Refactored Lightning infill to get rid of unnecessary std::list and std::unordered_map, which was slow.

src/libslic3r/Fill/Lightning/DistanceField.cpp

@@ -35,16 +35,18 @@ DistanceField::DistanceField(const coord_t& radius, const Polygons& current_outl
             assert(m_unsupported_points_bbox.contains(p));
         }
     }
-    m_unsupported_points.sort([&radius](const UnsupportedCell &a, const UnsupportedCell &b) {
+    std::stable_sort(m_unsupported_points.begin(), m_unsupported_points.end(), [&radius](const UnsupportedCell &a, const UnsupportedCell &b) {
         constexpr coord_t prime_for_hash = 191;
         return std::abs(b.dist_to_boundary - a.dist_to_boundary) > radius ?
                a.dist_to_boundary < b.dist_to_boundary :
                (PointHash{}(a.loc) % prime_for_hash) < (PointHash{}(b.loc) % prime_for_hash);
         });
-    for (auto it = m_unsupported_points.begin(); it != m_unsupported_points.end(); ++it) {
-        UnsupportedCell& cell = *it;
-        m_unsupported_points_grid.emplace(this->to_grid_point(cell.loc), it);
-    }
+
+    m_unsupported_points_erased.resize(m_unsupported_points.size());
+    std::fill(m_unsupported_points_erased.begin(), m_unsupported_points_erased.end(), false);
+
+    m_unsupported_points_grid.initialize(m_unsupported_points, [&self = std::as_const(*this)](const Point &p) -> Point { return self.to_grid_point(p); });
+
     // Because the distance between two points is at least one axis equal to m_cell_size, every cell
     // in m_unsupported_points_grid contains exactly one point.
     assert(m_unsupported_points.size() == m_unsupported_points_grid.size());
@@ -96,12 +98,11 @@ void DistanceField::update(const Point& to_node, const Point& added_leaf)
             }
             // Inside a circle at the end of the new leaf, or inside a rotated rectangle.
             // Remove unsupported leafs at this grid location.
-            if (auto it = m_unsupported_points_grid.find(grid_addr); it != m_unsupported_points_grid.end()) {
-                std::list<UnsupportedCell>::iterator& list_it = it->second;
-                UnsupportedCell& cell = *list_it;
+            if (const size_t cell_idx = m_unsupported_points_grid.find_cell_idx(grid_addr); cell_idx != std::numeric_limits<size_t>::max()) {
+                const UnsupportedCell &cell = m_unsupported_points[cell_idx];
                 if ((cell.loc - added_leaf).cast<int64_t>().squaredNorm() <= m_supporting_radius2) {
-                    m_unsupported_points.erase(list_it);
-                    m_unsupported_points_grid.erase(it);
+                    m_unsupported_points_erased[cell_idx] = true;
+                    m_unsupported_points_grid.mark_erased(grid_addr);
                 }
             }
         }

src/libslic3r/Fill/Lightning/DistanceField.hpp

@@ -38,12 +38,18 @@ public:
      * \return ``true`` if successful, or ``false`` if there are no more points
      * to consider.
      */
-    bool tryGetNextPoint(Point* p) const {
-        if (m_unsupported_points.empty())
-            return false;
-        *p = m_unsupported_points.front().loc;
+    bool tryGetNextPoint(Point *out_unsupported_location, size_t *out_unsupported_cell_idx, const size_t start_idx = 0) const
+    {
+        for (size_t point_idx = start_idx; point_idx < m_unsupported_points.size(); ++point_idx) {
+            if (!m_unsupported_points_erased[point_idx]) {
+                *out_unsupported_cell_idx = point_idx;
+                *out_unsupported_location = m_unsupported_points[point_idx].loc;
                 return true;
             }
+        }
+
+        return false;
+    }
 
     /*!
      * Update the distance field with a newly added branch.
@@ -87,7 +93,8 @@ protected:
     /*!
      * Cells which still need to be supported at some point.
      */
-    std::list<UnsupportedCell> m_unsupported_points;
+    std::vector<UnsupportedCell> m_unsupported_points;
+    std::vector<bool>            m_unsupported_points_erased;
 
