fix: ruled/extrude surface u/v parameter swap in grid layout

src/curves/nurbs_operations.cpp

@@ -360,30 +360,26 @@ NurbsSurface extrude_curve(const NurbsCurve& curve,
     Vector3D dir_n = direction.normalized();
     Vector3D offset = dir_n * length;
 
-    std::vector<std::vector<Point3D>> grid(2);
-    std::vector<std::vector<double>> w(2);
-    grid[0] = cp;
-    grid[1].reserve(n);
-    w[0] = weights;
-    w[1].reserve(n);
-
+    // Build control grid as grid[u][v]: u=curve direction, v=extrusion direction
+    std::vector<std::vector<Point3D>> grid(n);
+    std::vector<std::vector<double>> w(n);
     for (int i = 0; i < n; ++i) {
-        grid[1].push_back(Point3D(
-            cp[i].x() + offset.x(),
-            cp[i].y() + offset.y(),
-            cp[i].z() + offset.z()
-        ));
-        w[1].push_back(i < static_cast<int>(weights.size()) ? weights[i] : 1.0);
+        grid[i] = {
+            cp[i],
+            Point3D(cp[i].x() + offset.x(),
+                    cp[i].y() + offset.y(),
+                    cp[i].z() + offset.z())
+        };
+        double wi = i < static_cast<int>(weights.size()) ? weights[i] : 1.0;
+        w[i] = {wi, wi};
     }
 
-    // v-knots: linear degree-1 in extrusion direction
-    // u-knots: inherit from curve
     return NurbsSurface(grid,
-                         {0.0, 0.0, 1.0, 1.0},  // v-direction knots (degree 1)
-                         curve.knots(),           // u-direction knots
+                         curve.knots(),            // ku — u-direction knots from profile curve
+                         {0.0, 0.0, 1.0, 1.0},   // kv — v-direction knots (linear extrusion)
                          w,
-                         1,                        // degree_v = 1 (linear extrusion)
-                         curve.degree());          // degree_u = curve's degree
+                         curve.degree(),           // du — curve degree in u-direction
+                         1);                       // dv — linear in v-direction
 }
 
 } // namespace vde::curves

src/curves/nurbs_surface.cpp

@@ -78,15 +78,21 @@ Vector3D NurbsSurface::normal(double u, double v) const {
 }
 
 NurbsSurface NurbsSurface::ruled(const NurbsCurve& c1, const NurbsCurve& c2) {
-    std::vector<std::vector<Point3D>> grid(2);
+    // Build grid[u_index][v_index]: u along curve1->curve2, v along curves
     const auto& cp1 = c1.control_points();
     const auto& cp2 = c2.control_points();
-    grid[0] = cp1;
-    grid[1] = cp2;
-    std::vector<std::vector<double>> w(2);
-    w[0] = c1.weights();
-    w[1] = c2.weights();
-    return NurbsSurface(grid, {0,0,1,1}, c1.knots(), w, 1, c1.degree());
+    int n = static_cast<int>(cp1.size());
+    const auto& w1 = c1.weights();
+    const auto& w2 = c2.weights();
+    std::vector<std::vector<Point3D>> grid(n);
+    std::vector<std::vector<double>> w(n);
+    for (int i = 0; i < n; ++i) {
+        grid[i] = {cp1[i], cp2[i]};
+        double wi = i < static_cast<int>(w1.size()) ? w1[i] : 1.0;
+        double wij = i < static_cast<int>(w2.size()) ? w2[i] : 1.0;
+        w[i] = {wi, wij};
+    }
+    return NurbsSurface(grid, c1.knots(), {0,0,1,1}, w, c1.degree(), 1);
 }
 
 NurbsSurface NurbsSurface::revolve(const NurbsCurve& profile,