FIX: fix two tree support bugs

1. hybrid(auto) on_buildplate_only option not working correctly because
parent is not set.
2. tree(auto) on_buildplate_only not working correctly because unsupported
branch isn't deleted completely. I add child to track the dangling nodes
and then delete nodes with no child.

Change-Id: I24c69a7cf400d2961b22a720a6069cf95db6c1a5
(cherry picked from commit bce77c16128d35c668b175e7135b9fe9acd71d13)

src/libnest2d/include/libnest2d/selections/firstfit.hpp

@@ -2,6 +2,8 @@
 #define FIRSTFIT_HPP
 
 #include "selection_boilerplate.hpp"
+// for writing SVG
+//#include "../tools/svgtools.hpp"
 
 namespace libnest2d { namespace selections {
 
@@ -60,14 +62,11 @@ public:
             pconfig.m_excluded_items.emplace_back(itm);
             });
 
-        // If the packed_items array is not empty we have to create as many
-        // placers as there are elements in packed bins and preload each item
-        // into the appropriate placer
-        //for(ItemGroup& ig : fixed_bins) {
-        //    placers.emplace_back(bin);
-        //    placers.back().configure(pconfig);
-        //    placers.back().preload(ig);
-        //}
+#ifdef SVGTOOLS_HPP
+        svg::SVGWriter<RawShape> svgwriter;
+        std::for_each(first, last, [this,&svgwriter](Item &itm) { svgwriter.writeShape(itm, "none", "blue"); });
+        svgwriter.save(boost::filesystem::path("SVG") / "all_items.svg");
+#endif
         
         std::function<bool(Item& i1, Item& i2)> sortfunc;
         if (pconfig.sortfunc)

src/libslic3r/TreeSupport.cpp

@@ -2271,11 +2271,9 @@ void TreeSupport::drop_nodes(std::vector<std::vector<Node*>>& contact_nodes)
         for (Node* p_node : layer_contact_nodes)
         {
             if (p_node->type == ePolygon) {
-                Node* next_node = new Node(*p_node);
-                next_node->distance_to_top++;
-                next_node->support_roof_layers_below--;
-                next_node->print_z -= m_object->get_layer(layer_nr)->height;
-                next_node->to_buildplate = !is_inside_ex(m_ts_data->m_layer_outlines[layer_nr], next_node->position);
+                 const bool to_buildplate = !is_inside_ex(m_ts_data->m_layer_outlines[layer_nr], p_node->position);
+                 Node *     next_node     = new Node(p_node->position, p_node->distance_to_top + 1, p_node->skin_direction, p_node->support_roof_layers_below - 1, to_buildplate, p_node,
+                                            m_object->get_layer(layer_nr - 1)->print_z, m_object->get_layer(layer_nr - 1)->height);
                 contact_nodes[layer_nr - 1].emplace_back(next_node);
             }
         }
@@ -2607,6 +2605,20 @@ void TreeSupport::drop_nodes(std::vector<std::vector<Node*>>& contact_nodes)
         }
     }
 
+    // delete nodes with no children (means either it's a single layer nodes, or the branch has been deleted but not completely)
+    for (size_t layer_nr = contact_nodes.size() - 1; layer_nr > 0; layer_nr--){
+        auto layer_contact_nodes = contact_nodes[layer_nr];
+        for (Node *p_node : layer_contact_nodes) {
+            if (p_node->child==nullptr) {
+                std::vector<Node *>::iterator to_erase = std::find(contact_nodes[layer_nr].begin(), contact_nodes[layer_nr].end(), p_node);
+                if (to_erase != contact_nodes[layer_nr].end()) {
+                    to_free_node_set.insert(*to_erase);
+                    contact_nodes[layer_nr].erase(to_erase);
+                }
+            }
+        }
+    }
+
     BOOST_LOG_TRIVIAL(debug) << "after m_avoidance_cache.size()=" << m_ts_data->m_avoidance_cache.size();
 
     for (Node *node : to_free_node_set)

src/libslic3r/TreeSupport.hpp

@@ -222,7 +222,7 @@ public:
          , height(0.0)
         {}
 
-        Node(const Point position, const size_t distance_to_top, const bool skin_direction, const int support_roof_layers_below, const bool to_buildplate, Node* const parent,
+        Node(const Point position, const size_t distance_to_top, const bool skin_direction, const int support_roof_layers_below, const bool to_buildplate, Node* parent,
              coordf_t     print_z_, coordf_t height_)
          : distance_to_top(distance_to_top)
          , position(position)
@@ -233,7 +233,13 @@ public:
          , parent(parent)
          , print_z(print_z_)
          , height(height_)
-        {}
+        {
+            if (parent) {
+                type     = parent->type;
+                overhang = parent->overhang;
+                parent->child = this;
+            }
+        }
 
 #ifdef DEBUG // Clear the delete node's data so if there's invalid access after, we may get a clue by inspecting that node.
         ~Node()
@@ -294,6 +300,7 @@ public:
          * the entire branch needs to be known.
          */
         Node *parent;
+        Node *child = nullptr;
 
         /*!
         * \brief All neighbours (on the same layer) that where merged into this node.