Fills were reimplemented in C++.

While reimplementing the FillPlanePath code, the octagon infill was fixed to extrude the right amount of material.

xs/src/libslic3r/Fill/FillConcentric.cpp

@@ -0,0 +1,60 @@
+#include "../ClipperUtils.hpp"
+#include "../ExPolygon.hpp"
+#include "../Surface.hpp"
+
+#include "FillConcentric.hpp"
+
+namespace Slic3r {
+
+Polylines FillConcentric::fill_surface(const Surface *surface, const FillParams &params)
+{
+    // no rotation is supported for this infill pattern
+    ExPolygon expolygon = surface->expolygon;
+    BoundingBox bounding_box = expolygon.contour.bounding_box();
+    
+    coord_t min_spacing = scale_(this->spacing);
+    coord_t distance = coord_t(min_spacing / params.density);
+    
+    if (params.density > 0.9999f && !params.dont_adjust) {
+        distance = this->adjust_solid_spacing(bounding_box.size().x, distance);
+        this->spacing = unscale(distance);
+    }
+
+    Polygons loops = (Polygons)expolygon;
+    Polygons last  = loops;
+    while (! last.empty()) {
+        last = offset2(last, -(distance + min_spacing/2), +min_spacing/2);
+        loops.insert(loops.end(), last.begin(), last.end());
+    }
+
+    // generate paths from the outermost to the innermost, to avoid
+    // adhesion problems of the first central tiny loops
+    union_pt_chained(loops, &loops, false);
+    
+    // split paths using a nearest neighbor search
+    Polylines paths;
+    Point last_pos(0, 0);
+    for (Polygons::const_iterator it_loop = loops.begin(); it_loop != loops.end(); ++ it_loop) {
+        paths.push_back(it_loop->split_at_index(last_pos.nearest_point_index(*it_loop)));
+        last_pos = paths.back().last_point();
+    }
+
+    // clip the paths to prevent the extruder from getting exactly on the first point of the loop
+    // Keep valid paths only.
+    size_t j = 0;
+    for (size_t i = 0; i < paths.size(); ++ i) {
+        paths[i].clip_end(this->loop_clipping);
+        if (paths[i].is_valid()) {
+            if (j < i)
+                std::swap(paths[j], paths[i]);
+            ++ j;
+        }
+    }
+    if (j < paths.size())
+        paths.erase(paths.begin() + j, paths.end());
+
+    // TODO: return ExtrusionLoop objects to get better chained paths
+    return paths;
+}
+
+} // namespace Slic3r