diff --git a/src/libslic3r/PrintObject.cpp b/src/libslic3r/PrintObject.cpp
index 68cb0f6be9..befa80233b 100644
--- a/src/libslic3r/PrintObject.cpp
+++ b/src/libslic3r/PrintObject.cpp
@@ -2798,6 +2798,10 @@ static void project_triangles_to_slabs(ConstLayerPtrsAdaptor layers, const index
 void PrintObject::project_and_append_custom_facets(
         bool seam, EnforcerBlockerType type, std::vector<Polygons>& out) const
 {
+    // BBS: Approve adding enforcer support on vertical faces
+    SlabSlicingConfig config;
+    config.isVertical = true;
+
     for (const ModelVolume* mv : this->model_object()->volumes)
         if (mv->is_model_part()) {
             const indexed_triangle_set custom_facets = seam
@@ -2811,7 +2815,7 @@ void PrintObject::project_and_append_custom_facets(
                 else {
                     std::vector<Polygons> projected;
                     // Support blockers or enforcers. Project downward facing painted areas upwards to their respective slicing plane.
-                    slice_mesh_slabs(custom_facets, zs_from_layers(this->layers()), this->trafo_centered() * mv->get_matrix(), nullptr, &projected, [](){});
+                    slice_mesh_slabs(custom_facets, zs_from_layers(this->layers()), this->trafo_centered() * mv->get_matrix(), nullptr, &projected, [](){}, config);
                     // Merge these projections with the output, layer by layer.
                     assert(! projected.empty());
                     assert(out.empty() || out.size() == projected.size());
diff --git a/src/libslic3r/TriangleMeshSlicer.cpp b/src/libslic3r/TriangleMeshSlicer.cpp
index 6182dfe641..29f6a8f856 100644
--- a/src/libslic3r/TriangleMeshSlicer.cpp
+++ b/src/libslic3r/TriangleMeshSlicer.cpp
@@ -753,7 +753,9 @@ inline std::pair<SlabLines, SlabLines> slice_slabs_make_lines(
     const std::vector<float>                        &zs,
     bool                                             top,
     bool                                             bottom,
-    const ThrowOnCancel                              throw_on_cancel_fn)
+    const ThrowOnCancel                              throw_on_cancel_fn,
+    // BBS: solve conflicts (see declaration) and most elegant way I can get
+    SlabSlicingConfig                                config)
 {
     std::pair<SlabLines, SlabLines> out;
     SlabLines   &lines_top      = out.first;
@@ -772,7 +774,7 @@ inline std::pair<SlabLines, SlabLines> slice_slabs_make_lines(
 
     tbb::parallel_for(
         tbb::blocked_range<int>(0, int(indices.size())),
-        [&vertices, &indices, &face_neighbors, &face_edge_ids, num_edges, &face_orientation, &zs, top, bottom, &lines_top, &lines_bottom, &lines_mutex_top, &lines_mutex_bottom, throw_on_cancel_fn]
+        [&vertices, &indices, &face_neighbors, &face_edge_ids, num_edges, &face_orientation, &zs, top, bottom, &lines_top, &lines_bottom, &lines_mutex_top, &lines_mutex_bottom, throw_on_cancel_fn, &config]
         (const tbb::blocked_range<int> &range) {
             for (int face_idx = range.begin(); face_idx < range.end(); ++ face_idx) {
                 if ((face_idx & 0x0ffff) == 0)
@@ -790,7 +792,8 @@ inline std::pair<SlabLines, SlabLines> slice_slabs_make_lines(
                         }
                     slice_facet_with_slabs<true>(vertices, indices, face_idx, neighbors, edge_ids, num_edges, zs, lines_top, lines_mutex_top);
                 }
-                if (bottom && (fo == FaceOrientation::Down || fo == FaceOrientation::Degenerate)) {
+                // BBS: add vertical faces option
+                if (bottom && (fo == FaceOrientation::Down || (config.isVertical && fo == FaceOrientation::Vertical) || fo == FaceOrientation::Degenerate)) {
                     Vec3i neighbors = face_neighbors[face_idx];
                     // Reset neighborship of this triangle in case the other triangle is oriented backwards from this one.
                     for (int i = 0; i < 3; ++ i)
@@ -1895,7 +1898,8 @@ void slice_mesh_slabs(
     const Transform3d                &trafo,
     std::vector<Polygons>            *out_top,
     std::vector<Polygons>            *out_bottom,
-    std::function<void()>             throw_on_cancel)
+    std::function<void()>             throw_on_cancel,
+    SlabSlicingConfig                config)
 {
     BOOST_LOG_TRIVIAL(debug) << "slice_mesh_slabs to polygons";
 
@@ -1974,7 +1978,7 @@ void slice_mesh_slabs(
     std::vector<Vec3i> face_edge_ids  = its_face_edge_ids(mesh, face_neighbors, true, &num_edges);
     std::pair<SlabLines, SlabLines> lines = slice_slabs_make_lines(
         vertices_transformed, mesh.indices, face_neighbors, face_edge_ids, num_edges, face_orientation, zs, 
-        out_top != nullptr, out_bottom != nullptr, throw_on_cancel);
+        out_top != nullptr, out_bottom != nullptr, throw_on_cancel, config);
 
     throw_on_cancel();
 
diff --git a/src/libslic3r/TriangleMeshSlicer.hpp b/src/libslic3r/TriangleMeshSlicer.hpp
index 1a8b643629..603e95e78e 100644
--- a/src/libslic3r/TriangleMeshSlicer.hpp
+++ b/src/libslic3r/TriangleMeshSlicer.hpp
@@ -46,6 +46,19 @@ struct MeshSlicingParamsEx : public MeshSlicingParams
     double        resolution { 0 };
 };
 
+// BBS: MusangKing - NEW: add paint-on support on vertical-faces
+// this SlabSlicingConfig aiming to distinguish if slice_slabs_make_lines() outputs lines by slab_slicing on vertical faces
+// e.g., for support enforcer operation: isVertical = true; for other color painting operations: isVertical = false (default).
+// solve conflicts STUDIO-1183/970/1285
+struct SlabSlicingConfig
+{
+    SlabSlicingConfig()
+        : isVertical(false)
+    {}
+
+    bool isVertical;
+};
+
 // All the following slicing functions shall produce consistent results with the same mesh, same transformation matrix and slicing parameters.
 // Namely, slice_mesh_slabs() shall produce consistent results with slice_mesh() and slice_mesh_ex() in the sense, that projections made by 
 // slice_mesh_slabs() shall fall onto slicing planes produced by slice_mesh().
@@ -107,7 +120,9 @@ void slice_mesh_slabs(
     const Transform3d                &trafo,
     std::vector<Polygons>            *out_top,
     std::vector<Polygons>            *out_bottom,
-    std::function<void()>             throw_on_cancel);
+    std::function<void()>             throw_on_cancel,
+    // BBS: MusangKing
+    SlabSlicingConfig                config = SlabSlicingConfig());
 
 // Project mesh upwards pointing surfaces / downwards pointing surfaces into 2D polygons.
 void project_mesh(