Moving Curve and Surface Grips
Windows only

by Dale Fugier (Last updated:  Wednesday, December 5, 2018)

Problem

You would like to move the control points of a curve or surface object using the Rhino C/C++ SDK.

Solution

The curve and surface grips you see on the screen, after running Rhino’s PointsOn command, are represented by CRhinoGripObject-derived objects. To move a grip object, you have to do a few things:

  1. Get a CRhinoGripObject. You can use a CRhinoGetObject object to do this.
  2. Call CRhinoGripObject::MoveGrip to transform the grip’s location.
  3. Call CRhinoGripObject::Owner to get the grips owning CRhinoObject object.
  4. Call CRhinoObject::NewObject to create a new CRhinoObject object based on the new grip location.
  5. Call CRhinoDoc::ReplaceObject to replace the original owning object with the new one.

Sample

The following sample code demonstrates this.

NOTE: This sample uses a CRhinoXformObjectList object to maintain the list of grips and grip owners.

CRhinoCommand::result CCommandMoveGrips::RunCommand( const CRhinoCommandContext& context )
{
  CRhinoGetObject go;
  go.SetCommandPrompt( L"Select grips to move" );
  go.SetGeometryFilter( CRhinoGetObject::grip_object );
  go.GetObjects( 1, 0 );
  if( go.CommandResult() != success )
    return go.CommandResult();
 
  CRhinoXformObjectList xform_list;
  if( xform_list.AddObjects(go, true) < 1 )
    return failure;
 
  CRhinoGetPoint gp;
  gp.SetCommandPrompt( L"Point to move from" );
  gp.GetPoint();
  if( gp.CommandResult() != success )
    return gp.CommandResult();
 
  ON_3dPoint from = gp.Point();
 
  gp.SetCommandPrompt( L"Point to move to" );
  gp.SetBasePoint( from );
  gp.DrawLineFromPoint( from, TRUE );
  gp.GetPoint();
  if( gp.CommandResult() != success )
    return gp.CommandResult();
 
  ON_3dPoint to = gp.Point();
 
  ON_Xform xform;
  xform.Translation( to - from );
  if( xform.IsValid() )
  {
    // Transform the grip objects
    int i;
    for( i = 0; i < xform_list.m_grips.Count(); i++ )
      xform_list.m_grips[i]->MoveGrip( xform );
 
    // Replace the old owner with a new one
    for( i = 0; i < xform_list.m_grip_owners.Count(); i++ )
    {
      CRhinoObject* old_object = xform_list.m_grip_owners[i];
      if( old_object )
      {
        CRhinoObject* new_object = old_object->m_grips->NewObject();
        if( new_object )
          context.m_doc.ReplaceObject( CRhinoObjRef(old_object), new_object, true );
      }
    }
 
    context.m_doc.Redraw();
  }
 
  return success;
}