mesh_bsurfaces.py

            points_B.append(
                self.main_object.matrix_world @ self.main_object.data.vertices[verts_tips_parsed_idx[1]].co
                )
            points_B.append(
                self.main_object.matrix_world @ self.main_object.data.vertices[middle_vertex_idx].co
                )
            points_first_stroke_tips.append(
                self.main_splines.data.splines[0].bezier_points[0].co
                )
            points_first_stroke_tips.append(
                self.main_splines.data.splines[0].bezier_points[
                                                    len(self.main_splines.data.splines[0].bezier_points) - 1
                                                    ].co
                )

            angle_A = self.orientation_difference(points_A, points_first_stroke_tips)
            angle_B = self.orientation_difference(points_B, points_first_stroke_tips)

            if angle_A < angle_B:
                first_vert_U_idx = verts_tips_parsed_idx[0]
                first_vert_V_idx = verts_tips_parsed_idx[1]
            else:
                first_vert_U_idx = verts_tips_parsed_idx[1]
                first_vert_V_idx = verts_tips_parsed_idx[0]

        elif selection_type == "SINGLE" or selection_type == "TWO_NOT_CONNECTED":
            first_sketched_point_first_stroke_co = self.main_splines.data.splines[0].bezier_points[0].co
            last_sketched_point_first_stroke_co = \
                    self.main_splines.data.splines[0].bezier_points[
                                                    len(self.main_splines.data.splines[0].bezier_points) - 1
                                                    ].co
            first_sketched_point_last_stroke_co = \
                    self.main_splines.data.splines[
                                            len(self.main_splines.data.splines) - 1
                                            ].bezier_points[0].co
            if len(self.main_splines.data.splines) > 1:
                first_sketched_point_second_stroke_co = self.main_splines.data.splines[1].bezier_points[0].co
                last_sketched_point_second_stroke_co = \
                    self.main_splines.data.splines[1].bezier_points[
                                            len(self.main_splines.data.splines[1].bezier_points) - 1
                                            ].co

            single_unselected_neighbors = []  # Only the neighbors of the single unselected verts
            for verts_neig_idx in single_unselected_verts_and_neighbors:
                single_unselected_neighbors.append(verts_neig_idx[1])
                single_unselected_neighbors.append(verts_neig_idx[2])

            all_chains_tips_and_middle_vert = []
            for v_idx in all_chains_tips_idx:
                if v_idx not in single_unselected_neighbors:
                    all_chains_tips_and_middle_vert.append(v_idx)

            all_chains_tips_and_middle_vert += single_unselected_verts

            all_participating_verts = all_chains_tips_and_middle_vert + all_verts_idx

            # The tip of the selected vertices nearest to the first point of the first sketched stroke
            nearest_tip_to_first_st_first_pt_idx, shortest_distance_to_first_stroke = \
                    self.shortest_distance(
                                self.main_object,
                                first_sketched_point_first_stroke_co,
                                all_chains_tips_and_middle_vert
                                )
            # If the nearest tip is not from a closed selection, get the opposite tip vertex index
            if nearest_tip_to_first_st_first_pt_idx not in single_unselected_verts or \
               nearest_tip_to_first_st_first_pt_idx == middle_vertex_idx:

                nearest_tip_to_first_st_first_pt_opposite_idx = \
                    self.opposite_tip(
                                nearest_tip_to_first_st_first_pt_idx,
                                verts_tips_same_chain_idx
                                )
            # The tip of the selected vertices nearest to the last point of the first sketched stroke
            nearest_tip_to_first_st_last_pt_idx, _temp_dist = \
                    self.shortest_distance(
                                self.main_object,
                                last_sketched_point_first_stroke_co,
                                all_chains_tips_and_middle_vert
                                )
            # The tip of the selected vertices nearest to the first point of the last sketched stroke
            nearest_tip_to_last_st_first_pt_idx, shortest_distance_to_last_stroke = \
                    self.shortest_distance(
                                self.main_object,
                                first_sketched_point_last_stroke_co,
                                all_chains_tips_and_middle_vert
                                )
            if len(self.main_splines.data.splines) > 1:
                # The selected vertex nearest to the first point of the second sketched stroke
                # (This will be useful to determine the direction of the closed
                # selection V when extruding along strokes)
                nearest_vert_to_second_st_first_pt_idx, _temp_dist = \
                        self.shortest_distance(
                                self.main_object,
                                first_sketched_point_second_stroke_co,
                                all_verts_idx
                                )
                # The selected vertex nearest to the first point of the second sketched stroke
                # (This will be useful to determine the direction of the closed
                # selection V2 when extruding along strokes)
                nearest_vert_to_second_st_last_pt_idx, _temp_dist = \
                        self.shortest_distance(
                                self.main_object,
                                last_sketched_point_second_stroke_co,
                                all_verts_idx
                                )
            # Determine if the single selection will be treated as U or as V
            edges_sum = 0
            for i in all_selected_edges_idx:
                edges_sum += (
                    (self.main_object.matrix_world @
                     self.main_object.data.vertices[self.main_object.data.edges[i].vertices[0]].co) -
                    (self.main_object.matrix_world @
                     self.main_object.data.vertices[self.main_object.data.edges[i].vertices[1]].co)
                    ).length

            average_edge_length = edges_sum / len(all_selected_edges_idx)

