ENH: improve sharp detection for small regions

1. improve sharp detection for small regions.
   When the region is around 1 extrsion width, previous method may miss some sharp tails.
Now we reduce the width threshold to 0.1*extrusion_width for sharp
tails.
   When checking "nothing below", need to expand the poly a little. Example:
benchy.
2. improve is_support_necessary.
   Only popup warning for sharp tail and large cantilever (longer than 6mm).

Jira: STUDIO-2567
Change-Id: I5e977e7766b35409891d1b41e36278e3f07fa372
(cherry picked from commit c9d8a7c1c3bbd4367c7fc44408c67e5c534167f4)

src/libslic3r/Print.hpp

@@ -51,6 +51,7 @@ struct groupedVolumeSlices
 enum SupportNecessaryType {
     NoNeedSupp=0,
     SharpTail,
+    Cantilever,
     LargeOverhang,
 };
 

src/libslic3r/PrintObject.cpp

@@ -458,7 +458,7 @@ void PrintObject::generate_support_material()
 
             this->_generate_support_material();
             m_print->throw_if_canceled();
-        } else {
+        } else if(!m_print->get_no_check_flag()) {
             // BBS: pop a warning if objects have significant amount of overhangs but support material is not enabled
             m_print->set_status(50, L("Checking support necessity"));
             typedef std::chrono::high_resolution_clock clock_;
@@ -468,20 +468,16 @@ void PrintObject::generate_support_material()
             SupportNecessaryType sntype = this->is_support_necessary();
 
             double duration{ std::chrono::duration_cast<second_>(clock_::now() - t0).count() };
-            BOOST_LOG_TRIVIAL(info) << std::fixed << std::setprecision(0)
+            BOOST_LOG_TRIVIAL(info) << std::fixed << std::setprecision(0) << "is_support_necessary takes " << duration << " secs.";
-                << "is_support_necessary took " << (duration / 60) << " minutes and "
-                << std::setprecision(3)
-                << std::fmod(duration, 60.0) << " seconds." << std::endl;
 
             if (sntype != NoNeedSupp) {
-                if (sntype == SharpTail) {
+                std::map<SupportNecessaryType, std::string> reasons = {
-                    std::string warning_message = format(L("It seems object %s has completely floating regions. Please re-orient the object or enable support generation."),
+                    {SharpTail,L("floating regions")},
-                                                         this->model_object()->name);
+                    {Cantilever,L("floating cantilever")},
+                    {LargeOverhang,L("large overhangs")} };
+                std::string warning_message = format(L("It seems object %s has %s. Please re-orient the object or enable support generation."),
+                    this->model_object()->name, reasons[sntype]);
                 this->active_step_add_warning(PrintStateBase::WarningLevel::CRITICAL, warning_message, PrintStateBase::SlicingNeedSupportOn);
-                } else {
-                    std::string warning_message = format(L("It seems object %s has large overhangs. Please enable support generation."), this->model_object()->name);
-                    this->active_step_add_warning(PrintStateBase::WarningLevel::CRITICAL, warning_message, PrintStateBase::SlicingNeedSupportOn);
-                }
             }
 
 #if 0
@@ -2580,9 +2576,9 @@ template void PrintObject::remove_bridges_from_contacts<Polygons>(
 
 SupportNecessaryType PrintObject::is_support_necessary()
 {
-#if 0
     static const double super_overhang_area_threshold = SQ(scale_(5.0));
-
+    const double cantilevel_dist_thresh = scale_(6);
+#if 0
     double threshold_rad = (m_config.support_threshold_angle.value < EPSILON ? 30 : m_config.support_threshold_angle.value + 1) * M_PI / 180.;
     int enforce_support_layers = m_config.enforce_support_layers;
     const coordf_t extrusion_width = m_config.line_width.value;
@@ -2670,8 +2666,8 @@ SupportNecessaryType PrintObject::is_support_necessary()
     this->clear_support_layers();
     if (tree_support.has_sharp_tails)
         return SharpTail;
-    else if (tree_support.has_cantilever)
+    else if (tree_support.has_cantilever && tree_support.max_cantilevel_dist > cantilevel_dist_thresh)
-        return LargeOverhang;
+        return Cantilever;
 #endif
     return NoNeedSupp;
 }

