From ea5119ec3f89af6334d8ec3723fb87456d5a277d Mon Sep 17 00:00:00 2001
From: Noisyfox <timemanager.rick@gmail.com>
Date: Mon, 11 May 2026 15:33:09 +0800
Subject: [PATCH] Remap paint after contour cut (cut with part assigned to
 other side using right mouse click)

---
 src/libslic3r/CutUtils.cpp           | 19 ++++++++++++++++---
 src/libslic3r/CutUtils.hpp           |  2 +-
 src/slic3r/GUI/Gizmos/GLGizmoCut.cpp |  4 ++--
 3 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/src/libslic3r/CutUtils.cpp b/src/libslic3r/CutUtils.cpp
index d192a854bb..5899313035 100644
--- a/src/libslic3r/CutUtils.cpp
+++ b/src/libslic3r/CutUtils.cpp
@@ -454,7 +454,7 @@ static void merge_solid_parts_inside_object(ModelObjectPtrs& objects)
 }
 
 
-const ModelObjectPtrs& Cut::perform_by_contour(std::vector<Part> parts, int dowels_count)
+const ModelObjectPtrs& Cut::perform_by_contour(const ModelObject* src_object, std::vector<Part> parts, int dowels_count)
 {
     ModelObject* cut_mo = m_model.objects.front();
 
@@ -469,6 +469,19 @@ const ModelObjectPtrs& Cut::perform_by_contour(std::vector<Part> parts, int dowe
         lower->name = lower->name + "_B";
     }
 
+    // Save painting data so we later can remap it.
+    std::vector<std::optional<TriangleSelector::SavedPainting>> saved_paintings;
+    if (m_attributes.has(ModelObjectCutAttribute::KeepPaint)) {
+        const auto instance_matrix = src_object->instances[m_instance]->get_transformation().get_matrix_no_offset();
+        for (const auto volume : src_object->volumes) {
+            saved_paintings.emplace_back(volume->save_painting());
+            if (saved_paintings.back()) {
+                // Transform mesh to cut space (same transform as process_volume_cut applies)
+                saved_paintings.back()->mesh.transform(instance_matrix * volume->get_matrix(), true);
+            }
+        }
+    }
+
     const size_t cut_parts_cnt = parts.size();
     bool has_modifiers = false;
 
@@ -498,7 +511,7 @@ const ModelObjectPtrs& Cut::perform_by_contour(std::vector<Part> parts, int dowe
         merge_solid_parts_inside_object(cut_object_ptrs);
 
         // replace initial objects in model with cut object 
-        finalize(cut_object_ptrs, {});
+        finalize(cut_object_ptrs, saved_paintings);
     }
     else if (volumes.size() > cut_parts_cnt) {
         // Means that object is cut with connectors
@@ -529,7 +542,7 @@ const ModelObjectPtrs& Cut::perform_by_contour(std::vector<Part> parts, int dowe
         merge_solid_parts_inside_object(cut_object_ptrs);
 
         // replace initial objects in model with cut object
-        finalize(cut_object_ptrs, {});
+        finalize(cut_object_ptrs, saved_paintings);
 
         // Add Dowel-connectors as separate objects to model
         if (cut_connectors_obj.size() >= 3)
diff --git a/src/libslic3r/CutUtils.hpp b/src/libslic3r/CutUtils.hpp
index d7e486beaf..99cdb9cd65 100644
--- a/src/libslic3r/CutUtils.hpp
+++ b/src/libslic3r/CutUtils.hpp
@@ -56,7 +56,7 @@ public:
     };
 
     const ModelObjectPtrs& perform_with_plane();
-    const ModelObjectPtrs& perform_by_contour(std::vector<Part> parts, int dowels_count);
+    const ModelObjectPtrs& perform_by_contour(const ModelObject* src_object, std::vector<Part> parts, int dowels_count);
     const ModelObjectPtrs& perform_with_groove(const Groove& groove, const Transform3d& rotation_m, bool keep_as_parts = false);
 
 }; // namespace Cut
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoCut.cpp b/src/slic3r/GUI/Gizmos/GLGizmoCut.cpp
index da523788b8..f042656ab7 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoCut.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoCut.cpp
@@ -1908,7 +1908,7 @@ GLGizmoCut3D::PartSelection::PartSelection(const ModelObject* mo, const Transfor
     // split to parts
     for (int id = int(volumes.size())-1; id >= 0; id--)
         if (volumes[id]->is_splittable())
-            volumes[id]->split(1, false); // TODO: fix this
+            volumes[id]->split(1, false); // No need to remap paint here, we do it later in perform_by_contour
 
     m_parts.clear();
     for (const ModelVolume* volume : volumes) {
@@ -3337,7 +3337,7 @@ void GLGizmoCut3D::perform_cut(const Selection& selection)
         update_object_cut_id(cut_mo->cut_id, attributes, dowels_count);
 
         Cut cut(cut_mo, instance_idx, get_cut_matrix(selection), attributes);
-        const ModelObjectPtrs& new_objects = cut_by_contour    ? cut.perform_by_contour(m_part_selection.get_cut_parts(), dowels_count):
+        const ModelObjectPtrs& new_objects = cut_by_contour    ? cut.perform_by_contour(mo, m_part_selection.get_cut_parts(), dowels_count):
                                              cut_with_groove   ? cut.perform_with_groove(m_groove, m_rotation_m) :
                                                                  cut.perform_with_plane();