When you create a Bezier curve and enter the Edit mode, then you will see a greyed out menu item Spin in the Curve menu in the header.

How do i activate this menu item? How does it work?

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  • $\begingroup$ I don't know, but it seems a python-only tool, which maybe in the future will have a working ui entry. maybe. I found a reference to bpy.ops.curve.spin in docs.blender.org/api/blender_python_api_2_78a_release/… $\endgroup$ – m.ardito May 9 '17 at 10:02
  • $\begingroup$ Well, the same tool also exists for Surface. And here it is not greyed out. It spins the surface curve around the 3d cursor then. I am just curious why it is greyed out for a Bezier curve. $\endgroup$ – Tiles May 9 '17 at 10:33

The reason Spin is greyed out is because currently the UI file for that menu item is


Which points to an operator written in C


void CURVE_OT_spin(wmOperatorType *ot)

Inside that operator is a poll to check if the current state of blender warrants showing the menu entry as clickable.

ot->poll = ED_operator_editsurf;

this sets the value of ot->poll to whatever the value of ED_operator_editsurf is,


int ED_operator_editsurf(bContext *C)
    Object *obedit = CTX_data_edit_object(C);
    if (obedit && obedit->type == OB_SURF)
        return NULL != ((Curve *)obedit->data)->editnurb;
    return 0;

this tests if the object is in edit mode, it would be, and also tests the type of the object, which in that case is not OB_SURF, not a surface type curve.


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