Clipper optimization:

1) Removed the already commented-out scaling / unscaling when doing
   "safe offsetting"
2) Removed some of the "safe offsetting" at calls where it never was used.
3) Reworked Clipper & ClipperUtils to pass Polygons / ExPolygons / Surfaces
   as input parameters without conversion to ClipperLib::Paths. This
   should save a lot of memory allocation and copying.
4) Reworked conversions from ClipperLib::Paths & PolyTree to Polygons /
   ExPolygons to use the move operator to avoid many unnecessary allocations.
5) Reworked some "union with safe ofsetting" to "offset_ex", which should
   be cheaper.

2 files changed, 15 insertions, 16 deletions

diff --git a/src/libslic3r/SLA/ConcaveHull.cpp b/src/libslic3r/SLA/ConcaveHull.cpp
index d3c0d1022..172408989 100644
--- a/src/libslic3r/SLA/ConcaveHull.cpp
+++ b/src/libslic3r/SLA/ConcaveHull.cpp
@@ -42,9 +42,10 @@ Point ConcaveHull::centroid(const Points &pp)
 
 // As it shows, the current offset_ex in ClipperUtils hangs if used in jtRound
 // mode
-static ClipperLib::Paths fast_offset(const ClipperLib::Paths &paths,
-                                     coord_t                  delta,
-                                     ClipperLib::JoinType     jointype)
+template<typename PolygonsProvider>
+static ClipperLib::Paths fast_offset(PolygonsProvider             &&paths,
+                                     coord_t                        delta,
+                                     ClipperLib::JoinType           jointype)
 {
     using ClipperLib::ClipperOffset;
     using ClipperLib::etClosedPolygon;
@@ -61,7 +62,7 @@ static ClipperLib::Paths fast_offset(const ClipperLib::Paths &paths,
             return {};
         }
 
-    offs.AddPaths(paths, jointype, etClosedPolygon);
+    offs.AddPaths(std::forward<PolygonsProvider>(paths), jointype, etClosedPolygon);
 
     Paths result;
     offs.Execute(result, static_cast<double>(delta));
@@ -157,11 +158,9 @@ ExPolygons ConcaveHull::to_expolygons() const
 
 ExPolygons offset_waffle_style_ex(const ConcaveHull &hull, coord_t delta)
 {
-    ClipperLib::Paths paths = Slic3rMultiPoints_to_ClipperPaths(hull.polygons());
-    paths = fast_offset(paths, 2 * delta, ClipperLib::jtRound);
-    paths = fast_offset(paths, -delta, ClipperLib::jtRound);
-    ExPolygons ret = ClipperPaths_to_Slic3rExPolygons(paths);
-    for (ExPolygon &p : ret) p.holes = {};
+    ExPolygons ret = ClipperPaths_to_Slic3rExPolygons(
+        fast_offset(fast_offset(ClipperUtils::PolygonsProvider(hull.polygons()), 2 * delta, ClipperLib::jtRound), -delta, ClipperLib::jtRound));
+    for (ExPolygon &p : ret) p.holes.clear();
     return ret;
 }
 
diff --git a/src/libslic3r/SLA/Pad.cpp b/src/libslic3r/SLA/Pad.cpp
index 927c32589..e11914a1c 100644
--- a/src/libslic3r/SLA/Pad.cpp
+++ b/src/libslic3r/SLA/Pad.cpp
@@ -179,10 +179,10 @@ PadSkeleton divide_blueprint(const ExPolygons &bp)
     ret.outer.reserve(size_t(ptree.Total()));
 
     for (ClipperLib::PolyTree::PolyNode *node : ptree.Childs) {
-        ExPolygon poly(ClipperPath_to_Slic3rPolygon(node->Contour));
+        ExPolygon poly;
+        poly.contour.points = std::move(node->Contour);
         for (ClipperLib::PolyTree::PolyNode *child : node->Childs) {
-            poly.holes.emplace_back(
-                ClipperPath_to_Slic3rPolygon(child->Contour));
+            poly.holes.emplace_back(std::move(child->Contour));
 
             traverse_pt(child->Childs, &ret.inner);
         }
@@ -342,18 +342,18 @@ public:
 template<class...Args>
 ExPolygon offset_contour_only(const ExPolygon &poly, coord_t delta, Args...args)
 {
-    ExPolygons tmp = offset_ex(poly.contour, float(delta), args...);
+    Polygons tmp = offset(poly.contour, float(delta), args...);
 
     if (tmp.empty()) return {};
 
     Polygons holes = poly.holes;
     for (auto &h : holes) h.reverse();
 
-    tmp = diff_ex(to_polygons(tmp), holes);
+    ExPolygons tmp2 = diff_ex(tmp, holes);
 
-    if (tmp.empty()) return {};
+    if (tmp2.empty()) return {};
 
-    return tmp.front();
+    return std::move(tmp2.front());
 }
 
 bool add_cavity(Contour3D &pad, ExPolygon &top_poly, const PadConfig3D &cfg,