            # Get shortest distance from the first point of the last stroke to any participating vertex
            _temp_idx, shortest_distance_to_last_stroke = \
                        self.shortest_distance(
                                self.main_object,
                                first_sketched_point_last_stroke_co,
                                all_participating_verts
                                )
            # If the beginning of the first stroke is near enough, and its orientation
            # difference with the first edge of the nearest selection chain is not too high,
            # interpret things as an "extrude along strokes" instead of "extrude through strokes"
            if shortest_distance_to_first_stroke < average_edge_length / 4 and \
             shortest_distance_to_last_stroke < average_edge_length and \
             len(self.main_splines.data.splines) > 1:

                self.selection_U_exists = False
                self.selection_V_exists = True
                # If the first selection is not closed
                if nearest_tip_to_first_st_first_pt_idx not in single_unselected_verts or \
                  nearest_tip_to_first_st_first_pt_idx == middle_vertex_idx:
                    self.selection_V_is_closed = False
                    closing_vert_U_idx = None
                    closing_vert_U2_idx = None
                    closing_vert_V_idx = None
                    closing_vert_V2_idx = None

                    first_vert_V_idx = nearest_tip_to_first_st_first_pt_idx

                    if selection_type == "TWO_NOT_CONNECTED":
                        self.selection_V2_exists = True

                        first_vert_V2_idx = nearest_tip_to_first_st_last_pt_idx
                else:
                    self.selection_V_is_closed = True
                    closing_vert_V_idx = nearest_tip_to_first_st_first_pt_idx

                    # Get the neighbors of the first (unselected) vert of the closed selection U.
                    vert_neighbors = []
                    for verts in single_unselected_verts_and_neighbors:
                        if verts[0] == nearest_tip_to_first_st_first_pt_idx:
                            vert_neighbors.append(verts[1])
                            vert_neighbors.append(verts[2])
                            break

                    verts_V = self.get_ordered_verts(
                                    self.main_object, all_selected_edges_idx,
                                    all_verts_idx, vert_neighbors[0], middle_vertex_idx, None
                                    )

                    for i in range(0, len(verts_V)):
                        if verts_V[i].index == nearest_vert_to_second_st_first_pt_idx:
                            # If the vertex nearest to the first point of the second stroke
                            # is in the first half of the selected verts
                            if i >= len(verts_V) / 2:
                                first_vert_V_idx = vert_neighbors[1]
                                break
                            else:
                                first_vert_V_idx = vert_neighbors[0]
                                break

                if selection_type == "TWO_NOT_CONNECTED":
                    self.selection_V2_exists = True
                    # If the second selection is not closed
                    if nearest_tip_to_first_st_last_pt_idx not in single_unselected_verts or \
                      nearest_tip_to_first_st_last_pt_idx == middle_vertex_idx:

                        self.selection_V2_is_closed = False
                        closing_vert_V2_idx = None
                        first_vert_V2_idx = nearest_tip_to_first_st_last_pt_idx

                    else:
                        self.selection_V2_is_closed = True
                        closing_vert_V2_idx = nearest_tip_to_first_st_last_pt_idx

                        # Get the neighbors of the first (unselected) vert of the closed selection U
                        vert_neighbors = []
                        for verts in single_unselected_verts_and_neighbors:
                            if verts[0] == nearest_tip_to_first_st_last_pt_idx:
                                vert_neighbors.append(verts[1])
                                vert_neighbors.append(verts[2])
                                break

                        verts_V2 = self.get_ordered_verts(
                                        self.main_object, all_selected_edges_idx,
                                        all_verts_idx, vert_neighbors[0], middle_vertex_idx, None
                                        )

                        for i in range(0, len(verts_V2)):
                            if verts_V2[i].index == nearest_vert_to_second_st_last_pt_idx:
                                # If the vertex nearest to the first point of the second stroke
                                # is in the first half of the selected verts
                                if i >= len(verts_V2) / 2:
                                    first_vert_V2_idx = vert_neighbors[1]
                                    break
                                else:
                                    first_vert_V2_idx = vert_neighbors[0]
                                    break
                else:
                    self.selection_V2_exists = False

            else:
                self.selection_U_exists = True
                self.selection_V_exists = False
                # If the first selection is not closed
                if nearest_tip_to_first_st_first_pt_idx not in single_unselected_verts or \
                  nearest_tip_to_first_st_first_pt_idx == middle_vertex_idx:
                    self.selection_U_is_closed = False
                    closing_vert_U_idx = None

                    points_tips = []
                    points_tips.append(
                            self.main_object.matrix_world @
                            self.main_object.data.vertices[nearest_tip_to_first_st_first_pt_idx].co
                            )
                    points_tips.append(
                            self.main_object.matrix_world @
                            self.main_object.data.vertices[nearest_tip_to_first_st_first_pt_opposite_idx].co
                            )
                    points_first_stroke_tips = []
                    points_first_stroke_tips.append(self.main_splines.data.splines[0].bezier_points[0].co)
                    points_first_stroke_tips.append(
                        self.main_splines.data.splines[0].bezier_points[
                                                len(self.main_splines.data.splines[0].bezier_points) - 1
                                                ].co
                        )
                    vec_A = points_tips[0] - points_tips[1]
                    vec_B = points_first_stroke_tips[0] - points_first_stroke_tips[1]

                    # Compare the direction of the selection and the first
                    # grease pencil stroke to determine which is the "first" vertex of the selection
                    if vec_A.dot(vec_B) < 0:
                        first_vert_U_idx = nearest_tip_to_first_st_first_pt_opposite_idx
                    else:
                        first_vert_U_idx = nearest_tip_to_first_st_first_pt_idx

                else:
                    self.selection_U_is_closed = True
                    closing_vert_U_idx = nearest_tip_to_first_st_first_pt_idx

