If you have to exchange data with other applications via IGES or STEP (or perhaps other formats, if you are a commercial client of the Open CASCADE company), you might want to enrich your application with meta data in addition to geometry. We will consider names and colors which are often asked about on the Open CASCADE forum.

OCC provides a ready-to-use framework – called XDE (eXtended Data Exchange) – which is based on OCAF. XDE offers a pre-defined document sub-structure to store colors, names, layers as well as other attributes (see XDE User’s Guide for details). This is done through a set of attributes defined in the XCAFDoc package that provides API to access data.

*Basic definitions*

Let’s start with assumption that your application uses OCAF for data description. In order to make your OCAF document XDE-compliant, you need to add XCAFDoc_DocumentTool attribute to your label of choice. It will add other required attributes to the sublabels. The easiest way is to extend your application class deriving TDocStd_Application, for example as follows:

DEFINE_STANDARD_HANDLE(OCC_UT_MyXDEApp,TDocStd_Application)
class OCC_UT_MyXDEApp : public TDocStd_Application
{
public:
//singleton pattern
Standard_EXPORT static const Handle(OCC_UT_MyXDEApp)& GetApplication();

virtual void Formats (TColStd_SequenceOfExtendedString& theFormats)
{ XCAFApp_Application::GetApplication()->Formats (theFormats); }

virtual Standard_CString ResourcesName()
{ return XCAFApp_Application::GetApplication()->ResourcesName(); }

Standard_EXPORT virtual void InitDocument (const Handle(TDocStd_Document)& theDoc) const;

protected:
OCC_UT_MyXDEApp() {}

public:
DEFINE_STANDARD_RTTI(OCC_UT_MyXDEApp)
};

IMPLEMENT_STANDARD_HANDLE(OCC_UT_MyXDEApp,TDocStd_Application)
IMPLEMENT_STANDARD_RTTIEXT(OCC_UT_MyXDEApp,TDocStd_Application)

const Handle(OCC_UT_MyXDEApp)& OCC_UT_MyXDEApp::GetApplication()
{
static Handle(OCC_UT_MyXDEApp) anApp = new OCC_UT_MyXDEApp;
return anApp;
}

void OCC_UT_MyXDEApp::InitDocument (const Handle(TDocStd_Document)& theDoc) const
{
//create a child of the main label and put XCAFDoc_DocumentTool there (i.e.
//one level below comparing to default XDE)
TDF_Label aL = theDoc->Main().FindChild (1, Standard_True); //0:1:1
XCAFDoc_DocumentTool::Set (aL.FindChild (1, Standard_True), Standard_False); //0:1:1:1
}

(to be continued)