Refactoring of adaptive cubic infill:

Don't create an octree for the infill if it is not needed.

src/libslic3r/Fill/FillAdaptive.hpp

@@ -7,6 +7,8 @@
 
 namespace Slic3r {
 
+class PrintObject;
+
 namespace FillAdaptive_Internal
 {
     struct CubeProperties
@@ -82,6 +84,12 @@ public:
         int                             depth);
 };
 
+// Calculate line spacing for
+// 1) adaptive cubic infill
+// 2) adaptive internal support cubic infill
+// Returns zero for a particular infill type if no such infill is to be generated.
+std::pair<double, double> adaptive_fill_line_spacing(const PrintObject &print_object);
+
 } // namespace Slic3r
 
 #endif // slic3r_FillAdaptive_hpp_