Gui: add box geometry element selection command

Implement box element selection that support linked and grouped objects.
Also modified original box selection command to support the same with
the same code.

src/Mod/Part/App/TopoShape.cpp

@@ -3415,12 +3415,90 @@ void TopoShape::getPoints(std::vector<Base::Vector3d> &Points,
 }
 
 void TopoShape::getLinesFromSubelement(const Data::Segment* element,
-                                       std::vector<Base::Vector3d> &Points,
+                                       std::vector<Base::Vector3d> &vertices,
                                        std::vector<Line> &lines) const
 {
-    (void)element;
-    (void)Points;
-    (void)lines;
+    if (element->getTypeId() == ShapeSegment::getClassTypeId()) {
+        const TopoDS_Shape& shape = static_cast<const ShapeSegment*>(element)->Shape;
+        if (shape.IsNull())
+            return;
+        if(shape.ShapeType() == TopAbs_VERTEX) {
+            auto pnt = BRep_Tool::Pnt(TopoDS::Vertex(shape));
+            vertices.emplace_back(pnt.X(),pnt.Y(),pnt.Z());
+            return;
+        }
+
+        for(TopExp_Explorer exp(shape,TopAbs_EDGE);exp.More();exp.Next()) {
+
+            TopoDS_Edge aEdge = TopoDS::Edge(exp.Current());
+            TopLoc_Location aLoc;
+            Handle(Poly_Polygon3D) aPoly = BRep_Tool::Polygon3D(aEdge, aLoc);
+
+            gp_Trsf myTransf;
+            Standard_Integer nbNodesInFace;
+
+            auto line_start = vertices.size();
+
+            // triangulation succeeded?
+            if (!aPoly.IsNull()) {
+                if (!aLoc.IsIdentity()) {
+                    myTransf = aLoc.Transformation();
+                }
+                nbNodesInFace = aPoly->NbNodes();
+
+                const TColgp_Array1OfPnt& Nodes = aPoly->Nodes();
+
+                gp_Pnt V;
+                for (Standard_Integer i=0;i < nbNodesInFace;i++) {
+                    V = Nodes(i+1);
+                    V.Transform(myTransf);
+                    vertices.emplace_back(V.X(),V.Y(),V.Z());
+                }
+            }
+            else {
+                // the edge has not its own triangulation, but then a face the edge is attached to
+                // must provide this triangulation
+
+                // Look for one face in our map (it doesn't care which one we take)
+                auto aFace = findAncestorShape(aEdge, TopAbs_FACE);
+                if(aFace.IsNull())
+                    continue;
+
+                // take the face's triangulation instead
+                Handle(Poly_Triangulation) aPolyTria = BRep_Tool::Triangulation(TopoDS::Face(aFace),aLoc);
+                if (!aLoc.IsIdentity()) {
+                    myTransf = aLoc.Transformation();
+                }
+
+                if (aPolyTria.IsNull()) break;
+
+                // this holds the indices of the edge's triangulation to the actual points
+                Handle(Poly_PolygonOnTriangulation) aPoly = BRep_Tool::PolygonOnTriangulation(aEdge, aPolyTria, aLoc);
+                if (aPoly.IsNull())
+                    continue; // polygon does not exist
+
+                // getting size and create the array
+                nbNodesInFace = aPoly->NbNodes();
+
+                const TColStd_Array1OfInteger& indices = aPoly->Nodes();
+                const TColgp_Array1OfPnt& Nodes = aPolyTria->Nodes();
+
+                gp_Pnt V;
+                // go through the index array
+                for (Standard_Integer i=indices.Lower();i <= indices.Upper();i++) {
+                    V = Nodes(indices(i));
+                    V.Transform(myTransf);
+                    vertices.emplace_back(V.X(),V.Y(),V.Z());
+                }
+            }
+            
+            if(line_start+1 < vertices.size()) {
+                lines.emplace_back();
+                lines.back().I1 = line_start;
+                lines.back().I2 = vertices.size()-1;
+            }
+        }
+    }
 }
 
 void TopoShape::getFacesFromSubelement(const Data::Segment* element,