Sketcher: implement command to decrease degree of a B-spline

src/Mod/Sketcher/App/SketchObject.cpp

@@ -5198,6 +5198,48 @@ bool SketchObject::increaseBSplineDegree(int GeoId, int degreeincrement /*= 1*/)
     return true;
 }
 
+bool SketchObject::decreaseBSplineDegree(int GeoId, int degreedecrement /*= 1*/)
+{
+    Base::StateLocker lock(managedoperation, true); // no need to check input data validity as this is an sketchobject managed operation.
+
+    if (GeoId < 0 || GeoId > getHighestCurveIndex())
+        return false;
+
+    const Part::Geometry *geo = getGeometry(GeoId);
+
+    if (geo->getTypeId() != Part::GeomBSplineCurve::getClassTypeId())
+        return false;
+
+    const Part::GeomBSplineCurve *bsp = static_cast<const Part::GeomBSplineCurve *>(geo);
+
+    const Handle(Geom_BSplineCurve) curve = Handle(Geom_BSplineCurve)::DownCast(bsp->handle());
+
+    std::unique_ptr<Part::GeomBSplineCurve> bspline(new Part::GeomBSplineCurve(curve));
+
+    try {
+        int cdegree = bspline->getDegree();
+
+        bool ok = bspline->approximate(Precision::Confusion(), 20, cdegree-degreedecrement, 0);
+        if (!ok)
+            return false;
+    }
+    catch (const Base::Exception& e) {
+        Base::Console().Error("%s\n", e.what());
+        return false;
+    }
+
+    const std::vector< Part::Geometry * > &vals = getInternalGeometry();
+
+    std::vector< Part::Geometry * > newVals(vals);
+
+    newVals[GeoId] = bspline.release();
+
+    // AcceptGeometry called from onChanged
+    Geometry.setValues(newVals);
+
+    return true;
+}
+
 bool SketchObject::modifyBSplineKnotMultiplicity(int GeoId, int knotIndex, int multiplicityincr)
 {
     Base::StateLocker lock(managedoperation, true); // no need to check input data validity as this is an sketchobject managed operation.

src/Mod/Sketcher/App/SketchObject.h

@@ -253,6 +253,14 @@ public:
      */
     bool increaseBSplineDegree(int GeoId, int degreeincrement = 1);
 
+    /*!
+     \brief Decreases the degree of a BSpline by degreedecrement, which defaults to 1
+     \param GeoId - the geometry of type bspline to increase the degree
+     \param degreedecrement - the decrement in number of degrees to effect
+     \retval bool - returns true if the decrease in degree succeeded, or false if it did not succeed.
+     */
+    bool decreaseBSplineDegree(int GeoId, int degreedecrement = 1);
+
     /*!
      \brief Increases or Decreases the multiplicity of a BSpline knot by the multiplicityincr param, which defaults to 1, if the result is multiplicity zero, the knot is removed
      \param GeoId - the geometry of type bspline to increase the degree

src/Mod/Sketcher/App/SketchObjectPy.xml

@@ -257,6 +257,11 @@ If there is no such constraint an exception is raised.
             <UserDocu>Increases the given BSpline Degree by a number of degrees</UserDocu>
         </Documentation>
     </Methode>
+    <Methode Name="decreaseBSplineDegree">
+        <Documentation>
+            <UserDocu>Decreases the given BSpline Degree by a number of degrees by approximating this curve</UserDocu>
+        </Documentation>
+    </Methode>
     <Methode Name="modifyBSplineKnotMultiplicity">
         <Documentation>
             <UserDocu>Increases or reduces the given BSpline knot multiplicity</UserDocu>

src/Mod/Sketcher/App/SketchObjectPyImp.cpp

@@ -1396,6 +1396,24 @@ PyObject* SketchObjectPy::increaseBSplineDegree(PyObject *args)
     Py_Return;
 }
 
+PyObject* SketchObjectPy::decreaseBSplineDegree(PyObject *args)
+{
+    int GeoId;
+    int incr = 1;
+
+    if (!PyArg_ParseTuple(args, "i|i", &GeoId, &incr))
+        return 0;
+
+    if (this->getSketchObjectPtr()->decreaseBSplineDegree(GeoId, incr)==false) {
+        std::stringstream str;
+        str << "Degree decrease failed for: " << GeoId;
+        PyErr_SetString(PyExc_ValueError, str.str().c_str());
+        return 0;
+    }
+
+    Py_Return;
+}
+
 PyObject* SketchObjectPy::modifyBSplineKnotMultiplicity(PyObject *args)
 {
     int GeoId;

src/Mod/Sketcher/Gui/CommandSketcherBSpline.cpp

@@ -479,8 +479,7 @@ CmdSketcherDecreaseDegree::CmdSketcherDecreaseDegree()
     sAppModule      = "Sketcher";
     sGroup          = QT_TR_NOOP("Sketcher");
     sMenuText       = QT_TR_NOOP("Decrease B-spline degree");
-    sToolTipText    = QT_TR_NOOP("Decreases the degree of the B-spline.\n"
-                                 "This command is currently NOT IMPLEMENTED.");
+    sToolTipText    = QT_TR_NOOP("Decreases the degree of the B-spline");
     sWhatsThis      = "Sketcher_BSplineDecreaseDegree";
     sStatusTip      = sToolTipText;
     sPixmap         = "Sketcher_BSplineDecreaseDegree";
@@ -488,12 +487,54 @@ CmdSketcherDecreaseDegree::CmdSketcherDecreaseDegree()
     eType           = ForEdit;
 }
 
