnd();

truespace 7.6

HRESULT hr;
HWND tswnd;
// get Window manager package
CComPtr spKernelPackage;
hr = CRpExamplesPlugin::GetKernelPackage(&spKernelPackage);
if (FAILED(hr))
   return hr;
CComPtr spPackage;
hr = spKernelPackage->FindPackage(DEF_GUIDNAME(CRpWinMng), &spPackage);
if (FAILED(hr))
   return hr;
CComQIPtr spWinPackage = spPackage;
// get windows manager node
CComPtr spWinMgrNode;
hr = spWinPackage->GetWindowsManagerNode(&spWinMgrNode);
if (FAILED(hr))
   return hr;
CComQIPtr spWinMng = spWinMgrNode;
spWinMng->get_MainWindowHandle(&tswnd);