ENH: use spiral lift only when it is needed

If a travel path goes through an overhang expolygons, and their distance
is shorter than threshold, lift type will be set to SpiralLift.

Signed-off-by: yifan.wu <yifan.wu@bambulab.com>
Change-Id: I345788711755dd8611ecf385818e6052cd8abe9e

src/libslic3r/Print.hpp

@@ -84,7 +84,10 @@ enum PrintStep {
 
 enum PrintObjectStep {
     posSlice, posPerimeters, posPrepareInfill,
-    posInfill, posIroning, posSupportMaterial, posSimplifyPath, posSimplifySupportPath, posCount,
+    posInfill, posIroning, posSupportMaterial, posSimplifyPath, posSimplifySupportPath,
+    // BBS
+    posDetectOverhangsForLift,
+    posCount,
 };
 
 // A PrintRegion object represents a group of volumes to print
@@ -445,6 +448,10 @@ private:
     void slice_volumes();
     //BBS
     ExPolygons _shrink_contour_holes(double contour_delta, double hole_delta, const ExPolygons& polys) const;
+    // BBS
+    void detect_overhangs_for_lift();
+    void clear_overhangs_for_lift();
+
     // Has any support (not counting the raft).
     void detect_surfaces_type();
     void process_external_surfaces();