Sketcher: Driving/reference creation improvements and some other fixes

======================================================================

- Changing from Driving to reference does not include unnecessary solvings.
- Added some checks to avoid making Driving constraints when calling directly from python and involving only external geometry (would give redundant constraints).
- New python command toggleDriving to just change the status from reference to Driving
- New UI toolbar Command to toggle constraints
- Fix to allow switching from/to construction mode during continuous mode creation.
- Enable/Disable for constraints in constraints widget has changed to operate on multiselection and now effects "toggle" instead of enable/disable.
- Disable the option to directly create a SnellsLaw non-driving constraint (this constraint does not support direct creation, it can be toggled to non-driving after creation though).

src/Mod/Sketcher/App/SketchObject.cpp

@@ -234,7 +234,10 @@ int SketchObject::setDriving(int ConstrId, bool isdriving)
         type != Radius &&
         type != Angle &&
         type != SnellsLaw)
-        return -1;
+        return -2;
+    
+    if (!(vals[ConstrId]->First>=0 || vals[ConstrId]->Second>=0 || vals[ConstrId]->Third>=0) && isdriving==true)
+        return -3; // a constraint that does not have at least one element as not-external-geometry can never be driving.
 
     // copy the list
     std::vector<Constraint *> newVals(vals);
@@ -245,11 +248,7 @@ int SketchObject::setDriving(int ConstrId, bool isdriving)
     this->Constraints.setValues(newVals);
     delete constNew;
 
-    int err = solve();
-    if (err)
-        this->Constraints.setValues(vals);
-
-    return err;
+    return 0;
 }
 
 int SketchObject::getDriving(int ConstrId, bool &isdriving)
@@ -273,6 +272,38 @@ int SketchObject::getDriving(int ConstrId, bool &isdriving)
     return 0;
 }
 
+int SketchObject::toggleDriving(int ConstrId)
+{
+    const std::vector<Constraint *> &vals = this->Constraints.getValues();
+    
+    if (ConstrId < 0 || ConstrId >= int(vals.size()))
+        return -1;
+    
+    ConstraintType type = vals[ConstrId]->Type;
+    
+    if (type != Distance &&
+        type != DistanceX &&
+        type != DistanceY &&
+        type != Radius &&
+        type != Angle &&
+        type != SnellsLaw)
+        return -2;
+    
+    if (!(vals[ConstrId]->First>=0 || vals[ConstrId]->Second>=0 || vals[ConstrId]->Third>=0) && vals[ConstrId]->isDriving==false)
+        return -3; // a constraint that does not have at least one element as not-external-geometry can never be driving.
+        
+    // copy the list
+    std::vector<Constraint *> newVals(vals);
+    // clone the changed Constraint
+    Constraint *constNew = vals[ConstrId]->clone();
+    constNew->isDriving = !constNew->isDriving;
+    newVals[ConstrId] = constNew;
+    this->Constraints.setValues(newVals);
+    delete constNew;
+
+    return 0;
+}
+
 int SketchObject::movePoint(int GeoId, PointPos PosId, const Base::Vector3d& toPoint, bool relative)
 {
     Sketch sketch;
@@ -489,7 +520,7 @@ int SketchObject::setConstruction(int GeoId, bool on)
     newVals[GeoId]=geoNew;
 
     this->Geometry.setValues(newVals);
-    this->Constraints.acceptGeometry(getCompleteGeometry());
+    //this->Constraints.acceptGeometry(getCompleteGeometry()); <= This is not necessary for a toggle. Reducing redundant solving. Abdullah
     return 0;
 }
 

src/Mod/Sketcher/App/SketchObject.h

@@ -114,6 +114,8 @@ public:
     int setDriving(int ConstrId, bool isdriving);
     /// get the driving status of this constraint
     int getDriving(int ConstrId, bool &isdriving);
+    /// toggle the driving status of this constraint
+    int toggleDriving(int ConstrId);
     /// move this point to a new location and solve
     int movePoint(int GeoId, PointPos PosId, const Base::Vector3d& toPoint, bool relative=false);
     /// retrieves the coordinates of a point

src/Mod/Sketcher/App/SketchObjectPy.xml

@@ -87,6 +87,11 @@
       <Documentation>
         <UserDocu>Get the Driving status of a datum constraint</UserDocu>
       </Documentation>
+    </Methode>
+    <Methode Name="toggleDriving">
+      <Documentation>
+        <UserDocu>toggle the Driving status of a datum constraint</UserDocu>
+      </Documentation>
     </Methode>    
     <Methode Name="movePoint">
       <Documentation>

src/Mod/Sketcher/App/SketchObjectPyImp.cpp

@@ -49,7 +49,7 @@ using namespace Sketcher;
 
 // returns a string which represents the object e.g. when printed in python
 std::string SketchObjectPy::representation(void) const
-{
+{        
     return "<Sketcher::SketchObject>";
 }
 
@@ -578,7 +578,7 @@ PyObject* SketchObjectPy::setDriving(PyObject *args)
 
     if (this->getSketchObjectPtr()->setDriving(constrid, PyObject_IsTrue(driving) ? true : false)) {
         std::stringstream str;
-        str << "Not able set Driving for constraint with the given index: " << constrid;
+        str << "Not able set Driving/reference for constraint with the given index: " << constrid;
         PyErr_SetString(PyExc_ValueError, str.str().c_str());
         return 0;
     }
@@ -603,6 +603,23 @@ PyObject* SketchObjectPy::getDriving(PyObject *args)
     return Py::new_reference_to(Py::Boolean(driving));
 }
 
+PyObject* SketchObjectPy::toggleDriving(PyObject *args)
+{
+    int constrid;
+    
+    if (!PyArg_ParseTuple(args, "i", &constrid))
+        return 0;
+
+    if (this->getSketchObjectPtr()->toggleDriving(constrid)) {
+        std::stringstream str;
+        str << "Not able toggle Driving for constraint with the given index: " << constrid;
+        PyErr_SetString(PyExc_ValueError, str.str().c_str());
+        return 0;
+    }
+
+    Py_Return;
+}
+
 
 PyObject* SketchObjectPy::movePoint(PyObject *args)
 {