Cut: contours indexing no longer breaks when the normal is inverted,

detection of the situation when all parts are assigned to one side

src/slic3r/GUI/Gizmos/GLGizmoCut.cpp

@@ -1563,6 +1563,21 @@ void GLGizmoCut3D::PartSelection::render(const Vec3d* normal, GLModel& sphere_mo
 }
 
 
+bool GLGizmoCut3D::PartSelection::is_one_object() const
+{
+    // In theory, the implementation could be just this:
+    // return m_contour_to_parts.size() == m_ignored_contours.size();
+    // However, this would require that the part-contour correspondence works
+    // flawlessly. Because it is currently not always so for self-intersecting
+    // objects, let's better check the parts itself:
+    if (m_parts.size() < 2)
+        return true;
+    return std::all_of(m_parts.begin(), m_parts.end(), [this](const Part& part) {
+        return part.selected == m_parts.front().selected;
+    });
+}
+
+
 void GLGizmoCut3D::PartSelection::toggle_selection(const Vec2d& mouse_pos)
 {
     // FIXME: Cache the transforms.
@@ -1984,7 +1999,7 @@ void GLGizmoCut3D::render_cut_plane_input_window(CutConnectors &connectors)
 
         add_vertical_scaled_interval(0.75f);
 
-        m_imgui->disabled_begin(!m_keep_upper || !m_keep_lower || m_keep_as_parts);
+        m_imgui->disabled_begin(!m_keep_upper || !m_keep_lower || m_keep_as_parts || (m_part_selection.valid() && m_part_selection.is_one_object()));
             if (m_imgui->button(has_connectors ? _L("Edit connectors") : _L("Add connectors")))
                 set_connectors_editing(true);
         m_imgui->disabled_end();
@@ -2404,6 +2419,8 @@ bool GLGizmoCut3D::can_perform_cut() const
 {
     if (! m_invalid_connectors_idxs.empty() || (!m_keep_upper && !m_keep_lower) || m_connectors_editing)
         return false;
+    if (m_part_selection.valid())
+        return ! m_part_selection.is_one_object();
 
     return true;// has_valid_contour();
 }

src/slic3r/GUI/Gizmos/GLGizmoCut.hpp

@@ -155,20 +155,20 @@ class GLGizmoCut3D : public GLGizmoBase
         void turn_over_selection();
         ModelObject* model_object() { return m_model.objects.front(); }
         bool valid() const { return m_valid; }
+        bool is_one_object() const;
         const std::vector<Part>& parts() const { return m_parts; }
         const std::vector<size_t>* get_ignored_contours_ptr() const { return (valid() ? &m_ignored_contours : nullptr); }
 
-        std::vector<Vec3d> m_contour_points; // TEMPORARILY PUBLIC
-        std::vector<std::pair<std::vector<size_t>, std::vector<size_t>>> m_contour_to_parts; // for each contour, there is a vector of parts above and a vector of parts below
-        std::vector<size_t> m_ignored_contours; // contour that should not be rendered (the parts on both sides will both be parts of the same object)
-        std::vector<std::vector<Vec3d>> m_debug_pts;
-
-
     private:
         Model m_model;
         int m_instance_idx;
         std::vector<Part> m_parts;
         bool m_valid = false;
+        std::vector<std::pair<std::vector<size_t>, std::vector<size_t>>> m_contour_to_parts; // for each contour, there is a vector of parts above and a vector of parts below
+        std::vector<size_t> m_ignored_contours; // contour that should not be rendered (the parts on both sides will both be parts of the same object)
+
+        std::vector<Vec3d> m_contour_points;         // Debugging
+        std::vector<std::vector<Vec3d>> m_debug_pts; // Debugging
     };
 
     PartSelection m_part_selection;

src/slic3r/GUI/MeshUtils.cpp

@@ -174,13 +174,40 @@ bool MeshClipper::has_valid_contour() const
 
 std::vector<Vec3d> MeshClipper::point_per_contour() const
 {
+    assert(m_result);
     std::vector<Vec3d> out;
-    if (!m_result || m_result->cut_islands.empty())
-        return out;
     
     for (const CutIsland& isl : m_result->cut_islands) {
-        // FIXME: There might be holes !
+        assert(isl.expoly.contour.size() > 2);
-        Vec2d c = unscale(isl.expoly.contour.centroid());
+        // Now return a point lying inside the contour but not in a hole.
+        // We do this by taking a point lying close to the edge, repeating
+        // this several times for different edges and distances from them.
+        // (We prefer point not extremely close to the border.
+        bool done = false;
+        Vec2d p;
+        size_t i = 1;
+        while (i < isl.expoly.contour.size()) {
+            const Vec2d& a = unscale(isl.expoly.contour.points[i-1]);
+            const Vec2d& b = unscale(isl.expoly.contour.points[i]);
+            Vec2d n = (b-a).normalized();
+            std::swap(n.x(), n.y());
+            n.x() = -1 * n.x();
+            double f = 10.;
+            while (f > 0.05) {
+                p = (0.5*(b+a)) + f * n;
+                if (isl.expoly.contains(Point::new_scale(p))) {
+                    done = true;
+                    break;
+                }
+                f = f/10.;
+            }
+            if (done)
+                break;
+            i += isl.expoly.contour.size() / 5;
+        }
+        // If the above failed, just return the centroid, regardless of whether
+        // it is inside the contour or in a hole (we must return something).
+        Vec2d c = done ? p : unscale(isl.expoly.contour.centroid());
         out.emplace_back(m_result->trafo * Vec3d(c.x(), c.y(), 0.));
     }
     return out;
@@ -366,9 +393,20 @@ void MeshClipper::recalculate_triangles()
 
         isl.expoly = std::move(exp);
         isl.expoly_bb = get_extents(exp);
+        isl.hash = 0;
+        for (const Point& pt : isl.expoly.contour) {
+            isl.hash ^= pt.x();
+            isl.hash ^= pt.y();
         }
     }
 
+    // Now sort the islands so they are in defined order. This is a hack needed by cut gizmo, which sometimes
+    // flips the normal of the cut, in which case the contours stay the same but their order may change.
+    std::sort(m_result->cut_islands.begin(), m_result->cut_islands.end(), [](const CutIsland& a, const CutIsland& b) {
+        return a.hash < b.hash;
+    });
+}
+
 
 Vec3f MeshRaycaster::get_triangle_normal(size_t facet_idx) const
 {

src/slic3r/GUI/MeshUtils.hpp

@@ -141,6 +141,7 @@ private:
         ExPolygon expoly;
         BoundingBox expoly_bb;
         bool disabled = false;
+        coord_t hash;
     };
     struct ClipResult {
         std::vector<CutIsland> cut_islands;