ENH: add arachne engine for narrow internal solid infill

ConcentricGapFill pattern was used for internal narrow
solid infill. Use arachne engine instead to remove
gap fill inside the pattern and improve the extrusion path

Signed-off-by: salt.wei <salt.wei@bambulab.com>
Change-Id: I758d7c72eb71cc37026b7cebf746cc345014c3f5
(cherry picked from commit 0b6bacd21a091afc13d7b36a69e5b10f155bc6f8)

src/libslic3r/Arachne/SkeletalTrapezoidationGraph.hpp

@@ -0,0 +1,105 @@
+//Copyright (c) 2020 Ultimaker B.V.
+//CuraEngine is released under the terms of the AGPLv3 or higher.
+
+#ifndef SKELETAL_TRAPEZOIDATION_GRAPH_H
+#define SKELETAL_TRAPEZOIDATION_GRAPH_H
+
+#include <optional>
+
+#include "utils/HalfEdgeGraph.hpp"
+#include "SkeletalTrapezoidationEdge.hpp"
+#include "SkeletalTrapezoidationJoint.hpp"
+
+namespace Slic3r::Arachne
+{
+
+class STHalfEdgeNode;
+
+class STHalfEdge : public HalfEdge<SkeletalTrapezoidationJoint, SkeletalTrapezoidationEdge, STHalfEdgeNode, STHalfEdge>
+{
+    using edge_t = STHalfEdge;
+    using node_t = STHalfEdgeNode;
+public:
+    STHalfEdge(SkeletalTrapezoidationEdge data);
+
+    /*!
+        * Check (recursively) whether there is any upward edge from the distance_to_boundary of the from of the \param edge
+        *
+        * \param strict Whether equidistant edges can count as a local maximum
+        */
+    bool canGoUp(bool strict = false) const;
+
+    /*!
+        * Check whether the edge goes from a lower to a higher distance_to_boundary.
+        * Effectively deals with equidistant edges by looking beyond this edge.
+        */
+    bool isUpward() const;
+
+    /*!
+        * Calculate the traversed distance until we meet an upward edge.
+        * Useful for calling on edges between equidistant points.
+        *
+        * If we can go up then the distance includes the length of the \param edge
+        */
+    std::optional<coord_t> distToGoUp() const;
+
+    STHalfEdge* getNextUnconnected();
+};
+
+class STHalfEdgeNode : public HalfEdgeNode<SkeletalTrapezoidationJoint, SkeletalTrapezoidationEdge, STHalfEdgeNode, STHalfEdge>
+{
+    using edge_t = STHalfEdge;
+    using node_t = STHalfEdgeNode;
+public:
+    STHalfEdgeNode(SkeletalTrapezoidationJoint data, Point p);
+
+    bool isMultiIntersection();
+
+    bool isCentral() const;
+
+    /*!
+        * Check whether this node has a locally maximal distance_to_boundary
+        *
+        * \param strict Whether equidistant edges can count as a local maximum
+        */
+    bool isLocalMaximum(bool strict = false) const;
+};
+
+class SkeletalTrapezoidationGraph: public HalfEdgeGraph<SkeletalTrapezoidationJoint, SkeletalTrapezoidationEdge, STHalfEdgeNode, STHalfEdge>
+{
+    using edge_t = STHalfEdge;
+    using node_t = STHalfEdgeNode;
+public:
+
+    /*!
+     * If an edge is too small, collapse it and its twin and fix the surrounding edges to ensure a consistent graph.
+     * 
+     * Don't collapse support edges, unless we can collapse the whole quad.
+     * 
+     * o-,
+     * |  "-o
+     * |    | > Don't collapse this edge only.
+     * o    o
+     */
+    void collapseSmallEdges(coord_t snap_dist = 5);
+
+    void makeRib(edge_t*& prev_edge, Point start_source_point, Point end_source_point, bool is_next_to_start_or_end);
+
+    /*!
+     * Insert a node into the graph and connect it to the input polygon using ribs
+     * 
+     * \return the last edge which replaced [edge], which points to the same [to] node
+     */
+    edge_t* insertNode(edge_t* edge, Point mid, coord_t mide_node_bead_count);
+
+    /*!
+     * Return the first and last edge of the edges replacing \p edge pointing to the same node
+     */
+    std::pair<edge_t*, edge_t*> insertRib(edge_t& edge, node_t* mid_node);
+
+protected:
+    Line getSource(const edge_t& edge) const;
+};
+
+}
+#endif