WIP Cura Lightning infill, initial port.

src/libslic3r/Fill/Lightning/DistanceField.hpp

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+//Copyright (c) 2021 Ultimaker B.V.
+//CuraEngine is released under the terms of the AGPLv3 or higher.
+
+#ifndef LIGHTNING_DISTANCE_FIELD_H
+#define LIGHTNING_DISTANCE_FIELD_H
+
+namespace Slic3r
+{
+
+/*!
+ * 2D field that maintains locations which need to be supported for Lightning
+ * Infill.
+ *
+ * This field contains a set of "cells", spaced out in a grid. Each cell
+ * maintains how far it is removed from the edge, which is used to determine
+ * how it gets supported by Lightning Infill.
+ */
+class LightningDistanceField
+{
+public:
+    /*!
+     * Construct a new field to calculate Lightning Infill with.
+     * \param radius The radius of influence that an infill line is expected to
+     * support in the layer above.
+     * \param current_outline The total infill area on this layer.
+     * \param current_overhang The overhang that needs to be supported on this
+     * layer.
+     */
+    LightningDistanceField(const coord_t& radius, const Polygons& current_outline, const Polygons& current_overhang);
+    
+    /*!
+     * Gets the next unsupported location to be supported by a new branch.
+     * \param p Output variable for the next point to support.
+     * \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;
+        return true;
+    }
+
+    /*!
+     * Update the distance field with a newly added branch.
+     *
+     * The branch is a line extending from \p to_node to \p added_leaf . This
+     * function updates the grid cells so that the distance field knows how far
+     * off it is from being supported by the current pattern. Grid points are
+     * updated with sampling points spaced out by the supporting radius along
+     * the line.
+     * \param to_node The node endpoint of the newly added branch.
+     * \param added_leaf The location of the leaf of the newly added branch,
+     * drawing a straight line to the node.
+     */
+    void update(const Point& to_node, const Point& added_leaf);
+
+protected:
+    /*!
+     * Spacing between grid points to consider supporting.
+     */
+    coord_t m_cell_size;
+
+    /*!
+     * The radius of the area of the layer above supported by a point on a
+     * branch of a tree.
+     */
+    coord_t m_supporting_radius;
+    double  m_supporting_radius2;
+
+    /*!
+     * Represents a small discrete area of infill that needs to be supported.
+     */
+    struct UnsupportedCell
+    {
+        UnsupportedCell(Point grid_loc, coord_t dist_to_boundary) : loc(loc), dist_to_boundary(dist_to_boundary) {}
+        // The position of the center of this cell.
+        Point loc;
+        // How far this cell is removed from the ``current_outline`` polygon, the edge of the infill area.
+        coord_t dist_to_boundary;
+    };
+
+    /*!
+     * Cells which still need to be supported at some point.
+     */
+    std::list<UnsupportedCell> m_unsupported_points;
+
+    /*!
+     * 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;
+};
+
+} // namespace Slic3r
+
+#endif //LIGHTNING_DISTANCE_FIELD_H