Sketcher: Add backwards-compat path for external geo

Before 0aed23c (PR #19582), external geometry projection used a different algorithm and produced slightly different geometry for some kinds of projections (B-splines in particular). This adds a backwards-compatibility path that allows old files to continue to use the old algorithm, while using the new and improved algorithm with new files.

src/Mod/Sketcher/App/SketchObject.cpp

@@ -117,6 +117,11 @@ SketchObject::SketchObject() : geoLastId(0)
                       "Internal Geometry",
                       App::Prop_None,
                       "Enables selection of closed profiles within a sketch as input for operations");
+    ADD_PROPERTY_TYPE(_ExternalGeoVersion,
+                      (0),
+                      "Compatibility",
+                      (App::PropertyType)(App::Prop_Hidden | App::Prop_ReadOnly),
+                      "Version of external geometry projection algorithm");
 
     Geometry.setOrderRelevant(true);
 
@@ -167,6 +172,7 @@ void SketchObject::setupObject()
             "User parameter:BaseApp/Preferences/Mod/Sketcher");
     ArcFitTolerance.setValue(hGrpp->GetFloat("ArcFitTolerance", Precision::Confusion()*10.0));
     MakeInternals.setValue(hGrpp->GetBool("MakeInternals", false));
+    _ExternalGeoVersion.setValue(1);
     inherited::setupObject();
 }
 

src/Mod/Sketcher/App/SketchObject.h

@@ -109,6 +109,7 @@ public:
     Part ::PropertyPartShape InternalShape;
     App ::PropertyPrecision InternalTolerance;
     App ::PropertyBool MakeInternals;
+    App ::PropertyInteger _ExternalGeoVersion;
     /** @name methods override Feature */
     //@{
     short mustExecute() const override;

src/Mod/Sketcher/App/SketchObjectExternal.cpp

@@ -1637,7 +1637,8 @@ void processEdge(const TopoDS_Edge& edge,
                  const gp_Pln& sketchPlane,
                  const Base::Rotation& invRot,
                  gp_Ax3& sketchAx3,
-                 TopoDS_Shape& aProjFace)
+                 TopoDS_Shape& aProjFace,
+                 int externalGeoVersion = 1)
 {
     using std::numbers::pi;
 
@@ -1990,8 +1991,11 @@ void processEdge(const TopoDS_Edge& edge,
         auto shape = Part::TopoShape(edge);
         bool planar = shape.findPlane(plane);
 
-        // Check if the edge is planar and plane is perpendicular to the projection plane
-        if (planar && plane.Axis().IsNormal(sketchPlane.Axis(), Precision::Angular())) {
+        // Check if the edge is planar and plane is perpendicular to the projection plane.
+        // The getBoundBoxOptimal approach (version >= 1) produces better results for new
+        // sketches, but old files (version 0) must use NormalProjection to preserve element maps.
+        if (externalGeoVersion >= 1
+            && planar && plane.Axis().IsNormal(sketchPlane.Axis(), Precision::Angular())) {
             // Project an edge to a line. Only works if the edge is planar and its plane is
             // perpendicular to the projection plane. OCC has trouble handling
             // BSpline projection to a straight line. Although it does correctly projects
@@ -2194,7 +2198,8 @@ void processFace (const Rotation& invRot,
                   gp_Ax3& sketchAx3,
                   TopoDS_Shape& aProjFace,
                   std::vector<std::unique_ptr<Part::Geometry>>& geos,
-                  TopoDS_Shape& refSubShape)
+                  TopoDS_Shape& refSubShape,
+                  int externalGeoVersion = 1)
 {
     const TopoDS_Face& face = TopoDS::Face(refSubShape);
     BRepAdaptor_Surface surface(face);
@@ -2209,7 +2214,7 @@ void processFace (const Rotation& invRot,
         for (edgeExp.Init(face, TopAbs_EDGE); edgeExp.More(); edgeExp.Next()) {
             TopoDS_Edge edge = TopoDS::Edge(edgeExp.Current());
             // Process each edge
-            processEdge(edge, geos, gPlane, invPlm, mov, sketchPlane, invRot, sketchAx3, aProjFace);
+            processEdge(edge, geos, gPlane, invPlm, mov, sketchPlane, invRot, sketchAx3, aProjFace, externalGeoVersion);
         }
 
         if (fabs(dnormal.Angle(snormal) - std::numbers::pi/2) < Precision::Confusion()) {
@@ -2295,6 +2300,8 @@ void SketchObject::rebuildExternalGeometry(std::optional<ExternalToAdd> extToAdd
 {
     Base::StateLocker lock(managedoperation, true); // no need to check input data validity as this is an sketchobject managed operation.
 
+    int extGeoVersion = _ExternalGeoVersion.getValue();
+
     fixMissingAxisInExternalGeo();
 
     // Analyze the state of existing external geometries to infer the desired state for new ones.
@@ -2528,11 +2535,11 @@ void SketchObject::rebuildExternalGeometry(std::optional<ExternalToAdd> extToAdd
             if (projection && !refSubShape.IsNull()) {
                 switch (refSubShape.ShapeType()) {
                 case TopAbs_FACE: {
-                    processFace(invRot, invPlm, mov, sketchPlane, gPlane, sketchAx3, aProjFace, geos, refSubShape);
+                    processFace(invRot, invPlm, mov, sketchPlane, gPlane, sketchAx3, aProjFace, geos, refSubShape, extGeoVersion);
                 } break;
                 case TopAbs_EDGE: {
                     const TopoDS_Edge& edge = TopoDS::Edge(refSubShape);
-                    processEdge(edge, geos, gPlane, invPlm, mov, sketchPlane, invRot, sketchAx3, aProjFace);
+                    processEdge(edge, geos, gPlane, invPlm, mov, sketchPlane, invRot, sketchAx3, aProjFace, extGeoVersion);
                 } break;
                 case TopAbs_VERTEX: {
                     importVertex(refSubShape);
@@ -2560,7 +2567,7 @@ void SketchObject::rebuildExternalGeometry(std::optional<ExternalToAdd> extToAdd
                 auto edges = intersectionShape.getSubTopoShapes(TopAbs_EDGE);
                 for (const auto& s : edges) {
                     TopoDS_Edge edge = TopoDS::Edge(s.getShape());
-                    processEdge(edge, geos, gPlane, invPlm, mov, sketchPlane, invRot, sketchAx3, aProjFace);
+                    processEdge(edge, geos, gPlane, invPlm, mov, sketchPlane, invRot, sketchAx3, aProjFace, extGeoVersion);
                 }
                 // Section of some face (e.g. sphere) produce more than one arcs
                 // from the same circle. So we try to fit the arcs with a single