1 files changed, 12 insertions, 0 deletions
diff --git a/src/2geom/sbasis-geometric.cpp b/src/2geom/sbasis-geometric.cpp
index 28e9fc964..c37118402 100644
--- a/src/2geom/sbasis-geometric.cpp
+++ b/src/2geom/sbasis-geometric.cpp
@@ -740,6 +740,18 @@ Geom::cubics_with_prescribed_curvature(Point const &M0,   Point const &M1,
     return cubics_fitting_curvature(M0,M1,dM0,dM1,d2M0xdM0,d2M1xdM1,insist_on_speed_signs,epsilon);
 }
 
+
+/**
+* \brief returns all the parameter values of A whose tangent passes through P.
+*/
+std::vector<double> find_tangents(Point P, D2<SBasis> const &A) {
+    SBasis crs (cross(A - P, derivative(A)));
+    crs = shift(crs*Linear(-1, 0)*Linear(-1, 0), -2); // We know that there is a double root at t=0 so we divide out t^2
+// JFB points out that this is equivalent to (t-1)^2 followed by a divide by s^2 (shift)
+    return roots(crs);
+}
+
+
 //}; // namespace