bmesh api function: BM_edge_face_tangent()

was used by inset but make into an api function since scripts can use this too.

source/blender/bmesh/intern/bmesh_queries.c

@@ -812,6 +812,31 @@ float BM_edge_face_angle(BMEdge *e)
 	}
 }
 
+/**
+ * \brief BMESH EDGE/FACE TANGENT
+ *
+ * Calculate the tangent at this loop corner or fallback to the face normal on straignt lines.
+ * This vector always points inward into the face.
+ *
+ * \brief BM_edge_face_tangent
+ * \param e
+ * \param e_loop The loop to calculate the tangent at,
+ * used to get the face and winding direction.
+ */
+
+void BM_edge_face_tangent(BMEdge *e, BMLoop *e_loop, float r_tangent[3])
+{
+	float tvec[3];
+	BMVert *v1, *v2;
+	BM_edge_ordered_verts_ex(e, &v1, &v2, e_loop);
+
+	sub_v3_v3v3(tvec, v1->co, v2->co); /* use for temp storage */
+	/* note, we could average the tangents of both loops,
+	 * for non flat ngons it will give a better direction */
+	cross_v3_v3v3(r_tangent, tvec, e_loop->f->no);
+	normalize_v3(r_tangent);
+}
+
 /**
  * \brief BMESH VERT/EDGE ANGLE
  *

source/blender/bmesh/intern/bmesh_queries.h

@@ -62,6 +62,8 @@ void    BM_loop_face_normal(BMLoop *l, float r_normal[3]);
 void    BM_loop_face_tangent(BMLoop *l, float r_tangent[3]);
 
 float   BM_edge_face_angle(BMEdge *e);
+void    BM_edge_face_tangent(BMEdge *e, BMLoop *e_loop, float r_tangent[3]);
+
 float   BM_vert_edge_angle(BMVert *v);
 
 BMEdge *BM_edge_exists(BMVert *v1, BMVert *v2);

source/blender/bmesh/operators/bmo_inset.c

@@ -42,17 +42,6 @@ typedef struct SplitEdgeInfo {
 	BMLoop *l;
 } SplitEdgeInfo;
 
-static void edge_loop_tangent(BMEdge *e, BMLoop *e_loop, float r_no[3])
-{
-	float tvec[3];
-	BMVert *v1, *v2;
-	BM_edge_ordered_verts_ex(e, &v1, &v2, e_loop);
-
-	sub_v3_v3v3(tvec, v1->co, v2->co); /* use for temp storage */
-	cross_v3_v3v3(r_no, tvec, e_loop->f->no);
-	normalize_v3(r_no);
-}
-
 /**
  * return the tag loop where there is...
  * - only 1 tagged face attached to this edge.
@@ -188,7 +177,7 @@ void bmo_inset_exec(BMesh *bm, BMOperator *op)
 
 		/* calc edge-split info */
 		es->e_new = es->l->e;
-		edge_loop_tangent(es->e_new, es->l, es->no);
+		BM_edge_face_tangent(es->e_new, es->l, es->no);
 
 		if (es->e_new == es->e_old) { /* happens on boundary edges */
 			/* take care here, we're creating this double edge which _must_ have its verts replaced later on */

source/blender/python/bmesh/bmesh_py_types.c

@@ -1243,6 +1243,36 @@ static PyObject *bpy_bmedge_calc_face_angle(BPy_BMEdge *self)
 	return PyFloat_FromDouble(BM_edge_face_angle(self->e));
 }
 
+PyDoc_STRVAR(bpy_bmedge_calc_tangent_doc,
+".. method:: calc_tangent(loop)\n"
+"\n"
+"   Return the tangent at this edge relative to a face (pointing inward into the face).\n"
+"   This uses the face normal for calculation.\n"
+"\n"
+"   :arg loop: The loop used for tangent calculation.\n"
+"   :type loop: :class:`BMLoop`\n"
+"   :return: a normalized vector.\n"
+"   :rtype: :class:`mathutils.Vector`\n"
+);
+static PyObject *bpy_bmedge_calc_tangent(BPy_BMEdge *self, PyObject *args)
+{
+	BPy_BMLoop *py_loop;
+	BPY_BM_CHECK_OBJ(self);
+
+	if (!PyArg_ParseTuple(args, "O!:BMEdge.calc_face_tangent",
+	                      &BPy_BMLoop_Type, &py_loop))
+	{
+		return NULL;
+	}
+	else {
+		float vec[3];
+		BPY_BM_CHECK_OBJ(py_loop);
+		/* no need to check if they are from the same mesh or even connected */
+		BM_edge_face_tangent(self->e, py_loop->l, vec);
+		return Vector_CreatePyObject(vec, 3, Py_NEW, NULL);
+	}
+}
+
 
 PyDoc_STRVAR(bpy_bmedge_other_vert_doc,
 ".. method:: other_vert(vert)\n"
@@ -2080,6 +2110,7 @@ static struct PyMethodDef bpy_bmedge_methods[] = {
 
     {"calc_length",     (PyCFunction)bpy_bmedge_calc_length,     METH_NOARGS,  bpy_bmedge_calc_length_doc},
     {"calc_face_angle", (PyCFunction)bpy_bmedge_calc_face_angle, METH_NOARGS,  bpy_bmedge_calc_face_angle_doc},
+    {"calc_tangent",    (PyCFunction)bpy_bmedge_calc_tangent,    METH_VARARGS, bpy_bmedge_calc_tangent_doc},
 
     {"normal_update",  (PyCFunction)bpy_bmedge_normal_update,  METH_NOARGS,  bpy_bmedge_normal_update_doc},