New utility function its_merge_vertices().

Implemented contour simplification inside slice_mesh_ex().

src/libslic3r/TriangleMesh.hpp

@@ -98,10 +98,19 @@ std::vector<std::vector<size_t>> create_vertex_faces_index(const indexed_triangl
 // Used for chaining slice lines into polygons.
 std::vector<Vec3i> create_face_neighbors_index(const indexed_triangle_set &its);
 std::vector<Vec3i> create_face_neighbors_index(const indexed_triangle_set &its, std::function<void()> throw_on_cancel_callback);
+
+// Merge duplicate vertices, return number of vertices removed.
+// This function will happily create non-manifolds if more than two faces share the same vertex position
+// or more than two faces share the same edge position!
+int its_merge_vertices(indexed_triangle_set &its, bool shrink_to_fit = true);
+
 // Remove degenerate faces, return number of faces removed.
 int its_remove_degenerate_faces(indexed_triangle_set &its, bool shrink_to_fit = true);
+
 // Remove vertices, which none of the faces references. Return number of freed vertices.
 int its_compactify_vertices(indexed_triangle_set &its, bool shrink_to_fit = true);
+
+// Shrink the vectors of its.vertices and its.faces to a minimum size by reallocating the two vectors.
 void its_shrink_to_fit(indexed_triangle_set &its);
 
 TriangleMesh make_cube(double x, double y, double z);