Add functional nonplanar code ported from https://github.com/DrEricEbert/Slic3r_NonPlanar_Slicing

src/libslic3r/CMakeLists.txt

@@ -221,6 +221,10 @@ set(SLIC3R_SOURCES
     MutablePriorityQueue.hpp
     NormalUtils.cpp
     NormalUtils.hpp
+    NonplanarFacet.cpp
+    NonplanarFacet.hpp
+    NonplanarSurface.cpp
+    NonplanarSurface.hpp
     NSVGUtils.cpp
     NSVGUtils.hpp
     ObjectID.cpp

src/libslic3r/ExPolygon.cpp

@@ -418,7 +418,7 @@ bool has_duplicate_points(const ExPolygons &expolys)
 {
 #if 1
     // Check globally.
-#if 0
+#if 1
     // Detect duplicates by sorting with quicksort. It is quite fast, but ankerl::unordered_dense is around 1/4 faster.
     Points allpts;
     allpts.reserve(count_points(expolys));

src/libslic3r/ExtrusionEntity.hpp

@@ -10,6 +10,8 @@
 #include <string_view>
 #include <numeric>
 
+#include <boost/variant.hpp>
+
 namespace Slic3r {
 
 class ExPolygon;
@@ -67,6 +69,8 @@ public:
     float width;
     // Height of the extrusion, used for visualization purposes.
     float height;
+    /// distance to surface layer in nonplanar extrusions -1.0 if not part of nonplanar extrusion
+    float distance_to_top = -1.0;
 
     ExtrusionPath(ExtrusionRole role) : mm3_per_mm(-1), width(-1), height(-1), m_role(role) {}
     ExtrusionPath(ExtrusionRole role, double mm3_per_mm, float width, float height) : mm3_per_mm(mm3_per_mm), width(width), height(height), m_role(role) {}
@@ -122,6 +126,11 @@ private:
     ExtrusionRole m_role;
 };
 
+class ExtrusionPath3 : public ExtrusionPath
+{
+    Polyline3 polyline;
+};
+
 class ExtrusionPathOriented : public ExtrusionPath
 {
 public:

src/libslic3r/ExtrusionEntityCollection.cpp

@@ -1,5 +1,7 @@
 #include "ExtrusionEntityCollection.hpp"
 #include "ShortestPath.hpp"
+#include "BoundingBox.hpp"
+#include "SVG.hpp"
 #include <algorithm>
 #include <cmath>
 #include <map>
@@ -152,4 +154,17 @@ double ExtrusionEntityCollection::min_mm3_per_mm() const
     return min_mm3_per_mm;
 }
 
+void ExtrusionEntityCollection::export_to_svg(const char *path) const
+{
+    BoundingBox bbox;
+    for (const ExtrusionEntity *entity : this->entities)
+        bbox.merge(get_extents(entity->as_polylines()));
+
+    SVG svg(path, bbox);
+    for (const ExtrusionEntity *entity : this->entities)
+        svg.draw(entity->as_polylines(), "black", scale_(0.1f));
+
+    svg.Close(); 
+}
+
 }

src/libslic3r/ExtrusionEntityCollection.hpp

@@ -124,6 +124,7 @@ public:
     ExtrusionEntityCollection flatten(bool preserve_ordering = false) const;
     double min_mm3_per_mm() const override;
     double total_volume() const override { double volume=0.; for (const auto& ent : entities) volume+=ent->total_volume(); return volume; }
+    void   export_to_svg(const char *path) const;
 
     // Following methods shall never be called on an ExtrusionEntityCollection.
     Polyline as_polyline() const override {