-// TODO: fully implement this function to complement Sketcher_BSplineIncreaseDegree
 void CmdSketcherDecreaseDegree::activated(int iMsg)
 {
     Q_UNUSED(iMsg);
-    Base::Console().Message("Decrease degree of spline. "
-                            "This command is currently NOT IMPLEMENTED.\n");
+
+    // get the selection
+    std::vector<Gui::SelectionObject> selection;
+    selection = getSelection().getSelectionEx(0, Sketcher::SketchObject::getClassTypeId());
+
+    // only one sketch with its subelements are allowed to be selected
+    if (selection.size() != 1) {
+        return;
+    }
+
+    // get the needed lists and objects
+    const std::vector<std::string> &SubNames = selection[0].getSubNames();
+    Sketcher::SketchObject* Obj = static_cast<Sketcher::SketchObject*>(selection[0].getObject());
+
+    openCommand("Decrease spline degree");
+
+    bool ignored = false;
+
+    for (size_t i=0; i < SubNames.size(); i++) {
+        // only handle edges
+        if (SubNames[i].size() > 4 && SubNames[i].substr(0,4) == "Edge") {
+            int GeoId = std::atoi(SubNames[i].substr(4,4000).c_str()) - 1;
+            const Part::Geometry * geo = Obj->getGeometry(GeoId);
+
+            if (geo->getTypeId() == Part::GeomBSplineCurve::getClassTypeId()) {
+                Gui::cmdAppObjectArgs(selection[0].getObject(), "decreaseBSplineDegree(%d) ", GeoId);
+                // add new control points
+                //Gui::cmdAppObjectArgs(selection[0].getObject(), "exposeInternalGeometry(%d)", GeoId);
+            }
+            else {
+                ignored = true;
+            }
+        }
+    }
+
+    if (ignored) {
+        QMessageBox::warning(Gui::getMainWindow(),
+                             QObject::tr("Wrong selection"),
+                             QObject::tr("At least one of the selected "
+                                         "objects was not a B-Spline and was ignored."));
+    }
+
+    commitCommand();
+    tryAutoRecomputeIfNotSolve(Obj);
+    getSelection().clearSelection();
 }
 
 bool CmdSketcherDecreaseDegree::isActive(void)
@@ -902,7 +943,7 @@ void CreateSketcherCommandsBSpline(void)
     rcCmdMgr.addCommand(new CmdSketcherCompBSplineShowHideGeometryInformation());
     rcCmdMgr.addCommand(new CmdSketcherConvertToNURB());
     rcCmdMgr.addCommand(new CmdSketcherIncreaseDegree());
-    rcCmdMgr.addCommand(new CmdSketcherDecreaseDegree());  // TODO: implement this function
+    rcCmdMgr.addCommand(new CmdSketcherDecreaseDegree());
     rcCmdMgr.addCommand(new CmdSketcherIncreaseKnotMultiplicity());
     rcCmdMgr.addCommand(new CmdSketcherDecreaseKnotMultiplicity());
     rcCmdMgr.addCommand(new CmdSketcherCompModifyKnotMultiplicity());

src/Mod/Sketcher/Gui/Workbench.cpp

@@ -373,7 +373,7 @@ inline void SketcherAddWorkbenchBSplines<Gui::MenuItem>(Gui::MenuItem& bspline)
         << "Sketcher_BSplineKnotMultiplicity"
         << "Sketcher_BSplineConvertToNURB"
         << "Sketcher_BSplineIncreaseDegree"
-        << "Sketcher_BSplineDecreaseDegree"  // TODO: implement this command
+        << "Sketcher_BSplineDecreaseDegree"
         << "Sketcher_BSplineIncreaseKnotMultiplicity"
         << "Sketcher_BSplineDecreaseKnotMultiplicity";
 }
@@ -384,7 +384,7 @@ inline void SketcherAddWorkbenchBSplines<Gui::ToolBarItem>(Gui::ToolBarItem& bsp
     bspline << "Sketcher_CompBSplineShowHideGeometryInformation"
     << "Sketcher_BSplineConvertToNURB"
     << "Sketcher_BSplineIncreaseDegree"
-    << "Sketcher_BSplineDecreaseDegree"  // TODO: implement this command
+    << "Sketcher_BSplineDecreaseDegree"
     << "Sketcher_CompModifyKnotMultiplicity";
 }