Merge branch 'main' into belt/baseChanges

src/libslic3r/Support/TreeSupport.cpp

@@ -2177,9 +2177,10 @@ void TreeSupport::draw_circles()
                         if (!area.empty()) has_circle_node = true;
                         if (node.need_extra_wall) need_extra_wall = true;
 
-                        // merge overhang to get a smoother interface surface
-                        // Do not merge when buildplate_only is on, because some underneath nodes may have been deleted.
-                        if (top_interface_layers > 0 && node.support_roof_layers_below > 0 && !on_buildplate_only && !node.is_sharp_tail) {
+                        // Merge the overhang into the roof area so tree tips can still produce
+                        // a continuous support interface. Suppressing this for build-plate-only
+                        // support drops the roof polygons entirely in valid tree branches.
+                        if (top_interface_layers > 0 && node.support_roof_layers_below > 0 && !node.is_sharp_tail) {
                             ExPolygons overhang_expanded;
                             if (node.overhang.contour.size() > 100 || node.overhang.holes.size()>1)
                                 overhang_expanded.emplace_back(node.overhang);
@@ -2222,6 +2223,17 @@ void TreeSupport::draw_circles()
                 roof_1st_layer = diff_ex(roof_1st_layer, ClipperUtils::clip_clipper_polygons_with_subject_bbox(roof_areas,get_extents(roof_1st_layer)));
                 roof_1st_layer = intersection_ex(roof_1st_layer, m_machine_border);
 
+                // Build-plate-only pruning can collapse the roof stack down to a single
+                // printable layer. In that case we still need to emit an interface layer
+                // instead of downgrading the last roof-adjacent layer to base support.
+                if (on_buildplate_only && top_interface_layers > 0 && roof_areas.empty() && !roof_1st_layer.empty()) {
+                    append(roof_areas, roof_1st_layer);
+                    roof_1st_layer.clear();
+                    max_layers_above_roof = std::max(max_layers_above_roof, max_layers_above_roof1);
+                    max_layers_above_roof1 = 0;
+                    interface_id = obj_layer_nr % top_interface_layers;
+                }
+
                 ExPolygons roofs; append(roofs, roof_1st_layer); append(roofs, roof_areas);append(roofs, roof_gap_areas);
                 base_areas = diff_ex(base_areas, ClipperUtils::clip_clipper_polygons_with_subject_bbox(roofs, get_extents(base_areas)));
                 base_areas = intersection_ex(base_areas, m_machine_border);