src/libslic3r/ExtrusionRole.cpp

@@ -19,7 +19,9 @@ GCodeExtrusionRole extrusion_role_to_gcode_extrusion_role(ExtrusionRole role)
     }
     if (role == ExtrusionRole::InternalInfill)      return GCodeExtrusionRole::InternalInfill;
     if (role == ExtrusionRole::SolidInfill)         return GCodeExtrusionRole::SolidInfill;
+    if (role == ExtrusionRole::SolidInfillNonplanar) return GCodeExtrusionRole::SolidInfillNonplanar;
     if (role == ExtrusionRole::TopSolidInfill)      return GCodeExtrusionRole::TopSolidInfill;
+    if (role == ExtrusionRole::TopSolidInfillNonplanar) return GCodeExtrusionRole::TopSolidInfillNonplanar;
     if (role == ExtrusionRole::Ironing)             return GCodeExtrusionRole::Ironing;
     if (role == ExtrusionRole::BridgeInfill)        return GCodeExtrusionRole::BridgeInfill;
     if (role == ExtrusionRole::GapFill)             return GCodeExtrusionRole::GapFill;
@@ -40,7 +42,9 @@ std::string gcode_extrusion_role_to_string(GCodeExtrusionRole role)
         case GCodeExtrusionRole::OverhangPerimeter            : return L("Overhang perimeter");
         case GCodeExtrusionRole::InternalInfill               : return L("Internal infill");
         case GCodeExtrusionRole::SolidInfill                  : return L("Solid infill");
+        case GCodeExtrusionRole::SolidInfillNonplanar         : return L("Nonplanar solid infill");
         case GCodeExtrusionRole::TopSolidInfill               : return L("Top solid infill");
+        case GCodeExtrusionRole::TopSolidInfillNonplanar      : return L("Nonplanar top solid infill");
         case GCodeExtrusionRole::Ironing                      : return L("Ironing");
         case GCodeExtrusionRole::BridgeInfill                 : return L("Bridge infill");
         case GCodeExtrusionRole::GapFill                      : return L("Gap fill");
@@ -66,8 +70,12 @@ GCodeExtrusionRole string_to_gcode_extrusion_role(const std::string_view role)
         return GCodeExtrusionRole::InternalInfill;
     else if (role == L("Solid infill"))
         return GCodeExtrusionRole::SolidInfill;
+    else if (role == L("Nonplanar solid infill"))
+        return GCodeExtrusionRole::SolidInfill;
     else if (role == L("Top solid infill"))
         return GCodeExtrusionRole::TopSolidInfill;
+    else if (role == L("Nonplanar top solid infill"))
+        return GCodeExtrusionRole::TopSolidInfillNonplanar;
     else if (role == L("Ironing"))
         return GCodeExtrusionRole::Ironing;
     else if (role == L("Bridge infill"))

src/libslic3r/ExtrusionRole.hpp

@@ -26,6 +26,7 @@ enum class ExtrusionRoleModifier : uint16_t {
     Solid,
     Ironing,
     Bridge,
+    Nonplanar,
 // 3) Special types
     // Indicator that the extrusion role was mixed from multiple differing extrusion roles,
     // for example from Support and SupportInterface.
@@ -55,9 +56,11 @@ struct ExtrusionRole : public ExtrusionRoleModifiers
     static constexpr const ExtrusionRoleModifiers InternalInfill{ ExtrusionRoleModifier::Infill };
     // Solid internal infill.
     static constexpr const ExtrusionRoleModifiers SolidInfill{ ExtrusionRoleModifier::Infill | ExtrusionRoleModifier::Solid };
+    static constexpr const ExtrusionRoleModifiers SolidInfillNonplanar{ ExtrusionRoleModifier::Infill | ExtrusionRoleModifier::Solid | ExtrusionRoleModifier::Nonplanar };
     // Top solid infill (visible).
     //FIXME why there is no bottom solid infill type?
     static constexpr const ExtrusionRoleModifiers TopSolidInfill{ ExtrusionRoleModifier::Infill | ExtrusionRoleModifier::Solid | ExtrusionRoleModifier::External };
+    static constexpr const ExtrusionRoleModifiers TopSolidInfillNonplanar{ ExtrusionRoleModifier::Infill | ExtrusionRoleModifier::Solid | ExtrusionRoleModifier::External | ExtrusionRoleModifier::Nonplanar };
     // Ironing infill at the top surfaces.
     static constexpr const ExtrusionRoleModifiers Ironing{ ExtrusionRoleModifier::Infill | ExtrusionRoleModifier::Solid | ExtrusionRoleModifier::Ironing | ExtrusionRoleModifier::External };
     // Visible bridging infill at the bottom of an object.
@@ -84,6 +87,7 @@ struct ExtrusionRole : public ExtrusionRoleModifiers
     bool is_solid_infill() const { return this->is_infill() && this->ExtrusionRoleModifiers::has(ExtrusionRoleModifier::Solid); }
     bool is_external() const { return this->ExtrusionRoleModifiers::has(ExtrusionRoleModifier::External); }
     bool is_bridge() const { return this->ExtrusionRoleModifiers::has(ExtrusionRoleModifier::Bridge); }
+    bool is_nonplanar() const { return this->ExtrusionRoleModifiers::has(ExtrusionRoleModifier::Nonplanar); }
 
     bool is_support() const { return this->ExtrusionRoleModifiers::has(ExtrusionRoleModifier::Support); }
     bool is_support_base() const { return this->is_support() && ! this->is_external(); }
@@ -108,7 +112,9 @@ enum class GCodeExtrusionRole : uint8_t {
     OverhangPerimeter,
     InternalInfill,
     SolidInfill,
+    SolidInfillNonplanar,
     TopSolidInfill,
+    TopSolidInfillNonplanar,
     Ironing,
     BridgeInfill,
     GapFill,

src/libslic3r/Fill/Fill.cpp

@@ -2,6 +2,8 @@
 #include <stdio.h>
 #include <memory>
 
+#include "SVG.hpp"
+
 #include "../ClipperUtils.hpp"
 #include "../Geometry.hpp"
 #include "../Layer.hpp"
@@ -144,7 +146,7 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
 		        if (surface.is_solid()) {
 		            params.density = 100.f;
 					//FIXME for non-thick bridges, shall we allow a bottom surface pattern?
-		            params.pattern = (surface.is_external() && ! is_bridge) ? 
+		            params.pattern = (surface.is_external() && ! is_bridge && !surface.is_nonplanar()) ? 
 						(surface.is_top() ? region_config.top_fill_pattern.value : region_config.bottom_fill_pattern.value) :
 		                fill_type_monotonic(region_config.top_fill_pattern) ? ipMonotonic : ipRectilinear;
 		        } else if (params.density <= 0)
@@ -154,7 +156,10 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
 		            is_bridge ?
 		                ExtrusionRole::BridgeInfill :
 		                (surface.is_solid() ?
-		                    (surface.is_top() ? ExtrusionRole::TopSolidInfill : ExtrusionRole::SolidInfill) :
+		                    (surface.is_top() ? 
+								(surface.is_nonplanar() ? ExtrusionRole::TopSolidInfillNonplanar : ExtrusionRole::TopSolidInfill) : 
+								(surface.is_nonplanar() ? ExtrusionRole::SolidInfillNonplanar : ExtrusionRole::SolidInfill)
+							) :
 							ExtrusionRole::InternalInfill);
 		        params.bridge_angle = float(surface.bridge_angle);
 		        params.angle 		= float(Geometry::deg2rad(region_config.fill_angle.value));
@@ -252,7 +257,7 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
 			if (! surface_fill.expolygons.empty()) {
     			distance_between_surfaces = std::max(distance_between_surfaces, surface_fill.params.flow.scaled_spacing());
 				append((surface_fill.surface.surface_type == stInternalVoid) ? voids : surfaces_polygons, to_polygons(surface_fill.expolygons));
-				if (surface_fill.surface.surface_type == stInternalSolid)
+				if (surface_fill.surface.is_internal_solid())
 					region_internal_infill = (int)surface_fill.region_id;
 				if (surface_fill.surface.is_solid())
 					region_solid_infill = (int)surface_fill.region_id;
@@ -281,7 +286,7 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
 				region_id = region_some_infill;
 			const LayerRegion& layerm = *layer.regions()[region_id];
 	        for (SurfaceFill &surface_fill : surface_fills)
-	        	if (surface_fill.surface.surface_type == stInternalSolid && std::abs(layer.height - surface_fill.params.flow.height()) < EPSILON) {
+				if ((surface_fill.surface.is_internal_solid()) && std::abs(layer.height - surface_fill.params.flow.height()) < EPSILON) {
 					internal_solid_fill = &surface_fill;
 					break;
 				}
@@ -309,7 +314,7 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
     // Use ipEnsuring pattern for all internal Solids.
     {
         for (size_t surface_fill_id = 0; surface_fill_id < surface_fills.size(); ++surface_fill_id)
-            if (SurfaceFill &fill = surface_fills[surface_fill_id]; fill.surface.surface_type == stInternalSolid) {
+            if (SurfaceFill &fill = surface_fills[surface_fill_id]; fill.surface.is_internal_solid()) {
                 fill.params.pattern = ipEnsuring;
             }
     }
@@ -449,10 +454,12 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
 #ifdef SLIC3R_DEBUG_SLICE_PROCESSING
 	{
 		static int iRun = 0;
-		export_group_fills_to_svg(debug_out_path("Layer-fill_surfaces-10_fill-final-%d.svg", iRun ++).c_str(), surface_fills);
+		export_group_fills_to_svg(debug_out_path("Layer-%d-fill_surfaces-10_fill-final-%d.svg", id(), iRun ++).c_str(), surface_fills);
 	}
 #endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
 
