Fixing zero elevation bug when concave hull overlap was not detected.

Backported from tm_perf_optims

src/libslic3r/MTUtils.hpp

@@ -320,6 +320,9 @@ using FloatingOnly = enable_if_t<std::is_floating_point<T>::value, O>;
 template<class T, class O = T>
 using ScaledCoordOnly = enable_if_t<is_scaled_coord<T>::value, O>;
 
+template<class T, class O = T>
+using IntegerOnly = enable_if_t<std::is_integral<T>::value, O>;
+
 template<class T, class O = T>
 using ArithmeticOnly = enable_if_t<std::is_arithmetic<T>::value, O>;
 
@@ -384,6 +387,13 @@ unscaled(const Eigen::Matrix<Tin, N, EigenArgs...> &v) noexcept
     return v.template cast<Tout>() * SCALING_FACTOR;
 }
 
+template<class T> inline std::vector<T> reserve_vector(size_t capacity)
+{
+    std::vector<T> ret;
+    ret.reserve(capacity);
+    return ret;
+}
+
 } // namespace Slic3r
 
 #endif // MTUTILS_HPP

src/libslic3r/SLA/SLABasePool.cpp

@@ -591,8 +591,7 @@ inline Point centroid(const Polygon& poly) {
 /// with explicit bridges. Bridges are generated from each shape's centroid
 /// to the center of the "scene" which is the centroid calculated from the shape
 /// centroids (a star is created...)
-Polygons concave_hull(const Polygons& polys, double max_dist_mm = 50,
-                      ThrowOnCancel throw_on_cancel = [](){})
+Polygons concave_hull(const Polygons& polys, double maxd_mm, ThrowOnCancel thr)
 {
     namespace bgi = boost::geometry::index;
     using SpatElement = std::pair<Point, unsigned>;
@@ -600,7 +599,7 @@ Polygons concave_hull(const Polygons& polys, double max_dist_mm = 50,
 
     if(polys.empty()) return Polygons();
     
-    const double max_dist = scaled(max_dist_mm);
+    const double max_dist = scaled(maxd_mm);
 
     Polygons punion = unify(polys);   // could be redundant
 
@@ -624,10 +623,10 @@ Polygons concave_hull(const Polygons& polys, double max_dist_mm = 50,
     idx = 0;
     std::transform(centroids.begin(), centroids.end(),
                    std::back_inserter(punion),
-                   [&centroids, &ctrindex, cc, max_dist, &idx, throw_on_cancel]
+                   [&centroids, &ctrindex, cc, max_dist, &idx, thr]
                    (const Point& c)
     {
-        throw_on_cancel();
+        thr();
         double dx = x(c) - x(cc), dy = y(c) - y(cc);
         double l = std::sqrt(dx * dx + dy * dy);
         double nx = dx / l, ny = dy / l;

src/libslic3r/SLA/SLABasePool.hpp

@@ -41,6 +41,9 @@ void breakstick_holes(ExPolygon &poly,
                       double     stick_width,
                       double     penetration = 0.0);
 
+Polygons concave_hull(const Polygons& polys, double max_dist_mm = 50,
+                      ThrowOnCancel throw_on_cancel = [](){});
+
 struct PoolConfig {
     double min_wall_thickness_mm = 2;
     double min_wall_height_mm = 5;

src/libslic3r/SLA/SLASupportTree.cpp

@@ -618,15 +618,25 @@ struct Pad {
                 }
             }
             
+            ExPolygons concaveh = offset_ex(
+                concave_hull(basep, pcfg.max_merge_distance_mm, thr),
+                scaled<float>(pcfg.min_wall_thickness_mm));
+            
             // Punching the breaksticks across the offsetted polygon perimeters
-            ExPolygons pad_stickholes; pad_stickholes.reserve(modelbase.size());
+            auto pad_stickholes = reserve_vector<ExPolygon>(modelbase.size());
             for(auto& poly : modelbase_offs) {
                 
+                bool overlap = false;
+                for (const ExPolygon &p : concaveh)
+                    overlap = overlap || poly.overlaps(p);
+                
+                auto bb = poly.contour.bounding_box();
+                bb.offset(scaled<float>(pcfg.min_wall_thickness_mm));
+                
                 std::vector<BoxIndexEl> qres =
-                    bindex.query(poly.contour.bounding_box(),
-                                 BoxIndex::qtIntersects);
-                    
-                if (!qres.empty()) {
+                    bindex.query(bb, BoxIndex::qtIntersects);
+                
+                if (!qres.empty() || overlap) {
                     
                     // The model silhouette polygon 'poly' HAS an intersection
                     // with the support silhouettes. Include this polygon