How to create Helix in c++?

Rhino Developer
1

Hi;
I want to create Helix by c++, it seem use the function RhinoGetHelix() ,but how do I use it ? Who can give me some examples ?

2

Hi @pythonuser,

How about this?

CRhinoCommand::result CCommandTest::RunCommand(const CRhinoCommandContext& context)
{
  CArgsRhinoGetSpiral args;
  ON_NurbsCurve helix;
  CRhinoCommand::result rc = RhinoGetHelix(args, helix);
  if (rc == CRhinoCommand::success)
  {
    context.m_doc.AddCurveObject(helix);
    context.m_doc.Redraw();
  }
  return rc;
}

Note, if you don’t care to use our UI, then just use RhinoCreateSpiral, which returns a NURBS curve. See rhinoSdkGetSpiral.h for more details.

– Dale

3

Hi@dale,
It is very helpful, thinks :smile:

4

Hi;
What is the problem in my code, the VS prompt : Error C2665: “RhinoCreateSpiral” : none of the three overloads can convert all parameter classes

CRhinoGetObject go;
go.SetCommandPrompt( L"select curve" );
go.SetGeometryFilter(CRhinoGetObject::curve_object);
go.EnableSubObjectSelect( FALSE );
go.EnableGroupSelect(FALSE);
go.GetObjects( 1, 1 );
if( go.CommandResult() != CRhinoCommand::success )
    return CRhinoCommand::cancel;

const ON_Curve* rail = go.Object(0).Curve();
ON_NurbsCurve helix;
CRhinoCommand::result rc = RhinoCreateSpiral(rail,rail->Domain().Min(),rail->Domain().Max(),rail->PointAtStart(),2.4,20,0.5,0.5,12,&helix);
if (rc == CRhinoCommand::success)
{
	context.m_doc.AddCurveObject(helix);
	context.m_doc.Redraw();
}
return rc;

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5

Hi @pythonuser,

Read the comments for each RhinoCreateSpiral function carefully, as each requires different input and creates a different type of curve.

Here is an example of creating a helix around a curve:

CRhinoCommand::result CCommandTest6::RunCommand(const CRhinoCommandContext& context)
{
  CRhinoGetObject go;
  go.SetCommandPrompt(L"Select curve");
  go.SetGeometryFilter(CRhinoGetObject::curve_object);
  go.SetGeometryAttributeFilter(CRhinoGetObject::open_curve);
  go.EnableSubObjectSelect(FALSE);
  go.GetObjects(1, 1);
  if (go.CommandResult() != CRhinoCommand::success)
    return CRhinoCommand::cancel;

  const CRhinoObjRef& objref = go.Object(0);
  const ON_Curve* curve = objref.Curve();
  if (nullptr == curve)
    return CRhinoCommand::failure;

  CArgsRhinoGetSpiral args;
  args.SetAroundCurve(TRUE);

  double t, t0, t1, tmid;
  objref.CurveParameter(&t);
  curve->GetDomain(&t0, &t1);
  curve->GetNormalizedArcLengthPoint(0.5, &tmid);

  args.SetRail(curve);

  // flip rail and t's if necessary
  if (t > tmid)
  {
    args.Rail()->Reverse();
    double d = t1; t1 = t0; t0 = d;
  }

  args.SetStartDir(curve->TangentAt(t0));
  args.SetStartPoint(curve->PointAt(t0));
  args.SetEndDir(curve->TangentAt(t1));
  args.SetEndPoint(curve->PointAt(t1));
  
  double d = ON_UNSET_VALUE;
  curve->GetLength(&d);
  args.SetLength(d);

  args.SetPitchMode(FALSE);

  if (args.PitchMode())
    args.SetTurns(args.Length() / 2.4);
  else
    args.SetPitch(args.Length() / 12);

  args.SetFirstRadius(0.5);
  args.SetSecondRadius(0.5);

  ON_NurbsCurve helix;

  bool rc = RhinoCreateSpiral(args, helix);
  if (rc)
  {
    context.m_doc.AddCurveObject(helix);
    context.m_doc.Redraw();
  }
  return rc ? CRhinoCommand::success : CRhinoCommand::failure;
}

– Dale

1 Like
6

Think you very much:grinning: