[Sketcher] Separate line-tangent-at-knot from angle-at-point

The latter is intended for a specific solver constraint.

[Sketcher] Make further changes for tangent-at-knot separation

1. Remove code for tangent-at-knot from `addAngleAtPointConstraint`.
2. Use correct order of input.
3. Separate internal C0 knot vs end knots. The latter can still be constrained
but the user must use endpoints of the spline instead of knots.

src/Mod/Sketcher/App/Sketch.cpp

@@ -1717,12 +1717,32 @@ int Sketch::addConstraint(const Constraint *constraint)
         break;
     case Tangent:
         if (constraint->FirstPos == PointPos::none &&
-                constraint->SecondPos == PointPos::none &&
-                constraint->Third == GeoEnum::GeoUndef){
+            constraint->SecondPos == PointPos::none &&
+            constraint->Third == GeoEnum::GeoUndef){
             //simple tangency
             rtn = addTangentConstraint(constraint->First,constraint->Second);
         }
         else {
+            // check for B-Spline Knot to curve tangency
+            if (constraint->FirstPos == PointPos::none &&
+                constraint->SecondPos == PointPos::none &&
+                constraint->ThirdPos == PointPos::start) {
+                auto knotgeoId = checkGeoId(constraint->Third);
+                if (Geoms[knotgeoId].type == Point) {
+                    auto *point = static_cast<const GeomPoint*>(Geoms[knotgeoId].geo);
+
+                    if (GeometryFacade::isInternalType(point,InternalType::BSplineKnotPoint)) {
+                        auto bsplinegeoid = internalAlignmentGeometryMap.at(constraint->Third);
+
+                        bsplinegeoid = checkGeoId(bsplinegeoid);
+
+                        auto linegeoid = checkGeoId(constraint->Second);
+
+                        return addTangentLineAtBSplineKnotConstraint(linegeoid, bsplinegeoid, knotgeoId);
+                    }
+                }
+            }
+
             //any other point-wise tangency (endpoint-to-curve, endpoint-to-endpoint, tangent-via-point)
             c.value = new double(constraint->getValue());
             if(c.driving)
@@ -1733,10 +1753,10 @@ int Sketch::addConstraint(const Constraint *constraint)
             }
 
             rtn = addAngleAtPointConstraint(
-                        constraint->First, constraint->FirstPos,
-                        constraint->Second, constraint->SecondPos,
-                        constraint->Third, constraint->ThirdPos,
-                        c.value, constraint->Type, c.driving);
+                constraint->First, constraint->FirstPos,
+                constraint->Second, constraint->SecondPos,
+                constraint->Third, constraint->ThirdPos,
+                c.value, constraint->Type, c.driving);
         }
         break;
     case Distance:
@@ -2434,6 +2454,48 @@ int Sketch::addTangentConstraint(int geoId1, int geoId2)
     return -1;
 }
 