                    # Get the neighbors of the first (unselected) vert of the closed selection U
                    vert_neighbors = []
                    for verts in single_unselected_verts_and_neighbors:
                        if verts[0] == nearest_tip_to_first_st_first_pt_idx:
                            vert_neighbors.append(verts[1])
                            vert_neighbors.append(verts[2])
                            break

                    points_first_and_neighbor = []
                    points_first_and_neighbor.append(
                            self.main_object.matrix_world @
                            self.main_object.data.vertices[nearest_tip_to_first_st_first_pt_idx].co
                            )
                    points_first_and_neighbor.append(
                            self.main_object.matrix_world @
                            self.main_object.data.vertices[vert_neighbors[0]].co
                            )
                    points_first_stroke_tips = []
                    points_first_stroke_tips.append(self.main_splines.data.splines[0].bezier_points[0].co)
                    points_first_stroke_tips.append(self.main_splines.data.splines[0].bezier_points[1].co)

                    vec_A = points_first_and_neighbor[0] - points_first_and_neighbor[1]
                    vec_B = points_first_stroke_tips[0] - points_first_stroke_tips[1]

                    # Compare the direction of the selection and the first grease pencil stroke to
                    # determine which is the vertex neighbor to the first vertex (unselected) of
                    # the closed selection. This will determine the direction of the closed selection
                    if vec_A.dot(vec_B) < 0:
                        first_vert_U_idx = vert_neighbors[1]
                    else:
                        first_vert_U_idx = vert_neighbors[0]

                if selection_type == "TWO_NOT_CONNECTED":
                    self.selection_U2_exists = True
                    # If the second selection is not closed
                    if nearest_tip_to_last_st_first_pt_idx not in single_unselected_verts or \
                      nearest_tip_to_last_st_first_pt_idx == middle_vertex_idx:

                        self.selection_U2_is_closed = False
                        closing_vert_U2_idx = None
                        first_vert_U2_idx = nearest_tip_to_last_st_first_pt_idx
                    else:
                        self.selection_U2_is_closed = True
                        closing_vert_U2_idx = nearest_tip_to_last_st_first_pt_idx

                        # Get the neighbors of the first (unselected) vert of the closed selection U
                        vert_neighbors = []
                        for verts in single_unselected_verts_and_neighbors:
                            if verts[0] == nearest_tip_to_last_st_first_pt_idx:
                                vert_neighbors.append(verts[1])
                                vert_neighbors.append(verts[2])
                                break

                        points_first_and_neighbor = []
                        points_first_and_neighbor.append(
                                self.main_object.matrix_world @
                                self.main_object.data.vertices[nearest_tip_to_last_st_first_pt_idx].co
                                )
                        points_first_and_neighbor.append(
                                self.main_object.matrix_world @
                                self.main_object.data.vertices[vert_neighbors[0]].co
                                )
                        points_last_stroke_tips = []
                        points_last_stroke_tips.append(
                                self.main_splines.data.splines[
                                                        len(self.main_splines.data.splines) - 1
                                                        ].bezier_points[0].co
                                )
                        points_last_stroke_tips.append(
                                self.main_splines.data.splines[
                                                        len(self.main_splines.data.splines) - 1
                                                        ].bezier_points[1].co
                                )
                        vec_A = points_first_and_neighbor[0] - points_first_and_neighbor[1]
                        vec_B = points_last_stroke_tips[0] - points_last_stroke_tips[1]

                        # Compare the direction of the selection and the last grease pencil stroke to
                        # determine which is the vertex neighbor to the first vertex (unselected) of
                        # the closed selection. This will determine the direction of the closed selection
                        if vec_A.dot(vec_B) < 0:
                            first_vert_U2_idx = vert_neighbors[1]
                        else:
                            first_vert_U2_idx = vert_neighbors[0]
                else:
                    self.selection_U2_exists = False

        elif selection_type == "NO_SELECTION":
            self.selection_U_exists = False
            self.selection_V_exists = False

        # Get an ordered list of the vertices of Selection-U
        verts_ordered_U = []
        if self.selection_U_exists:
            verts_ordered_U = self.get_ordered_verts(
                                    self.main_object, all_selected_edges_idx,
                                    all_verts_idx, first_vert_U_idx,
                                    middle_vertex_idx, closing_vert_U_idx
                                    )

        # Get an ordered list of the vertices of Selection-U2
        verts_ordered_U2 = []
        if self.selection_U2_exists:
            verts_ordered_U2 = self.get_ordered_verts(
                                    self.main_object, all_selected_edges_idx,
                                    all_verts_idx, first_vert_U2_idx,
                                    middle_vertex_idx, closing_vert_U2_idx
                                    )

        # Get an ordered list of the vertices of Selection-V
        verts_ordered_V = []
        if self.selection_V_exists:
            verts_ordered_V = self.get_ordered_verts(
                                    self.main_object, all_selected_edges_idx,
                                    all_verts_idx, first_vert_V_idx,
                                    middle_vertex_idx, closing_vert_V_idx
                                    )
            verts_ordered_V_indices = [x.index for x in verts_ordered_V]

        # Get an ordered list of the vertices of Selection-V2
        verts_ordered_V2 = []
        if self.selection_V2_exists:
            verts_ordered_V2 = self.get_ordered_verts(
                                    self.main_object, all_selected_edges_idx,
                                    all_verts_idx, first_vert_V2_idx,
                                    middle_vertex_idx, closing_vert_V2_idx
                                    )

