Fix weld edges into faces splicing verts that shared a face

This could happen with degenerate faces.

1 files changed, 29 insertions, 6 deletions

diff --git a/source/blender/editors/mesh/editmesh_intersect.c b/source/blender/editors/mesh/editmesh_intersect.c
index d61e3279491..2c173a20eac 100644
--- a/source/blender/editors/mesh/editmesh_intersect.c
+++ b/source/blender/editors/mesh/editmesh_intersect.c
@@ -373,6 +373,26 @@ static void bm_face_split_by_edges(
 	}
 }
 
+/**
+ * Check if a vert is in any of the faces connected to the edge,
+ * \a f_ignore is a face we happen to know isn't shared by the vertex.
+ */
+static bool bm_vert_in_faces_radial(BMVert *v, BMEdge *e_radial, BMFace *f_ignore)
+{
+	BLI_assert(BM_vert_in_face(v, f_ignore) == false);
+	if (e_radial->l) {
+		BMLoop *l_iter = e_radial->l;
+		do {
+			if (l_iter->f != f_ignore) {
+				if (BM_vert_in_face(v, l_iter->f)) {
+					return true;
+				}
+			}
+		} while ((l_iter = l_iter->radial_next) != e_radial->l);
+	}
+	return false;
+}
+
 #ifdef USE_NET_ISLAND_CONNECT
 
 struct LinkBase {
@@ -791,12 +811,15 @@ static int edbm_face_split_by_edges_exec(bContext *C, wmOperator *UNUSED(op))
 							        v_pivot_co, &v_pivot_fac);
 
 							if (e_split) {
-								BMEdge *e_new;
-								BMVert *v_new = BM_edge_split(bm, e_split, e_split->v1, &e_new, v_pivot_fac);
-								if (v_new) {
-									/* we _know_ these don't share an edge */
-									BM_vert_splice(bm, v_pivot, v_new);
-									BM_elem_index_set(e_new, BM_elem_index_get(e_split));
+								/* for degenerate cases this vertex may be in one of this edges radial faces */
+								if (!bm_vert_in_faces_radial(v_pivot, e_split, f)) {
+									BMEdge *e_new;
+									BMVert *v_new = BM_edge_split(bm, e_split, e_split->v1, &e_new, v_pivot_fac);
+									if (v_new) {
+										/* we _know_ these don't share an edge */
+										BM_vert_splice(bm, v_pivot, v_new);
+										BM_elem_index_set(e_new, BM_elem_index_get(e_split));
+									}
 								}
 							}
 						}