+int Sketch::addTangentLineAtBSplineKnotConstraint(int checkedlinegeoId, int checkedbsplinegeoId, int checkedknotgeoid)
+{
+    GCS::BSpline &b = BSplines[Geoms[checkedbsplinegeoId].index];
+    GCS::Line &l = Lines[Geoms[checkedlinegeoId].index];
+
+    size_t knotindex = b.knots.size();
+
+    auto knotIt = std::find(b.knotpointGeoids.begin(),
+                    b.knotpointGeoids.end(), checkedknotgeoid);
+
+    knotindex = std::distance(b.knotpointGeoids.begin(), knotIt);
+
+    if (knotindex >= b.knots.size()){
+        Base::Console().Error("addConstraint: Knot index out-of-range!\n");
+        return -1;
+    }
+
+    if (b.mult[knotindex] >= b.degree) {
+        if (b.periodic || (knotindex > 0 && knotindex < (b.knots.size()-1))) {
+            Base::Console().Error("addTangentLineAtBSplineKnotConstraint: cannot set constraint when B-spline slope is discontinuous at knot!\n");
+            return -1;
+        }
+        else {
+            // TODO: Let angle-at-point do the work. Requires a `double * value`
+            // return addAngleAtPointConstraint(
+            //     linegeoid, PointPos::none,
+            //     bsplinegeoid, PointPos::none,
+            //     knotgeoId, PointPos::start,
+            //     nullptr, Tangent, true);
+
+            // For now we just throw an error.
+            Base::Console().Error("addTangentLineAtBSplineKnotConstraint: This method cannot set tangent constraint at end knots of a B-spline. Please constrain the start/end points instead.\n");
+            return -1;
+        }
+    }
+    else {
+        int tag = Sketch::addPointOnObjectConstraint(checkedknotgeoid, PointPos::start, checkedlinegeoId);//increases ConstraintsCounter
+        GCSsys.addConstraintTangentAtBSplineKnot(b, l, knotindex, tag);
+        return ConstraintsCounter;
+    }
+}
+
 //This function handles any type of tangent, perpendicular and angle
 // constraint that involves a point.
 // i.e. endpoint-to-curve, endpoint-to-endpoint and tangent-via-point
@@ -2467,48 +2529,6 @@ int Sketch::addAngleAtPointConstraint(
     if(avp)
         geoId3 = checkGeoId(geoId3);
 
-    if ((Geoms[geoId1].type == BSpline && Geoms[geoId2].type == Line) ||
-        (Geoms[geoId1].type == Line && Geoms[geoId2].type == BSpline)) {
-        if (cTyp == Tangent) {
-            if (Geoms[geoId1].type == Line && Geoms[geoId2].type == BSpline) {
-                std::swap(geoId1, geoId2);
-                std::swap(pos1, pos2);
-            }
-            GCS::BSpline &b = BSplines[Geoms[geoId1].index];
-            GCS::Line &l = Lines[Geoms[geoId2].index];
-            size_t knotindex = b.knots.size();
-            if (avp) {
-                auto knotIt = std::find(b.knotpointGeoids.begin(),
-                                        b.knotpointGeoids.end(), geoId3);
-                knotindex =
-                    std::distance(b.knotpointGeoids.begin(), knotIt);
-            }
-            else {
-                knotindex = (pos1 == PointPos::start) ? 0 : (b.knots.size() - 1);
-            }
-            if (knotindex >= b.knots.size())
-                return -1;
-
-            if (b.mult[knotindex] >= b.degree) {
-                // Leave handling of start/end of non-periodic B-splines to legacy code
-                if (b.periodic ||
-                    (pos1 != PointPos::start && pos1 != PointPos::end)) {
-                    Base::Console().Error("addAngleAtPointConstraint: cannot set constraint when B-spline slope is discontinuous at knot!\n");
-                    return -1;
-                }
-            }
-            else {
-                int tag;
-                if(e2c)
-                    tag = Sketch::addPointOnObjectConstraint(geoId1, pos1, geoId2, driving);//increases ConstraintsCounter
-                else
-                    tag = ++ConstraintsCounter;
-                GCSsys.addConstraintTangentAtBSplineKnot(b, l, knotindex, tag, driving);
-                return ConstraintsCounter;
-            }
-        }
-    }
-
     if (Geoms[geoId1].type == Point ||
         Geoms[geoId2].type == Point){
         Base::Console().Error("addAngleAtPointConstraint: one of the curves is a point!\n");

src/Mod/Sketcher/App/Sketch.h

@@ -282,6 +282,7 @@ public:
     int addPerpendicularConstraint(int geoId1, int geoId2);
     /// add a tangency constraint between two geometries
     int addTangentConstraint(int geoId1, int geoId2);
+    int addTangentLineAtBSplineKnotConstraint(int checkedlinegeoId, int checkedbsplinegeoId, int checkedknotgeoid);
     int addAngleAtPointConstraint(
             int geoId1, PointPos pos1,
             int geoId2, PointPos pos2,