From 57fa3e44f475dfc39c24df59786ea0786d121dfa Mon Sep 17 00:00:00 2001
From: Ajinkya Dahale <AjinkyaDahale@users.noreply.github.com>
Date: Wed, 21 Sep 2022 20:23:30 +0530
Subject: [PATCH] [Sketcher] [planegcs] Evaluate lower degree B-spline factors

---
 src/Mod/Sketcher/App/planegcs/Geo.cpp | 18 +++++++++---------
 src/Mod/Sketcher/App/planegcs/Geo.h   |  7 +++++--
 2 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/src/Mod/Sketcher/App/planegcs/Geo.cpp b/src/Mod/Sketcher/App/planegcs/Geo.cpp
index 74dbc6a7d0..acf1442d81 100644
--- a/src/Mod/Sketcher/App/planegcs/Geo.cpp
+++ b/src/Mod/Sketcher/App/planegcs/Geo.cpp
@@ -712,7 +712,7 @@ BSpline* BSpline::Copy()
     return crv;
 }
 
-double BSpline::getLinCombFactor(double x, size_t k, size_t i)
+double BSpline::getLinCombFactor(double x, size_t k, size_t i, size_t p)
 {
     // Adapted to C++ from the python implementation in the Wikipedia page for de Boor algorithm
     // https://en.wikipedia.org/wiki/De_Boor%27s_algorithm.
@@ -727,23 +727,23 @@ double BSpline::getLinCombFactor(double x, size_t k, size_t i)
     if (flattenedknots.empty())
         setupFlattenedKnots();
 
-    std::vector d(degree + 1, 0.0);
+    std::vector d(p + 1, 0.0);
     // Ensure this is within range
-    int idxOfPole = static_cast<int>(i) + degree - static_cast<int>(k);
-    if (idxOfPole < 0 || idxOfPole > degree)
+    int idxOfPole = static_cast<int>(i) + p - static_cast<int>(k);
+    if (idxOfPole < 0 || idxOfPole > static_cast<int>(p))
         return 0.0;
     d[idxOfPole] = 1.0;
 
-    for (size_t r = 1; static_cast<int>(r) < degree + 1; ++r) {
-        for (size_t j = degree; j > r - 1; --j) {
+    for (size_t r = 1; static_cast<int>(r) < p + 1; ++r) {
+        for (size_t j = p; j > r - 1; --j) {
             double alpha =
-                (x - flattenedknots[j + k - degree]) /
-                (flattenedknots[j + 1 + k - r] - flattenedknots[j + k - degree]);
+                (x - flattenedknots[j + k - p]) /
+                (flattenedknots[j + 1 + k - r] - flattenedknots[j + k - p]);
             d[j] = (1.0 - alpha) * d[j-1] + alpha * d[j];
         }
     }
 
-    return d[degree];
+    return d[p];
 }
 
 void BSpline::setupFlattenedKnots()
diff --git a/src/Mod/Sketcher/App/planegcs/Geo.h b/src/Mod/Sketcher/App/planegcs/Geo.h
index 13ad0d4969..8de749312a 100644
--- a/src/Mod/Sketcher/App/planegcs/Geo.h
+++ b/src/Mod/Sketcher/App/planegcs/Geo.h
@@ -300,10 +300,13 @@ namespace GCS
         void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt) override;
         BSpline* Copy() override;
         /// finds the value B_i(x) such that spline(x) = sum(poles[i] * B_i(x))
-        /// i is index of control point
         /// x is the point at which combination is needed
         /// k is the range in `flattenedknots` that contains x
-        double getLinCombFactor(double x, size_t k, size_t i);
+        /// i is index of control point
+        /// p is the degree
+        double getLinCombFactor(double x, size_t k, size_t i, size_t p);
+        inline double getLinCombFactor(double x, size_t k, size_t i)
+        { return getLinCombFactor(x, k, i, degree); }
         void setupFlattenedKnots();
     };