Implement correct centroid in DecomposedShape

src/libslic3r/Arrange/Core/NFP/Kernels/GravityKernel.hpp

@@ -19,7 +19,7 @@ struct GravityKernel {
     template<class ArrItem>
     double placement_fitness(const ArrItem &itm, const Vec2crd &transl) const
     {
-        Vec2d center = unscaled(envelope_bounding_box(itm).center());
+        Vec2d center = unscaled(envelope_centroid(itm));
 
         center += unscaled(transl);
 

src/libslic3r/Arrange/Core/NFP/Kernels/TMArrangeKernel.hpp

@@ -65,6 +65,8 @@ public:
         // Candidate item bounding box
         auto ibb = envelope_bounding_box(item);
         ibb.translate(transl);
+        auto itmcntr = envelope_centroid(item);
+        itmcntr += transl;
 
         // Calculate the full bounding box of the pile with the candidate item
         auto fullbb = m_pilebb;
@@ -115,7 +117,7 @@ public:
 
         switch (compute_case) {
         case WIPE_TOWER: {
-            score = (unscaled(ibb.center()) - unscaled(active_sink)).squaredNorm();
+            score = (unscaled(itmcntr) - unscaled(active_sink)).squaredNorm();
             break;
         }
         case BIG_ITEM: {
@@ -132,7 +134,7 @@ public:
             auto cc = fullbb.center(); // The gravity center
             dists[0] = (minc - cc).cast<double>().norm();
             dists[1] = (maxc - cc).cast<double>().norm();
-            dists[2] = (ibb.center() - cc).template cast<double>().norm();
+            dists[2] = (itmcntr - cc).template cast<double>().norm();
             dists[3] = (top_left - cc).cast<double>().norm();
             dists[4] = (bottom_right - cc).cast<double>().norm();
 
@@ -191,7 +193,7 @@ public:
             break;
         }
         case LAST_BIG_ITEM: {
-            score = norm((ibb.center() - m_pilebb.center()).template cast<double>().norm());
+            score = norm((itmcntr - m_pilebb.center()).template cast<double>().norm());
             break;
         }
         case SMALL_ITEM: {
@@ -199,7 +201,7 @@ public:
             // already processed bigger items.
             // No need to play around with the anchor points, the center will be
             // just fine for small items
-            score = norm((ibb.center() - bigbb.center()).template cast<double>().norm());
+            score = norm((itmcntr - bigbb.center()).template cast<double>().norm());
             break;
         }
         }

src/libslic3r/Arrange/Core/NFP/NFPArrangeItemTraits.hpp

@@ -74,6 +74,16 @@ template<class ArrItem, class En = void> struct NFPArrangeItemTraits_
     {
         return std::array{0.};
     }
+
+    static Vec2crd fixed_centroid(const ArrItem &itm)
+    {
+        return fixed_bounding_box(itm).center();
+    }
+
+    static Vec2crd envelope_centroid(const ArrItem &itm)
+    {
+        return envelope_bounding_box(itm).center();
+    }
 };
 
 template<class T>
@@ -137,6 +147,16 @@ template<class ArrItem> double fixed_area(const ArrItem &itm)
     return NFPArrangeItemTraits<ArrItem>::fixed_area(itm);
 }
 
+template<class ArrItem> Vec2crd fixed_centroid(const ArrItem &itm)
+{
+    return NFPArrangeItemTraits<ArrItem>::fixed_centroid(itm);
+}
+
+template<class ArrItem> Vec2crd envelope_centroid(const ArrItem &itm)
+{
+    return NFPArrangeItemTraits<ArrItem>::envelope_centroid(itm);
+}
+
 template<class ArrItem>
 auto allowed_rotations(const ArrItem &itm)
 {

src/libslic3r/Arrange/Items/ArrangeItem.cpp

@@ -13,6 +13,8 @@ namespace Slic3r { namespace arr2 {
 
 const Polygons &DecomposedShape::transformed_outline() const
 {
+    constexpr auto sc = scaled<double>(1.) * scaled<double>(1.);
+
     if (!m_transformed_outline_valid) {
         m_transformed_outline = contours();
         for (Polygon &poly : m_transformed_outline) {
@@ -20,7 +22,6 @@ const Polygons &DecomposedShape::transformed_outline() const
             poly.translate(translation());
         }
 