        # Check if when there are two-not-connected selections both have the same
        # number of verts. If not terminate the script
        if ((self.selection_U2_exists and len(verts_ordered_U) != len(verts_ordered_U2)) or
           (self.selection_V2_exists and len(verts_ordered_V) != len(verts_ordered_V2))):
            # Display a warning
            self.report({'WARNING'}, "Both selections must have the same number of edges")

            self.stopping_errors = True

            return{'CANCELLED'}

        # Calculate edges U proportions
        # Sum selected edges U lengths
        edges_lengths_U = []
        edges_lengths_sum_U = 0

        if self.selection_U_exists:
            edges_lengths_U, edges_lengths_sum_U = self.get_chain_length(
                                                            self.main_object,
                                                            verts_ordered_U
                                                            )
        if self.selection_U2_exists:
            edges_lengths_U2, edges_lengths_sum_U2 = self.get_chain_length(
                                                            self.main_object,
                                                            verts_ordered_U2
                                                            )
        # Sum selected edges V lengths
        edges_lengths_V = []
        edges_lengths_sum_V = 0

        if self.selection_V_exists:
            edges_lengths_V, edges_lengths_sum_V = self.get_chain_length(
                                                            self.main_object,
                                                            verts_ordered_V
                                                            )
        if self.selection_V2_exists:
            edges_lengths_V2, edges_lengths_sum_V2 = self.get_chain_length(
                                                            self.main_object,
                                                            verts_ordered_V2
                                                            )

        bpy.ops.object.editmode_toggle('INVOKE_REGION_WIN')
        bpy.ops.curve.subdivide('INVOKE_REGION_WIN',
                                number_cuts=bpy.context.scene.bsurfaces.SURFSK_precision)
        bpy.ops.object.editmode_toggle('INVOKE_REGION_WIN')

        # Proportions U
        edges_proportions_U = []
        edges_proportions_U = self.get_edges_proportions(
                                    edges_lengths_U, edges_lengths_sum_U,
                                    self.selection_U_exists, self.edges_U
                                    )
        verts_count_U = len(edges_proportions_U) + 1

        if self.selection_U2_exists:
            edges_proportions_U2 = []
            edges_proportions_U2 = self.get_edges_proportions(
                                    edges_lengths_U2, edges_lengths_sum_U2,
                                    self.selection_U2_exists, self.edges_V
                                    )

        # Proportions V
        edges_proportions_V = []
        edges_proportions_V = self.get_edges_proportions(
                                    edges_lengths_V, edges_lengths_sum_V,
                                    self.selection_V_exists, self.edges_V
                                    )

        if self.selection_V2_exists:
            edges_proportions_V2 = []
            edges_proportions_V2 = self.get_edges_proportions(
                                    edges_lengths_V2, edges_lengths_sum_V2,
                                    self.selection_V2_exists, self.edges_V
                                    )

        # Cyclic Follow: simplify sketched curves, make them Cyclic, and complete
        # the actual sketched curves with a "closing segment"
        if self.cyclic_follow and not self.selection_V_exists and not \
          ((self.selection_U_exists and not self.selection_U_is_closed) or
          (self.selection_U2_exists and not self.selection_U2_is_closed)):

            simplified_spline_coords = []
            simplified_curve = []
            ob_simplified_curve = []
            splines_first_v_co = []
            for i in range(len(self.main_splines.data.splines)):
                # Create a curve object for the actual spline "cyclic extension"
                simplified_curve.append(bpy.data.curves.new('SURFSKIO_simpl_crv', 'CURVE'))
                ob_simplified_curve.append(bpy.data.objects.new('SURFSKIO_simpl_crv', simplified_curve[i]))
                bpy.context.collection.objects.link(ob_simplified_curve[i])

                simplified_curve[i].dimensions = "3D"

                spline_coords = []
                for bp in self.main_splines.data.splines[i].bezier_points:
                    spline_coords.append(bp.co)

                # Simplification
                simplified_spline_coords.append(self.simplify_spline(spline_coords, 5))

                # Get the coordinates of the first vert of the actual spline
                splines_first_v_co.append(simplified_spline_coords[i][0])

                # Generate the spline
                spline = simplified_curve[i].splines.new('BEZIER')
                # less one because one point is added when the spline is created
                spline.bezier_points.add(len(simplified_spline_coords[i]) - 1)
                for p in range(0, len(simplified_spline_coords[i])):
                    spline.bezier_points[p].co = simplified_spline_coords[i][p]

                spline.use_cyclic_u = True

                spline_bp_count = len(spline.bezier_points)

                bpy.ops.object.select_all('INVOKE_REGION_WIN', action='DESELECT')
                ob_simplified_curve[i].select_set(True)
                bpy.context.view_layer.objects.active = ob_simplified_curve[i]

                bpy.ops.object.editmode_toggle('INVOKE_REGION_WIN')
                bpy.ops.curve.select_all('INVOKE_REGION_WIN', action='SELECT')
                bpy.ops.curve.handle_type_set('INVOKE_REGION_WIN', type='AUTOMATIC')
                bpy.ops.curve.select_all('INVOKE_REGION_WIN', action='DESELECT')
                bpy.ops.object.editmode_toggle('INVOKE_REGION_WIN')

                # Select the "closing segment", and subdivide it
                ob_simplified_curve[i].data.splines[0].bezier_points[0].select_control_point = True
                ob_simplified_curve[i].data.splines[0].bezier_points[0].select_left_handle = True
                ob_simplified_curve[i].data.splines[0].bezier_points[0].select_right_handle = True

                ob_simplified_curve[i].data.splines[0].bezier_points[spline_bp_count - 1].select_control_point = True
                ob_simplified_curve[i].data.splines[0].bezier_points[spline_bp_count - 1].select_left_handle = True
                ob_simplified_curve[i].data.splines[0].bezier_points[spline_bp_count - 1].select_right_handle = True

                bpy.ops.object.editmode_toggle('INVOKE_REGION_WIN')
                segments = sqrt(
                          (ob_simplified_curve[i].data.splines[0].bezier_points[0].co -
                           ob_simplified_curve[i].data.splines[0].bezier_points[spline_bp_count - 1].co).length /
                          self.average_gp_segment_length
                        )
                for t in range(2):
                    bpy.ops.curve.subdivide('INVOKE_REGION_WIN', number_cuts=segments)

