WIP: Moved sources int src/, separated most of the source code from Perl.

The XS was left only for the unit / integration tests, and it links
libslic3r only. No wxWidgets are allowed to be used from Perl starting
from now.

src/libslic3r/Fill/FillHoneycomb.cpp

@@ -0,0 +1,125 @@
+#include "../ClipperUtils.hpp"
+#include "../PolylineCollection.hpp"
+#include "../Surface.hpp"
+
+#include "FillHoneycomb.hpp"
+
+namespace Slic3r {
+
+void FillHoneycomb::_fill_surface_single(
+    const FillParams                &params, 
+    unsigned int                     thickness_layers,
+    const std::pair<float, Point>   &direction, 
+    ExPolygon                       &expolygon, 
+    Polylines                       &polylines_out)
+{
+    // cache hexagons math
+    CacheID cache_id(params.density, this->spacing);
+    Cache::iterator it_m = this->cache.find(cache_id);
+    if (it_m == this->cache.end()) {
+        it_m = this->cache.insert(it_m, std::pair<CacheID, CacheData>(cache_id, CacheData()));
+        CacheData &m = it_m->second;
+        coord_t min_spacing = scale_(this->spacing);
+        m.distance = min_spacing / params.density;
+        m.hex_side = m.distance / (sqrt(3)/2);
+        m.hex_width = m.distance * 2; // $m->{hex_width} == $m->{hex_side} * sqrt(3);
+        coord_t hex_height = m.hex_side * 2;
+        m.pattern_height = hex_height + m.hex_side;
+        m.y_short = m.distance * sqrt(3)/3;
+        m.x_offset = min_spacing / 2;
+        m.y_offset = m.x_offset * sqrt(3)/3;
+        m.hex_center = Point(m.hex_width/2, m.hex_side);
+    }
+    CacheData &m = it_m->second;
+
+    Polygons polygons;
+    {
+        // adjust actual bounding box to the nearest multiple of our hex pattern
+        // and align it so that it matches across layers
+        
+        BoundingBox bounding_box = expolygon.contour.bounding_box();
+        {
+            // rotate bounding box according to infill direction
+            Polygon bb_polygon = bounding_box.polygon();
+            bb_polygon.rotate(direction.first, m.hex_center);
+            bounding_box = bb_polygon.bounding_box();
+            
+            // extend bounding box so that our pattern will be aligned with other layers
+            // $bounding_box->[X1] and [Y1] represent the displacement between new bounding box offset and old one
+            // The infill is not aligned to the object bounding box, but to a world coordinate system. Supposedly good enough.
+            bounding_box.merge(_align_to_grid(bounding_box.min, Point(m.hex_width, m.pattern_height)));
+        }
+
+        coord_t x = bounding_box.min(0);
+        while (x <= bounding_box.max(0)) {
+            Polygon p;
+            coord_t ax[2] = { x + m.x_offset, x + m.distance - m.x_offset };
+            for (size_t i = 0; i < 2; ++ i) {
+                std::reverse(p.points.begin(), p.points.end()); // turn first half upside down
+                for (coord_t y = bounding_box.min(1); y <= bounding_box.max(1); y += m.y_short + m.hex_side + m.y_short + m.hex_side) {
+                    p.points.push_back(Point(ax[1], y + m.y_offset));
+                    p.points.push_back(Point(ax[0], y + m.y_short - m.y_offset));
+                    p.points.push_back(Point(ax[0], y + m.y_short + m.hex_side + m.y_offset));
+                    p.points.push_back(Point(ax[1], y + m.y_short + m.hex_side + m.y_short - m.y_offset));
+                    p.points.push_back(Point(ax[1], y + m.y_short + m.hex_side + m.y_short + m.hex_side + m.y_offset));
+                }
+                ax[0] = ax[0] + m.distance;
+                ax[1] = ax[1] + m.distance;
+                std::swap(ax[0], ax[1]); // draw symmetrical pattern
+                x += m.distance;
+            }
+            p.rotate(-direction.first, m.hex_center);
+            polygons.push_back(p);
+        }
+    }
+    
+    if (params.complete || true) {
+        // we were requested to complete each loop;
+        // in this case we don't try to make more continuous paths
+        Polygons polygons_trimmed = intersection((Polygons)expolygon, polygons);
+        for (Polygons::iterator it = polygons_trimmed.begin(); it != polygons_trimmed.end(); ++ it)
+            polylines_out.push_back(it->split_at_first_point());
+    } else {
+        // consider polygons as polylines without re-appending the initial point:
+        // this cuts the last segment on purpose, so that the jump to the next 
+        // path is more straight
+        Polylines paths;
+        {
+            Polylines p;
+            for (Polygon &poly : polygons)
+                p.emplace_back(poly.points);
+            paths = intersection_pl(p, to_polygons(expolygon));
+        }
+
+        // connect paths
+        if (! paths.empty()) { // prevent calling leftmost_point() on empty collections
+            Polylines chained = PolylineCollection::chained_path_from(
+                std::move(paths), 
+                PolylineCollection::leftmost_point(paths), false);
+            assert(paths.empty());
+            paths.clear();
+            for (Polylines::iterator it_path = chained.begin(); it_path != chained.end(); ++ it_path) {
+                if (! paths.empty()) {
+                    // distance between first point of this path and last point of last path
+                    double distance = (it_path->first_point() - paths.back().last_point()).cast<double>().norm();
+                    if (distance <= m.hex_width) {
+                        paths.back().points.insert(paths.back().points.end(), it_path->points.begin(), it_path->points.end());
+                        continue;
+                    }
+                }
+                // Don't connect the paths.
+                paths.push_back(*it_path);
+            }
+        }
+        
+        // clip paths again to prevent connection segments from crossing the expolygon boundaries
+        paths = intersection_pl(paths, to_polygons(offset_ex(expolygon, SCALED_EPSILON)));
+        // Move the polylines to the output, avoid a deep copy.
+        size_t j = polylines_out.size();
+        polylines_out.resize(j + paths.size(), Polyline());
+        for (size_t i = 0; i < paths.size(); ++ i)
+            std::swap(polylines_out[j ++], paths[i]);
+    }
+}
+
+} // namespace Slic3r