0027875: GeomFill_NSections constructor crash on sequence of curve containing only one curve

The GeomFill_NSections algorithm cannot create any surface from sequence with single curve only.

Therefore, return is provided in corresponding place of the code. Additionally, some public methods of GeomFill_NSections class checks if the surface has been created earlier.

Test case for this issue has been created.

Compiler error has been eliminated.

src/GeomFill/GeomFill_NSections.cxx

@@ -524,6 +524,12 @@ GeomFill_NSections::GeomFill_NSections(const TColGeom_SequenceOfCurve& NC,
     Standard_Real myPres3d = 1.e-06;
     Standard_Integer i,j,jdeb=1,jfin=mySections.Length();
     
+    if (jfin <= jdeb)
+    {
+      //We will not be able to create surface from single curve.
+      return;
+    }
+
     GeomFill_SectionGenerator section;
     Handle(Geom_BSplineSurface) surface;
 
@@ -641,9 +647,12 @@ GeomFill_NSections::GeomFill_NSections(const TColGeom_SequenceOfCurve& NC,
                                             Standard_Integer& NbKnots,
                                             Standard_Integer& Degree) const
 {
-   NbPoles = mySurface->NbUPoles();
-   NbKnots = mySurface->NbUKnots();
-   Degree  = mySurface->UDegree();
+  if (mySurface.IsNull())
+    return;
+  
+  NbPoles = mySurface->NbUPoles();
+  NbKnots = mySurface->NbUKnots();
+  Degree  = mySurface->UDegree();
 }
 
 //=======================================================
@@ -651,7 +660,8 @@ GeomFill_NSections::GeomFill_NSections(const TColGeom_SequenceOfCurve& NC,
 //=======================================================
  void GeomFill_NSections::Knots(TColStd_Array1OfReal& TKnots) const
 {
-  mySurface->UKnots(TKnots);
+  if (!mySurface.IsNull())
+    mySurface->UKnots(TKnots);
 }
 
 //=======================================================
@@ -659,7 +669,8 @@ GeomFill_NSections::GeomFill_NSections(const TColGeom_SequenceOfCurve& NC,
 //=======================================================
  void GeomFill_NSections::Mults(TColStd_Array1OfInteger& TMults) const
 {
-  mySurface->UMultiplicities(TMults);
+  if (!mySurface.IsNull())
+    mySurface->UMultiplicities(TMults);
 }
 
 
@@ -668,7 +679,10 @@ GeomFill_NSections::GeomFill_NSections(const TColGeom_SequenceOfCurve& NC,
 //=======================================================
  Standard_Boolean GeomFill_NSections::IsRational() const
 {
-  return mySurface->IsURational();
+  if (!mySurface.IsNull())
+    return mySurface->IsURational();
+
+  return Standard_False;
 }
 
 //=======================================================
@@ -676,7 +690,10 @@ GeomFill_NSections::GeomFill_NSections(const TColGeom_SequenceOfCurve& NC,
 //=======================================================
  Standard_Boolean GeomFill_NSections::IsUPeriodic() const
 {
-  return  mySurface->IsUPeriodic();
+  if (!mySurface.IsNull())
+    return  mySurface->IsUPeriodic();
+
+  return Standard_False;
 }
 
 //=======================================================
@@ -684,7 +701,10 @@ GeomFill_NSections::GeomFill_NSections(const TColGeom_SequenceOfCurve& NC,
 //=======================================================
  Standard_Boolean GeomFill_NSections::IsVPeriodic() const
 {
-  return  mySurface->IsVPeriodic();
+  if (!mySurface.IsNull())
+    return  mySurface->IsVPeriodic();
+
+  return Standard_False;
 }
 
