From e6b3f6ccef662428a3c909c4f3769111333067f3 Mon Sep 17 00:00:00 2001
From: Noisyfox <timemanager.rick@gmail.com>
Date: Sat, 9 May 2026 21:47:40 +0800
Subject: [PATCH] Add option to keep existing painting while mapping new
 paintings to it

---
 src/libslic3r/Model.cpp            | 10 +++++++---
 src/libslic3r/Model.hpp            |  4 ++--
 src/libslic3r/TriangleSelector.cpp |  7 ++++++-
 src/libslic3r/TriangleSelector.hpp |  4 +++-
 4 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/src/libslic3r/Model.cpp b/src/libslic3r/Model.cpp
index 586043bf4b..000ab997a9 100644
--- a/src/libslic3r/Model.cpp
+++ b/src/libslic3r/Model.cpp
@@ -1995,7 +1995,7 @@ std::optional<TriangleSelector::SavedPainting> ModelVolume::save_painting() cons
     return {};
 }
 
-void ModelVolume::restore_painting(const std::optional<TriangleSelector::SavedPainting>& saved)
+void ModelVolume::restore_painting(const std::optional<TriangleSelector::SavedPainting>& saved, const bool keep_existing_paint)
 {
     if (!saved) {
         return;
@@ -2005,9 +2005,13 @@ void ModelVolume::restore_painting(const std::optional<TriangleSelector::SavedPa
                          FacetsAnnotation& target_facets) {
         if (src_data.bitstream.empty())
             return;
-        auto result = TriangleSelector::remap_painting(saved->mesh.its, src_data, mesh().its, Geometry::translation_transform(mesh().get_init_shift()));
+        auto result =
+            TriangleSelector::remap_painting(saved->mesh.its, src_data, mesh().its, Geometry::translation_transform(mesh().get_init_shift()),
+                                             keep_existing_paint ?
+                                                 std::optional<std::reference_wrapper<const TriangleSelector::TriangleSplittingData>>{std::ref(target_facets.get_data())} :
+                                                 std::optional<std::reference_wrapper<const TriangleSelector::TriangleSplittingData>>{});
         if (!result.bitstream.empty())
-            target_facets.set_data(result);
+            target_facets.set_data(std::move(result));
     };
     remap_one(saved->supported, supported_facets);
     remap_one(saved->seam,      seam_facets);
diff --git a/src/libslic3r/Model.hpp b/src/libslic3r/Model.hpp
index fbe8da7b6a..d8697adb41 100644
--- a/src/libslic3r/Model.hpp
+++ b/src/libslic3r/Model.hpp
@@ -731,7 +731,7 @@ public:
     void assign(const FacetsAnnotation &rhs) { if (! this->timestamp_matches(rhs)) { m_data = rhs.m_data; this->copy_timestamp(rhs); } }
     void assign(FacetsAnnotation &&rhs) { if (! this->timestamp_matches(rhs)) { m_data = std::move(rhs.m_data); this->copy_timestamp(rhs); } }
     const TriangleSelector::TriangleSplittingData &get_data() const noexcept { return m_data; }
-    void set_data(const TriangleSelector::TriangleSplittingData &data) { m_data = data; this->touch(); }
+    void set_data(TriangleSelector::TriangleSplittingData &&data) { m_data = std::move(data); this->touch(); }
     bool set(const TriangleSelector& selector);
     indexed_triangle_set get_facets(const ModelVolume& mv, EnforcerBlockerType type) const;
     // BBS
@@ -884,7 +884,7 @@ public:
     std::optional<TriangleSelector::SavedPainting> save_painting() const;
     
     // Remap painting data from previous saved source to this mesh
-    void restore_painting(const std::optional<TriangleSelector::SavedPainting>& saved);
+    void restore_painting(const std::optional<TriangleSelector::SavedPainting>& saved, bool keep_existing_paint = false);
 
     // BBS: quick access for volume extruders, 1 based
     mutable std::vector<int> mmuseg_extruders;
diff --git a/src/libslic3r/TriangleSelector.cpp b/src/libslic3r/TriangleSelector.cpp
index 19f638a160..0fb1423df4 100644
--- a/src/libslic3r/TriangleSelector.cpp
+++ b/src/libslic3r/TriangleSelector.cpp
@@ -2407,7 +2407,8 @@ TriangleSelector::TriangleSplittingData TriangleSelector::remap_painting(
     const indexed_triangle_set& source_its,
     const TriangleSplittingData& source_painting,
     const indexed_triangle_set& target_its,
-    const Transform3d& target_transform)
+    const Transform3d& target_transform,
+    const std::optional<std::reference_wrapper<const TriangleSplittingData>>& existing_painting)
 {
     TriangleSelector::TriangleSplittingData result;
     if (source_painting.bitstream.empty())
@@ -2477,6 +2478,10 @@ TriangleSelector::TriangleSplittingData TriangleSelector::remap_painting(
 
     // 4. For each painted face, we find the nearest target face, and apply the TriangleCursor to paint it
     TriangleSelector target_selector(target_mesh);
+    if (existing_painting) {
+        // Restore existing painting first, if given
+        target_selector.deserialize(existing_painting->get(), false);
+    }
     for (auto tri_ref : painted_triangles) {
         const Triangle& tri = tri_ref.get();
         const Vec3f& pv0    = source_selector.m_vertices[tri.verts_idxs[0]].v;
diff --git a/src/libslic3r/TriangleSelector.hpp b/src/libslic3r/TriangleSelector.hpp
index 412c9fb9b1..09b606b5d2 100644
--- a/src/libslic3r/TriangleSelector.hpp
+++ b/src/libslic3r/TriangleSelector.hpp
@@ -383,11 +383,13 @@ public:
 
     // Remap painting data from source mesh to target mesh using spatial mapping.
     // `target_transform` should transform the target mesh into source's coordinate space.
+    // If `existing_painting` is present, the result will be a combine of `existing_painting` and remapped `source_painting`.
     static TriangleSplittingData remap_painting(
         const indexed_triangle_set& source_its,
         const TriangleSplittingData& source_painting,
         const indexed_triangle_set& target_its,
-        const Transform3d& target_transform);
+        const Transform3d& target_transform,
+        const std::optional<std::reference_wrapper<const TriangleSplittingData>>& existing_painting);
 
 protected:
     // Triangle and info about how it's split.