From 07805f1a6149cdec4c4a2c20bc292b9ca6cdcdcf Mon Sep 17 00:00:00 2001
From: tomate44 <cg@grellier.fr>
Date: Tue, 26 Jul 2022 14:58:28 +0200
Subject: [PATCH] [Part] BSplineSurface: fix KnotSequence for periodic BSpline
 surfaces

---
 src/Mod/Part/App/BSplineSurfacePyImp.cpp | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/Mod/Part/App/BSplineSurfacePyImp.cpp b/src/Mod/Part/App/BSplineSurfacePyImp.cpp
index e848695282..7e7f593a6a 100644
--- a/src/Mod/Part/App/BSplineSurfacePyImp.cpp
+++ b/src/Mod/Part/App/BSplineSurfacePyImp.cpp
@@ -1641,8 +1641,14 @@ Py::List BSplineSurfacePy::getUKnotSequence(void) const
     Handle(Geom_BSplineSurface) surf = Handle(Geom_BSplineSurface)::DownCast
         (getGeometryPtr()->handle());
     Standard_Integer m = 0;
-    for (int i=1; i<= surf->NbUKnots(); i++)
-        m += surf->UMultiplicity(i);
+    if (surf->IsUPeriodic()) {
+        // knots=poles+2*degree-mult(1)+2
+        m = surf->NbUPoles() + 2*surf->UDegree() - surf->UMultiplicity(1) + 2;
+    }
+    else {
+        for (int i=1; i<= surf->NbUKnots(); i++)
+            m += surf->UMultiplicity(i);
+    }
     TColStd_Array1OfReal k(1,m);
     surf->UKnotSequence(k);
     Py::List list;
@@ -1657,8 +1663,14 @@ Py::List BSplineSurfacePy::getVKnotSequence(void) const
     Handle(Geom_BSplineSurface) surf = Handle(Geom_BSplineSurface)::DownCast
         (getGeometryPtr()->handle());
     Standard_Integer m = 0;
-    for (int i=1; i<= surf->NbVKnots(); i++)
-        m += surf->VMultiplicity(i);
+    if (surf->IsVPeriodic()) {
+        // knots=poles+2*degree-mult(1)+2
+        m = surf->NbVPoles() + 2*surf->VDegree() - surf->VMultiplicity(1) + 2;
+    }
+    else {
+        for (int i=1; i<= surf->NbVKnots(); i++)
+            m += surf->VMultiplicity(i);
+    }
     TColStd_Array1OfReal k(1,m);
     surf->VKnotSequence(k);
     Py::List list;