                # Delete the other vertices and make it non-cyclic to
                # keep only the needed verts of the "closing segment"
                bpy.ops.curve.select_all(action='INVERT')
                bpy.ops.curve.delete(type='VERT')
                ob_simplified_curve[i].data.splines[0].use_cyclic_u = False
                bpy.ops.object.editmode_toggle('INVOKE_REGION_WIN')

                # Add the points of the "closing segment" to the original curve from grease pencil stroke
                first_new_index = len(self.main_splines.data.splines[i].bezier_points)
                self.main_splines.data.splines[i].bezier_points.add(
                                                    len(ob_simplified_curve[i].data.splines[0].bezier_points) - 1
                                                    )
                for t in range(1, len(ob_simplified_curve[i].data.splines[0].bezier_points)):
                    self.main_splines.data.splines[i].bezier_points[t - 1 + first_new_index].co = \
                            ob_simplified_curve[i].data.splines[0].bezier_points[t].co

                # Delete the temporal curve
                bpy.ops.object.delete({"selected_objects": [ob_simplified_curve[i]]})

        # Get the coords of the points distributed along the sketched strokes,
        # with proportions-U of the first selection
        pts_on_strokes_with_proportions_U = self.distribute_pts(
                                                    self.main_splines.data.splines,
                                                    edges_proportions_U
                                                    )
        sketched_splines_parsed = []

        if self.selection_U2_exists:
            # Initialize the multidimensional list with the proportions of all the segments
            proportions_loops_crossing_strokes = []
            for i in range(len(pts_on_strokes_with_proportions_U)):
                proportions_loops_crossing_strokes.append([])

                for t in range(len(pts_on_strokes_with_proportions_U[0])):
                    proportions_loops_crossing_strokes[i].append(None)

            # Calculate the proportions of each segment of the loops-U from pts_on_strokes_with_proportions_U
            for lp in range(len(pts_on_strokes_with_proportions_U[0])):
                loop_segments_lengths = []

                for st in range(len(pts_on_strokes_with_proportions_U)):
                    # When on the first stroke, add the segment from the selection to the dirst stroke
                    if st == 0:
                        loop_segments_lengths.append(
                                    ((self.main_object.matrix_world @ verts_ordered_U[lp].co) -
                                    pts_on_strokes_with_proportions_U[0][lp]).length
                                    )
                    # For all strokes except for the last, calculate the distance
                    # from the actual stroke to the next
                    if st != len(pts_on_strokes_with_proportions_U) - 1:
                        loop_segments_lengths.append(
                                    (pts_on_strokes_with_proportions_U[st][lp] -
                                    pts_on_strokes_with_proportions_U[st + 1][lp]).length
                                    )
                    # When on the last stroke, add the segments
                    # from the last stroke to the second selection
                    if st == len(pts_on_strokes_with_proportions_U) - 1:
                        loop_segments_lengths.append(
                                    (pts_on_strokes_with_proportions_U[st][lp] -
                                    (self.main_object.matrix_world @ verts_ordered_U2[lp].co)).length
                                    )
                # Calculate full loop length
                loop_seg_lengths_sum = 0
                for i in range(len(loop_segments_lengths)):
                    loop_seg_lengths_sum += loop_segments_lengths[i]

                # Fill the multidimensional list with the proportions of all the segments
                for st in range(len(pts_on_strokes_with_proportions_U)):
                    proportions_loops_crossing_strokes[st][lp] = \
                        loop_segments_lengths[st] / loop_seg_lengths_sum

            # Calculate proportions for each stroke
            for st in range(len(pts_on_strokes_with_proportions_U)):
                actual_stroke_spline = []
                # Needs to be a list for the "distribute_pts" method
                actual_stroke_spline.append(self.main_splines.data.splines[st])

                # Calculate the proportions for the actual stroke.
                actual_edges_proportions_U = []
                for i in range(len(edges_proportions_U)):
                    proportions_sum = 0

                    # Sum the proportions of this loop up to the actual.
                    for t in range(0, st + 1):
                        proportions_sum += proportions_loops_crossing_strokes[t][i]
                    # i + 1, because proportions_loops_crossing_strokes refers to loops,
                    # and the proportions refer to edges, so we start at the element 1
                    # of proportions_loops_crossing_strokes instead of element 0
                    actual_edges_proportions_U.append(
                            edges_proportions_U[i] -
                            ((edges_proportions_U[i] - edges_proportions_U2[i]) * proportions_sum)
                            )
                points_actual_spline = self.distribute_pts(actual_stroke_spline, actual_edges_proportions_U)
                sketched_splines_parsed.append(points_actual_spline[0])
        else:
            sketched_splines_parsed = pts_on_strokes_with_proportions_U

        # If the selection type is "TWO_NOT_CONNECTED" replace the
        # points of the last spline with the points in the "target" selection
        if selection_type == "TWO_NOT_CONNECTED":
            if self.selection_U2_exists:
                for i in range(0, len(sketched_splines_parsed[len(sketched_splines_parsed) - 1])):
                    sketched_splines_parsed[len(sketched_splines_parsed) - 1][i] = \
                            self.main_object.matrix_world @ verts_ordered_U2[i].co