 //=======================================================
@@ -692,6 +712,9 @@ GeomFill_NSections::GeomFill_NSections(const TColGeom_SequenceOfCurve& NC,
 //=======================================================
  Standard_Integer GeomFill_NSections::NbIntervals(const GeomAbs_Shape S) const
 {
+  if (mySurface.IsNull())
+    return 0;
+
   GeomAdaptor_Surface AdS(mySurface);
   return AdS.NbVIntervals(S);
 }
@@ -703,6 +726,9 @@ GeomFill_NSections::GeomFill_NSections(const TColGeom_SequenceOfCurve& NC,
  void GeomFill_NSections::Intervals(TColStd_Array1OfReal& T,
                                          const GeomAbs_Shape S) const
 {
+  if (mySurface.IsNull())
+    return;
+
   GeomAdaptor_Surface AdS(mySurface);
   AdS.VIntervals(T,S);
 }
@@ -763,6 +789,9 @@ GeomFill_NSections::GeomFill_NSections(const TColGeom_SequenceOfCurve& NC,
   gp_Pnt P, Bary;
   Bary.SetCoord(0., 0., 0.);
 
+  if (mySurface.IsNull())
+    return Bary;
+
   Standard_Integer ii,jj;
   Standard_Real U0, U1, V0, V1;
   mySurface->Bounds(U0,U1,V0,V1);
@@ -801,6 +830,9 @@ GeomFill_NSections::GeomFill_NSections(const TColGeom_SequenceOfCurve& NC,
 //=======================================================
 void GeomFill_NSections::GetMinimalWeight(TColStd_Array1OfReal& Weights) const
 {
+  if (mySurface.IsNull())
+    return;
+
   if (mySurface->IsURational()) {
     Standard_Integer NbU = mySurface->NbUPoles(),
                      NbV = mySurface->NbVPoles();

src/QABugs/QABugs_20.cxx

@@ -2114,6 +2114,33 @@ static Standard_Integer OCC27552(Draw_Interpretor&,
   return 0;
 }
 
+#include <NCollection_IncAllocator.hxx>
+static Standard_Integer OCC27875(Draw_Interpretor& theDI,
+                                 Standard_Integer theNArg,
+                                 const char ** theArgVal)
+{
+  if (theNArg < 2)
+  {
+    theDI << "Use: OCC27875 curve\n";
+  }
+
+  TColGeom_SequenceOfCurve aNC(new NCollection_IncAllocator());
+
+  const Handle(Geom_Curve) aC = Handle(Geom_Curve)::DownCast(DrawTrSurf::Get(theArgVal[1]));
+
+  aNC.Append(aC);
+
+  GeomFill_NSections aNS(aNC);
+
+  if (aNS.BSplineSurface().IsNull())
+  {
+    theDI << "GeomFill_NSections is not done.\n";
+  }
+
+  return 0;
+}
+
+
 void QABugs::Commands_20(Draw_Interpretor& theCommands) {
   const char *group = "QABugs";
 
@@ -2132,5 +2159,7 @@ void QABugs::Commands_20(Draw_Interpretor& theCommands) {
   theCommands.Add ("OCC27357", "OCC27357", __FILE__, OCC27357, group);
   theCommands.Add("OCC26270", "OCC26270 shape result", __FILE__, OCC26270, group);
   theCommands.Add ("OCC27552", "OCC27552", __FILE__, OCC27552, group); 
+  theCommands.Add("OCC27875", "OCC27875 curve", __FILE__, OCC27875, group);
+
   return;
 }

tests/bugs/modalg_6/bug27875

@@ -0,0 +1,19 @@
+puts "================"
+puts "OCC27875"
+puts "================"
+puts ""
+###############################
+## GeomFill_NSections constructor crash on sequence of curve containing only one curve
+###############################
+
+# GeomFill_NSections does not work if the sequence of curves contains only single curve.
+# Therefore, we should not expect any correct result from this operation. However, the
+# exception must not be thrown.
+
+pload QAcommands
+
+restore [locate_data_file OCC606_2.brep] w2
+explode w2 e
+mkcurve cc w2_1
+trim cc cc
+OCC27875 cc