New Post: can't get Line Markers to work....

I have a number of polylines and I'm trying to display direction arrows on them.
This is the code I'm using, but again, I think I'm missing something....

TLinePattern *ptrn = new TLinePattern(this);
TLineSegment *seg = new TLineSegment(this);
shape->DefaultDrawingOptions->LinePattern = ptrn->GetDefaultInterface();
seg->GetDefaultInterface() = shape->DefaultDrawingOptions->LinePattern->AddMarker(tkDefaultPointSymbol::dpsArrowDown);
seg->MarkerOutlineColor = clRed;
seg->MarkerSize = 10.0;
seg->MarkerInterval = 32;

What am I missing?
Any help appreciated.

BB