        # Create temporary curves along the "control-points" found
        # on the sketched curves and the mesh selection
        mesh_ctrl_pts_name = "SURFSKIO_ctrl_pts"
        me = bpy.data.meshes.new(mesh_ctrl_pts_name)
        ob_ctrl_pts = bpy.data.objects.new(mesh_ctrl_pts_name, me)
        ob_ctrl_pts.data = me
        bpy.context.collection.objects.link(ob_ctrl_pts)

        cyclic_loops_U = []
        first_verts = []
        second_verts = []
        last_verts = []

        for i in range(0, verts_count_U):
            vert_num_in_spline = 1

            if self.selection_U_exists:
                ob_ctrl_pts.data.vertices.add(1)
                last_v = ob_ctrl_pts.data.vertices[len(ob_ctrl_pts.data.vertices) - 1]
                last_v.co = self.main_object.matrix_world @ verts_ordered_U[i].co

                vert_num_in_spline += 1

            for t in range(0, len(sketched_splines_parsed)):
                ob_ctrl_pts.data.vertices.add(1)
                v = ob_ctrl_pts.data.vertices[len(ob_ctrl_pts.data.vertices) - 1]
                v.co = sketched_splines_parsed[t][i]

                if vert_num_in_spline > 1:
                    ob_ctrl_pts.data.edges.add(1)
                    ob_ctrl_pts.data.edges[len(ob_ctrl_pts.data.edges) - 1].vertices[0] = \
                            len(ob_ctrl_pts.data.vertices) - 2
                    ob_ctrl_pts.data.edges[len(ob_ctrl_pts.data.edges) - 1].vertices[1] = \
                            len(ob_ctrl_pts.data.vertices) - 1

                if t == 0:
                    first_verts.append(v.index)

                if t == 1:
                    second_verts.append(v.index)

                if t == len(sketched_splines_parsed) - 1:
                    last_verts.append(v.index)

                last_v = v
                vert_num_in_spline += 1

        bpy.ops.object.select_all('INVOKE_REGION_WIN', action='DESELECT')
        ob_ctrl_pts.select_set(True)
        bpy.context.view_layer.objects.active = ob_ctrl_pts

        bpy.ops.object.editmode_toggle('INVOKE_REGION_WIN')
        bpy.ops.mesh.select_all(action='DESELECT')
        bpy.ops.object.editmode_toggle('INVOKE_REGION_WIN')

        # Determine which loops-U will be "Cyclic"
        for i in range(0, len(first_verts)):
            # When there is Cyclic Cross there is no need of
            # Automatic Join, (and there are at least three strokes)
            if self.automatic_join and not self.cyclic_cross and \
               selection_type != "TWO_CONNECTED" and len(self.main_splines.data.splines) >= 3:

                v = ob_ctrl_pts.data.vertices
                first_point_co = v[first_verts[i]].co
                second_point_co = v[second_verts[i]].co
                last_point_co = v[last_verts[i]].co

                # Coordinates of the point in the center of both the first and last verts.
                verts_center_co = [
                        (first_point_co[0] + last_point_co[0]) / 2,
                        (first_point_co[1] + last_point_co[1]) / 2,
                        (first_point_co[2] + last_point_co[2]) / 2
                        ]
                vec_A = second_point_co - first_point_co
                vec_B = second_point_co - Vector(verts_center_co)

                # Calculate the length of the first segment of the loop,
                # and the length it would have after moving the first vert
                # to the middle position between first and last
                length_original = (second_point_co - first_point_co).length
                length_target = (second_point_co - Vector(verts_center_co)).length

                angle = vec_A.angle(vec_B) / pi

                # If the target length doesn't stretch too much, and the
                # its angle doesn't change to much either
                if length_target <= length_original * 1.03 * self.join_stretch_factor and \
                   angle <= 0.008 * self.join_stretch_factor and not self.selection_U_exists:

                    cyclic_loops_U.append(True)
                    # Move the first vert to the center coordinates
                    ob_ctrl_pts.data.vertices[first_verts[i]].co = verts_center_co
                    # Select the last verts from Cyclic loops, for later deletion all at once
                    v[last_verts[i]].select = True
                else:
                    cyclic_loops_U.append(False)
            else:
                # If "Cyclic Cross" is active then "all" crossing curves become cyclic
                if self.cyclic_cross and not self.selection_U_exists and not \
                   ((self.selection_V_exists and not self.selection_V_is_closed) or
                   (self.selection_V2_exists and not self.selection_V2_is_closed)):

                    cyclic_loops_U.append(True)
                else:
                    cyclic_loops_U.append(False)

        # The cyclic_loops_U list needs to be reversed.
        cyclic_loops_U.reverse()

        # Delete the previously selected (last_)verts.
        bpy.ops.object.editmode_toggle('INVOKE_REGION_WIN')
        bpy.ops.mesh.delete('INVOKE_REGION_WIN', type='VERT')
        bpy.ops.object.editmode_toggle('INVOKE_REGION_WIN')

        # Create curves from control points.
        bpy.ops.object.convert('INVOKE_REGION_WIN', target='CURVE', keep_original=False)
        ob_curves_surf = bpy.context.view_layer.objects.active
        bpy.ops.object.editmode_toggle('INVOKE_REGION_WIN')
        bpy.ops.curve.spline_type_set('INVOKE_REGION_WIN', type='BEZIER')
        bpy.ops.curve.handle_type_set('INVOKE_REGION_WIN', type='AUTOMATIC')

        # Make Cyclic the splines designated as Cyclic.
        for i in range(0, len(cyclic_loops_U)):
            ob_curves_surf.data.splines[i].use_cyclic_u = cyclic_loops_U[i]