src/libslic3r/SupportMaterial.cpp

@@ -1638,8 +1638,8 @@ static inline ExPolygons detect_overhangs(
                     // 1. nothing below
                     // Check whether this is a sharp tail region.
                     // Should use lower_layer_expolys without any offset. Otherwise, it may missing sharp tails near the main body.
-                    if (g_config_support_sharp_tails && overlaps({ expoly }, lower_layer_expolys)) {
+                    if (g_config_support_sharp_tails && overlaps(offset_ex(expoly, 0.5 * fw), lower_layer_expolys)) {
-                        is_sharp_tail = expoly.area() < area_thresh_well_supported && !offset_ex(expoly,-0.5*fw).empty();
+                        is_sharp_tail = expoly.area() < area_thresh_well_supported && !offset_ex(expoly,-0.1*fw).empty();
                     }
 
                     if (is_sharp_tail) {
@@ -2366,6 +2366,7 @@ PrintObjectSupportMaterial::MyLayersPtr PrintObjectSupportMaterial::top_contact_
             if (layer->lower_layer == NULL) continue;
             Layer* lower_layer = layer->lower_layer;
             auto cluster_boundary = intersection(cluster.merged_overhangs_dilated, offset(lower_layer->lslices, scale_(0.5)));
+            if (cluster_boundary.empty()) continue;
             double dist_max = 0;
             Points cluster_pts;
             for (auto& poly : cluster.merged_overhangs_dilated)

src/libslic3r/TreeSupport.cpp

@@ -898,8 +898,8 @@ void TreeSupport::detect_overhangs(bool detect_first_sharp_tail_only)
                         bool  is_sharp_tail = false;
                         // 1. nothing below
                         // this is a sharp tail region if it's small but non-ignorable
-                        if (!overlaps({ expoly }, lower_polys)) {
+                        if (!overlaps(offset_ex(expoly, 0.5 * extrusion_width_scaled), lower_polys)) {
-                            is_sharp_tail = expoly.area() < area_thresh_well_supported && !offset_ex(expoly, -0.5 * extrusion_width_scaled).empty();
+                            is_sharp_tail = expoly.area() < area_thresh_well_supported && !offset_ex(expoly, -0.1 * extrusion_width_scaled).empty();
                         }
 
                         if (is_sharp_tail) {
@@ -912,7 +912,10 @@ void TreeSupport::detect_overhangs(bool detect_first_sharp_tail_only)
                                 has_sharp_tails = true;
 #ifdef SUPPORT_TREE_DEBUG_TO_SVG
                             SVG svg(get_svg_filename(std::to_string(layer->print_z), "sharp_tail"), m_object->bounding_box());
-                            if (svg.is_opened()) svg.draw(overhang, "yellow");
+                            if (svg.is_opened()) {
+                                svg.draw(overhang, "yellow");
+                                svg.draw(lower_layer->lslices, "red");
+                            }
 #endif
                         }
                     }
@@ -1045,11 +1048,13 @@ void TreeSupport::detect_overhangs(bool detect_first_sharp_tail_only)
     m_object->project_and_append_custom_facets(false, EnforcerBlockerType::BLOCKER, blockers);
 
     // check whether the overhang cluster is cantilever (far awary from main body)
+    max_cantilevel_dist = 0;
     for (auto& cluster : overhangClusters) {
         Layer* layer = m_object->get_layer(cluster.min_layer);
         if (layer->lower_layer == NULL) continue;
         Layer* lower_layer = layer->lower_layer;
         auto cluster_boundary = intersection(cluster.merged_poly, offset(lower_layer->lslices, scale_(0.5)));
+        if (cluster_boundary.empty()) continue;
         double dist_max = 0;
         Points cluster_pts;
         for (auto& poly : cluster.merged_poly)
@@ -1068,9 +1073,11 @@ void TreeSupport::detect_overhangs(bool detect_first_sharp_tail_only)
                 auto p_overhang = it->second;
                 m_object->get_layer(layer_nr)->cantilevers.emplace_back(*p_overhang);
             }
+            max_cantilevel_dist = std::max(max_cantilevel_dist, dist_max);
             cluster.is_cantilever = true;
         }
     }
+    BOOST_LOG_TRIVIAL(info) << "max_cantilevel_dist=" << max_cantilevel_dist;
 
     if (is_auto(stype) && g_config_remove_small_overhangs) {
         if (blockers.size() < m_object->layer_count())

src/libslic3r/TreeSupport.hpp

@@ -380,6 +380,7 @@ public:
     bool  has_overhangs = false;
     bool  has_sharp_tails = false;
     bool  has_cantilever = false;
+    double max_cantilevel_dist = 0;
     SupportType support_type;
     SupportMaterialStyle support_style;