-        auto sc = scaled<double>(1.) * scaled<double>(1.);
         m_area = std::accumulate(m_transformed_outline.begin(),
                                  m_transformed_outline.end(), 0.,
                                  [sc](double s, const auto &p) {
@@ -88,6 +89,29 @@ const Vec2crd &DecomposedShape::min_vertex(size_t idx) const
     return m_mins[idx];
 }
 
+Vec2crd DecomposedShape::centroid() const
+{
+    constexpr double area_sc = scaled<double>(1.) * scaled(1.);
+
+    if (!m_centroid_valid) {
+        double total_area = 0.0;
+        Vec2d cntr = Vec2d::Zero();
+
+        for (const Polygon& poly : transformed_outline()) {
+            double parea = poly.area() / area_sc;
+            Vec2d pcntr = unscaled(poly.centroid());
+            total_area += parea;
+            cntr += pcntr * parea;
+        }
+
+        cntr /= total_area;
+        m_centroid = scaled(cntr);
+        m_centroid_valid = true;
+    }
+
+    return m_centroid;
+}
+
 DecomposedShape decompose(const ExPolygons &shape)
 {
     ExPolygons shape_s = expolygons_simplify(shape, scaled(.2));

src/libslic3r/Arrange/Items/ArrangeItem.hpp

@@ -55,6 +55,9 @@ class DecomposedShape
     mutable std::vector<Point> m_mins;
     mutable bool               m_reference_vertex_valid = false;
 
+    mutable Point m_centroid;
+    mutable bool  m_centroid_valid = false;
+
     mutable Polygon m_convex_hull;
     mutable BoundingBox m_bounding_box;
     mutable double  m_area = 0;
@@ -87,6 +90,7 @@ public:
         m_translation               = v;
         m_transformed_outline_valid = false;
         m_reference_vertex_valid    = false;
+        m_centroid_valid            = false;
     }
 
     void rotation(double v)
@@ -94,6 +98,7 @@ public:
         m_rotation                  = v;
         m_transformed_outline_valid = false;
         m_reference_vertex_valid    = false;
+        m_centroid_valid            = false;
     }
 
     const Polygons &transformed_outline() const;
@@ -115,6 +120,8 @@ public:
 
         return m_area;
     }
+
+    Vec2crd centroid() const;
 };
 
 DecomposedShape decompose(const ExPolygons &polys);
@@ -188,6 +195,8 @@ public:
     {
         m_shape.reference_vertex();
         m_envelope->reference_vertex();
+        m_shape.centroid();
+        m_envelope->centroid();
     }
 };
 
@@ -412,6 +421,16 @@ template<> struct NFPArrangeItemTraits_<ArrangeItem> {
 
         return *ret_ptr;
     }
+
+    static Vec2crd fixed_centroid(const ArrangeItem &itm)
+    {
+        return itm.shape().centroid();
+    }
+
+    static Vec2crd envelope_centroid(const ArrangeItem &itm)
+    {
+        return itm.envelope().centroid();
+    }
 };
 
 template<> struct IsWritableItem_<ArrangeItem>: public std::true_type {};

src/libslic3r/Arrange/Items/SimpleArrangeItem.hpp

@@ -138,6 +138,16 @@ template<> struct NFPArrangeItemTraits_<SimpleArrangeItem>
     {
         return itm.allowed_rotations();
     }
+
+    static Vec2crd fixed_centroid(const SimpleArrangeItem &itm) noexcept
+    {
+        return itm.shape().centroid();
+    }
+
+    static Vec2crd envelope_centroid(const SimpleArrangeItem &itm) noexcept
+    {
+        return itm.shape().centroid();
+    }
 };
 
 template<> struct IsWritableItem_<SimpleArrangeItem>: public std::true_type {};