        # Get the coords of all points on first loop-U, for later comparison with its
        # subdivided version, to know which points of the loops-U are crossed by the
        # original strokes. The indices will be the same for the other loops-U
        if self.loops_on_strokes:
            coords_loops_U_control_points = []
            for p in ob_ctrl_pts.data.splines[0].bezier_points:
                coords_loops_U_control_points.append(["%.4f" % p.co[0], "%.4f" % p.co[1], "%.4f" % p.co[2]])

            tuple(coords_loops_U_control_points)

        # Calculate number of edges-V in case option "Loops on strokes" is active or inactive
        if self.loops_on_strokes and not self.selection_V_exists:
                edges_V_count = len(self.main_splines.data.splines) * self.edges_V
        else:
            edges_V_count = len(edges_proportions_V)

        # The Follow precision will vary depending on the number of Follow face-loops
        precision_multiplier = round(2 + (edges_V_count / 15))
        curve_cuts = bpy.context.scene.bsurfaces.SURFSK_precision * precision_multiplier

        # Subdivide the curves
        bpy.ops.curve.subdivide('INVOKE_REGION_WIN', number_cuts=curve_cuts)

        # The verts position shifting that happens with splines subdivision.
        # For later reorder splines points
        verts_position_shift = curve_cuts + 1
        bpy.ops.object.editmode_toggle('INVOKE_REGION_WIN')

        # Reorder coordinates of the points of each spline to put the first point of
        # the spline starting at the position it was the first point before sudividing
        # the curve. And make a new curve object per spline (to handle memory better later)
        splines_U_objects = []
        for i in range(len(ob_curves_surf.data.splines)):
            spline_U_curve = bpy.data.curves.new('SURFSKIO_spline_U_' + str(i), 'CURVE')
            ob_spline_U = bpy.data.objects.new('SURFSKIO_spline_U_' + str(i), spline_U_curve)
            bpy.context.collection.objects.link(ob_spline_U)

            spline_U_curve.dimensions = "3D"

            # Add points to the spline in the new curve object
            ob_spline_U.data.splines.new('BEZIER')
            for t in range(len(ob_curves_surf.data.splines[i].bezier_points)):
                if cyclic_loops_U[i] is True and not self.selection_U_exists:  # If the loop is cyclic
                    if t + verts_position_shift <= len(ob_curves_surf.data.splines[i].bezier_points) - 1:
                        point_index = t + verts_position_shift
                    else:
                        point_index = t + verts_position_shift - len(ob_curves_surf.data.splines[i].bezier_points)
                else:
                    point_index = t
                # to avoid adding the first point since it's added when the spline is created
                if t > 0:
                    ob_spline_U.data.splines[0].bezier_points.add(1)
                ob_spline_U.data.splines[0].bezier_points[t].co = \
                        ob_curves_surf.data.splines[i].bezier_points[point_index].co

            if cyclic_loops_U[i] is True and not self.selection_U_exists:  # If the loop is cyclic
                # Add a last point at the same location as the first one
                ob_spline_U.data.splines[0].bezier_points.add(1)
                ob_spline_U.data.splines[0].bezier_points[len(ob_spline_U.data.splines[0].bezier_points) - 1].co = \
                        ob_spline_U.data.splines[0].bezier_points[0].co
            else:
                ob_spline_U.data.splines[0].use_cyclic_u = False

            splines_U_objects.append(ob_spline_U)
            bpy.ops.object.select_all('INVOKE_REGION_WIN', action='DESELECT')
            ob_spline_U.select_set(True)
            bpy.context.view_layer.objects.active = ob_spline_U

        # When option "Loops on strokes" is active each "Cross" loop will have
        # its own proportions according to where the original strokes "touch" them
        if self.loops_on_strokes:
            # Get the indices of points where the original strokes "touch" loops-U
            points_U_crossed_by_strokes = []
            for i in range(len(splines_U_objects[0].data.splines[0].bezier_points)):
                bp = splines_U_objects[0].data.splines[0].bezier_points[i]
                if ["%.4f" % bp.co[0], "%.4f" % bp.co[1], "%.4f" % bp.co[2]] in coords_loops_U_control_points:
                    points_U_crossed_by_strokes.append(i)

            # Make a dictionary with the number of the edge, in the selected chain V, corresponding to each stroke
            edge_order_number_for_splines = {}
            if self.selection_V_exists:
                # For two-connected selections add a first hypothetic stroke at the beginning.
                if selection_type == "TWO_CONNECTED":
                    edge_order_number_for_splines[0] = 0

                for i in range(len(self.main_splines.data.splines)):
                    sp = self.main_splines.data.splines[i]
                    v_idx, _dist_temp = self.shortest_distance(
                                                self.main_object,
                                                sp.bezier_points[0].co,
                                                verts_ordered_V_indices
                                                )
                    # Get the position (edges count) of the vert v_idx in the selected chain V
                    edge_idx_in_chain = verts_ordered_V_indices.index(v_idx)

                    # For two-connected selections the strokes go after the
                    # hypothetic stroke added before, so the index adds one per spline
                    if selection_type == "TWO_CONNECTED":
                        spline_number = i + 1
                    else:
                        spline_number = i

                    edge_order_number_for_splines[spline_number] = edge_idx_in_chain

                    # Get the first and last verts indices for later comparison
                    if i == 0:
                        first_v_idx = v_idx
                    elif i == len(self.main_splines.data.splines) - 1:
                        last_v_idx = v_idx

                if self.selection_V_is_closed:
                    # If there is no last stroke on the last vertex (same as first vertex),
                    # add a hypothetic spline at last vert order
                    if first_v_idx != last_v_idx:
                        edge_order_number_for_splines[(len(self.main_splines.data.splines) - 1) + 1] = \
                                len(verts_ordered_V_indices) - 1
                    else:
                        if self.cyclic_cross:
                            edge_order_number_for_splines[len(self.main_splines.data.splines) - 1] = \
                                    len(verts_ordered_V_indices) - 2
                            edge_order_number_for_splines[(len(self.main_splines.data.splines) - 1) + 1] = \
                                    len(verts_ordered_V_indices) - 1
                        else:
                            edge_order_number_for_splines[len(self.main_splines.data.splines) - 1] = \
                                    len(verts_ordered_V_indices) - 1

