WIP: Reworking of FillRectilinear2 to support monotonous infill

with ant colony optimization and 3-opt flips.

src/libslic3r/Fill/FillBase.hpp

@@ -5,6 +5,7 @@
 #include <memory.h>
 #include <float.h>
 #include <stdint.h>
+#include <stdexcept>
 
 #include <type_traits>
 
@@ -18,6 +19,11 @@ namespace Slic3r {
 class ExPolygon;
 class Surface;
 
+class InfillFailedException : public std::runtime_error {
+public:
+    InfillFailedException() : std::runtime_error("Infill failed") {}
+};
+
 struct FillParams
 {
     bool        full_infill() const { return density > 0.9999f; }