     /*!
      * BoundingBox of all points in m_unsupported_points. Used for mapping of sign integer numbers to positive integer numbers.
@@ -98,7 +105,84 @@ protected:
      * Links the unsupported points to a grid point, so that we can quickly look
      * up the cell belonging to a certain position in the grid.
      */
-    std::unordered_map<Point, std::list<UnsupportedCell>::iterator, PointHash> m_unsupported_points_grid;
+
+    class UnsupportedPointsGrid
+    {
+    public:
+        UnsupportedPointsGrid() = default;
+        void initialize(const std::vector<UnsupportedCell> &unsupported_points, const std::function<Point(const Point &)> &map_cell_to_grid)
+        {
+            if (unsupported_points.empty())
+                return;
+
+            BoundingBox unsupported_points_bbox;
+            for (const UnsupportedCell &cell : unsupported_points)
+                unsupported_points_bbox.merge(cell.loc);
+
+            m_size        = unsupported_points.size();
+            m_grid_range  = BoundingBox(map_cell_to_grid(unsupported_points_bbox.min), map_cell_to_grid(unsupported_points_bbox.max));
+            m_grid_size   = m_grid_range.size() + Point::Ones();
+
+            m_data.assign(m_grid_size.y() * m_grid_size.x(), std::numeric_limits<size_t>::max());
+            m_data_erased.assign(m_grid_size.y() * m_grid_size.x(), true);
+
+            for (size_t cell_idx = 0; cell_idx < unsupported_points.size(); ++cell_idx) {
+                const size_t flat_idx   = map_to_flat_array(map_cell_to_grid(unsupported_points[cell_idx].loc));
+                assert(m_data[flat_idx] == std::numeric_limits<size_t>::max());
+                m_data[flat_idx]        = cell_idx;
+                m_data_erased[flat_idx] = false;
+            }
+        }
+
+        size_t size() const { return m_size; }
+
+        size_t find_cell_idx(const Point &grid_addr)
+        {
+            if (!m_grid_range.contains(grid_addr))
+                return std::numeric_limits<size_t>::max();
+
+            if (const size_t flat_idx = map_to_flat_array(grid_addr); !m_data_erased[flat_idx]) {
+                assert(m_data[flat_idx] != std::numeric_limits<size_t>::max());
+                return m_data[flat_idx];
+            }
+
+            return std::numeric_limits<size_t>::max();
+        }
+
+        void mark_erased(const Point &grid_addr)
+        {
+            assert(m_grid_range.contains(grid_addr));
+            if (!m_grid_range.contains(grid_addr))
+                return;
+
+            const size_t flat_idx = map_to_flat_array(grid_addr);
+            assert(!m_data_erased[flat_idx] && m_data[flat_idx] != std::numeric_limits<size_t>::max());
+            assert(m_size != 0);
+
+            m_data_erased[flat_idx] = true;
+            --m_size;
+        }
+
+    private:
+        size_t m_size = 0;
+
+        BoundingBox m_grid_range;
+        Point       m_grid_size;
+
+        std::vector<size_t> m_data;
+        std::vector<bool>   m_data_erased;
+
+        inline size_t map_to_flat_array(const Point &loc) const
+        {
+            const Point  offset_loc = loc - m_grid_range.min;
+            const size_t flat_idx   = m_grid_size.x() * offset_loc.y() + offset_loc.x();
+            assert(offset_loc.x() >= 0 && offset_loc.y() >= 0);
+            assert(flat_idx < m_grid_size.y() * m_grid_size.x());
+            return flat_idx;
+        }
+    };
+
+    UnsupportedPointsGrid m_unsupported_points_grid;
 
     /*!
      * Maps the point to the grid coordinates.

src/libslic3r/Fill/Lightning/Layer.cpp

@@ -56,8 +56,9 @@ void Layer::generateNewTrees
 
     // Until no more points need to be added to support all:
     // Determine next point from tree/outline areas via distance-field
+    size_t unsupported_cell_idx = 0;
     Point  unsupported_location;
-    while (distance_field.tryGetNextPoint(&unsupported_location)) {
+    while (distance_field.tryGetNextPoint(&unsupported_location, &unsupported_cell_idx, unsupported_cell_idx)) {
         throw_on_cancel_callback();
         GroundingLocation grounding_loc = getBestGroundingLocation(
             unsupported_location, current_outlines, current_outlines_bbox, outlines_locator, supporting_radius, wall_supporting_radius, tree_node_locator);