How to get a tree structure of any supported drawing file?

To get a tree structure of any drawing file (IGES, DWG, DXF, etc.) for visualization with a tree component (for example, TTreeView), you need to iterate through entities in the given file and add each entity to the structure using the following recursive procedure.

uses
  ..., ComCtrls;

type
  tvStructure: TTreeView;

...

implementation

...

procedure Add(AParent: TTreeNode; AEnt: TsgDXFEntity);
var
  I: Integer;
begin
  if Assigned(AEnt) then
  begin
    AParent := tvStructure.Items.AddChildObject(Parent, AEnt.EntName, AEnt);
    Application.ProcessMessages;
    for I := 0 to AEnt.Count - 1 do Add(AParent, AEnt[I]);
  end;
end;

Note

The Entities[const AIndex: Integer]: TsgDXFEntity read GetEntity; default property has the default directive. That's why you can use the property in a more convenient way like AEnt[I] instead of AEnt.Entities[I].