Work with assemblies

Hi Adriana,

You may want to checkout branch CR29032 of OpenCascade from GitWeb (you may download the snapshot). The corresponding ticket is https://tracker.dev.opencascade.org/view.php?id=29032. In this branch, you can find new tool: XCAFDoc_AssemblyGraph. This tool is designed to ease your life and give you an explicit representation of assembly structure.

You initialize it like this:

Handle(TDocStd_Document) doc = ...; // Your XDE document

// Prepare assembly graph
Handle(XCAFDoc_AssemblyGraph) asmGraph = new XCAFDoc_AssemblyGraph(doc, true);

It gives you the assembly graph explicitly. You can then iterate nodes and arcs ("part-of" relations) like this:

// Iterate nodes
const NCollection_IndexedMap<XCAFDoc_ObjectId>& nodes = asmGraph->GetNodes();
//
for ( int n = 1; n <= nodes.Extent(); ++n )
{
  // Get type of a graph node
  const int nodeType = asmGraph->GetNodeType(n);

  ...

}

// Iterate arcs (adjacency matrix)
const XCAFDoc_AssemblyGraph::t_adjacency& arcs = asmGraph->GetArcs();
//
for ( XCAFDoc_AssemblyGraph::t_adjacency::Iterator it(arcs); it.More(); it.Next() )
{
  const int                         parentId = it.Key();
  const TColStd_PackedMapOfInteger& children = it.Value();

  // Loop over the children
  for ( TColStd_MapIteratorOfPackedMapOfInteger cit(children); cit.More(); cit.Next() )
  {
    const int childId = cit.Key();

    std::cout << "(parent, child) = "
              << "("
              << parentId
              << ", "
              << childId
              << ")"
              << std::endl;
  }
}

If you want to build a scene graph from your assembly (like in the picture attached), you may iterate the graph recursively together with populating your GUI view:

void IterateGraph(const Handle(XCAFDoc_AssemblyGraph)& asmGraph)
{
  // Loop over the roots
  const TColStd_PackedMapOfInteger& roots = asmGraph->GetRoots();
  //
  for ( TColStd_MapIteratorOfPackedMapOfInteger rit(roots); rit.More(); rit.Next() )
  {
    const int rootId = rit.Key();

    // Populate UI here

    // Loop over the children recursively
    IterateChildren(rootId, asmGraph);
  }
}

void IterateChildren(const int                            rootId,
                     const Handle(XCAFDoc_AssemblyGraph)& asmGraph)
{
  if ( !asmGraph->HasChildren(rootId) )
    return;

  // Iterate children
  const TColStd_PackedMapOfInteger& children = asmGraph->GetChildren(rootId);
  //
  for ( TColStd_MapIteratorOfPackedMapOfInteger cit(children); cit.More(); cit.Next() )
  {
    const int childId = cit.Key();

    // Populate UI here

    // Repeat recursively
    IterateChildren(childId, asmGraph);
  }
}

GetPersistentId() method of XCAFDoc_AssemblyGraph returns string ID for the OCAF label corresponding to the given assembly element. This entry can be used to access the data with XCAFDoc_ShapeTool (unless we do not have more higher-level interfaces to XDE). This way geometry is separated from assembly (conceptual) structure.

I shall be glad to hear about your experience with this interface for assemblies. The branch is under development, so any remarks are welcome.