        # Get the coords of the points distributed along the
        # "crossing curves", with appropriate proportions-V
        surface_splines_parsed = []
        for i in range(len(splines_U_objects)):
            sp_ob = splines_U_objects[i]
            # If "Loops on strokes" option is active, calculate the proportions for each loop-U
            if self.loops_on_strokes:
                # Segments distances from stroke to stroke
                dist = 0
                full_dist = 0
                segments_distances = []
                for t in range(len(sp_ob.data.splines[0].bezier_points)):
                    bp = sp_ob.data.splines[0].bezier_points[t]

                    if t == 0:
                        last_p = bp.co
                    else:
                        actual_p = bp.co
                        dist += (last_p - actual_p).length

                        if t in points_U_crossed_by_strokes:
                            segments_distances.append(dist)
                            full_dist += dist

                            dist = 0

                        last_p = actual_p

                # Calculate Proportions.
                used_edges_proportions_V = []
                for t in range(len(segments_distances)):
                    if self.selection_V_exists:
                        if t == 0:
                            order_number_last_stroke = 0

                        segment_edges_length_V = 0
                        segment_edges_length_V2 = 0
                        for order in range(order_number_last_stroke, edge_order_number_for_splines[t + 1]):
                            segment_edges_length_V += edges_lengths_V[order]
                            if self.selection_V2_exists:
                                segment_edges_length_V2 += edges_lengths_V2[order]

                        for order in range(order_number_last_stroke, edge_order_number_for_splines[t + 1]):
                            # Calculate each "sub-segment" (the ones between each stroke) length
                            if self.selection_V2_exists:
                                proportion_sub_seg = (edges_lengths_V2[order] -
                                    ((edges_lengths_V2[order] - edges_lengths_V[order]) /
                                    len(splines_U_objects) * i)) / (segment_edges_length_V2 -
                                    (segment_edges_length_V2 - segment_edges_length_V) /
                                    len(splines_U_objects) * i)

                                sub_seg_dist = segments_distances[t] * proportion_sub_seg
                            else:
                                proportion_sub_seg = edges_lengths_V[order] / segment_edges_length_V
                                sub_seg_dist = segments_distances[t] * proportion_sub_seg

                            used_edges_proportions_V.append(sub_seg_dist / full_dist)

                        order_number_last_stroke = edge_order_number_for_splines[t + 1]

                    else:
                        for _c in range(self.edges_V):
                            # Calculate each "sub-segment" (the ones between each stroke) length
                            sub_seg_dist = segments_distances[t] / self.edges_V
                            used_edges_proportions_V.append(sub_seg_dist / full_dist)

                actual_spline = self.distribute_pts(sp_ob.data.splines, used_edges_proportions_V)
                surface_splines_parsed.append(actual_spline[0])

            else:
                if self.selection_V2_exists:
                    used_edges_proportions_V = []
                    for p in range(len(edges_proportions_V)):
                        used_edges_proportions_V.append(
                                    edges_proportions_V2[p] -
                                    ((edges_proportions_V2[p] -
                                    edges_proportions_V[p]) / len(splines_U_objects) * i)
                                    )
                else:
                    used_edges_proportions_V = edges_proportions_V

                actual_spline = self.distribute_pts(sp_ob.data.splines, used_edges_proportions_V)
                surface_splines_parsed.append(actual_spline[0])

        # Set the verts of the first and last splines to the locations
        # of the respective verts in the selections
        if self.selection_V_exists:
            for i in range(0, len(surface_splines_parsed[0])):
                surface_splines_parsed[len(surface_splines_parsed) - 1][i] = \
                        self.main_object.matrix_world @ verts_ordered_V[i].co

        if selection_type == "TWO_NOT_CONNECTED":
            if self.selection_V2_exists:
                for i in range(0, len(surface_splines_parsed[0])):
                    surface_splines_parsed[0][i] = self.main_object.matrix_world @ verts_ordered_V2[i].co

        # When "Automatic join" option is active (and the selection type != "TWO_CONNECTED"),
        # merge the verts of the tips of the loops when they are "near enough"
        if self.automatic_join and selection_type != "TWO_CONNECTED":
            # Join the tips of "Follow" loops that are near enough and must be "closed"
            if not self.selection_V_exists and len(edges_proportions_U) >= 3:
                for i in range(len(surface_splines_parsed[0])):
                    sp = surface_splines_parsed
                    loop_segment_dist = (sp[0][i] - sp[1][i]).length

                    verts_middle_position_co = [
                            (sp[0][i][0] + sp[len(sp) - 1][i][0]) / 2,
                            (sp[0][i][1] + sp[len(sp) - 1][i][1]) / 2,
                            (sp[0][i][2] + sp[len(sp) - 1][i][2]) / 2
                            ]
                    points_original = []
                    points_original.append(sp[1][i])
                    points_original.append(sp[0][i])

                    points_target = []
                    points_target.append(sp[1][i])
                    points_target.append(Vector(verts_middle_position_co))

                    vec_A = points_original[0] - points_original[1]
                    vec_B = points_target[0] - points_target[1]