+	BOOST_LOG_TRIVIAL(trace) << "make_fills: found " << surface_fills.size() << " surfaces to fill for layer " << id();
+
 	size_t first_object_layer_id = this->object()->get_layer(0)->id();
     for (SurfaceFill &surface_fill : surface_fills) {
         // Create the filler object.
@@ -519,6 +526,7 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
                 else
 				    polylines = f->fill_surface(&surface_fill.surface, params);
 			} catch (InfillFailedException &) {
+				BOOST_LOG_TRIVIAL(trace) << "make_fills: InfillFailedException!";
 			}
             if (!polylines.empty() || !thick_polylines.empty()) {
                 // calculate actual flow from spacing (which might have been adjusted by the infill
@@ -562,6 +570,8 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
                         flow_mm3_per_mm, float(flow_width), surface_fill.params.flow.height());
                 }
                 insert_fills_into_islands(*this, uint32_t(surface_fill.region_id), fill_begin, uint32_t(layerm.fills().size()));
+		    } else {
+				BOOST_LOG_TRIVIAL(trace) << "make_fills: no infill was generated for layer " << id();
 			}
 		}
     }
@@ -854,7 +864,7 @@ void Layer::make_ironing()
 						polygons_append(polys, surface.expolygon);
 				} else {
 					for (const Surface &surface : ironing_params.layerm->slices())
-						if (surface.surface_type == stTop || (iron_everything && surface.surface_type == stBottom))
+						if (surface.is_top() || (iron_everything && surface.surface_type == stBottom))
 							// stBottomBridge is not being ironed on purpose, as it would likely destroy the bridges.
 							polygons_append(polys, surface.expolygon);
 				}
@@ -862,7 +872,7 @@ void Layer::make_ironing()
 					// Add solid fill surfaces. This may not be ideal, as one will not iron perimeters touching these
 					// solid fill surfaces, but it is likely better than nothing.
 					for (const Surface &surface : ironing_params.layerm->fill_surfaces())
-						if (surface.surface_type == stInternalSolid)
+						if (surface.is_internal_solid())
 							polygons_append(infills, surface.expolygon);
 				}
 			}

src/libslic3r/GCode.cpp

@@ -2459,7 +2459,10 @@ void GCode::process_layer_single_object(
     };
 
     ExtrusionEntitiesPtr temp_fill_extrusions;
-    if (const Layer *layer = layer_to_print.object_layer; layer)
+    if (const Layer *layer = layer_to_print.object_layer; layer) {
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+        layer->export_lslices_polygons_to_svg_debug("process_gcode_layer");
+#endif
         for (size_t idx : layer->lslice_indices_sorted_by_print_order) {
             const LayerSlice &lslice = layer->lslices_ex[idx];
             auto extrude_infill_range = [&](
@@ -2472,15 +2475,25 @@ void GCode::process_layer_single_object(
                 for (auto it_fill_range = it_fill_ranges_begin; it_fill_range != it_fill_ranges_end; ++ it_fill_range) {
                     assert(it_fill_range->region() == it_fill_ranges_begin->region());
                     for (uint32_t fill_id : *it_fill_range) {
-                        assert(dynamic_cast<ExtrusionEntityCollection*>(fills.entities[fill_id]));
+                        auto *eec = static_cast<ExtrusionEntityCollection*>(fills.entities[fill_id]);
-                        if (auto *eec = static_cast<ExtrusionEntityCollection*>(fills.entities[fill_id]);
+                        assert(eec);
-                            (eec->role() == ExtrusionRole::Ironing) == ironing && shall_print_this_extrusion_collection(eec, region)) {
+                        if ((eec->role() == ExtrusionRole::Ironing) == ironing && shall_print_this_extrusion_collection(eec, region)) {
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+                                static int extrude_infill_range_run = 0;
+                                eec->export_to_svg(debug_out_path("Layer-%d_gcode-extrude_infill_range-shall-be-printed-%u.svg", layerm.layer()->id(), extrude_infill_range_run++).c_str());
+#endif
                             if (eec->can_reverse())
                                 // Flatten the infill collection for better path planning.
-                                for (auto *ee : eec->entities)
+                                for (auto *ee : eec->entities) {
                                     temp_fill_extrusions.emplace_back(ee);
+                                }
                             else
                                 temp_fill_extrusions.emplace_back(eec);
+                        } else {
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+                                static int iRun = 0;
+                                eec->export_to_svg(debug_out_path("Layer-%d_gcode-extrude_infill_range-shall-not-be-printed-%u.svg", layerm.layer()->id(), iRun++).c_str());
+#endif
                         }
                     }
                 }
@@ -2491,17 +2504,30 @@ void GCode::process_layer_single_object(
                     // Will parallel access of initial G-code preview to these extrusions while reordering them at backend cause issues?
                     chain_and_reorder_extrusion_entities(temp_fill_extrusions, &m_last_pos);
                     const auto extrusion_name = ironing ? "ironing"sv : "infill"sv;
-                    for (const ExtrusionEntity *fill : temp_fill_extrusions)
+                    for (const ExtrusionEntity *fill : temp_fill_extrusions) {
                         if (auto *eec = dynamic_cast<const ExtrusionEntityCollection*>(fill); eec) {
-                            for (const ExtrusionEntity *ee : eec->chained_path_from(m_last_pos).entities)
+                            for (const ExtrusionEntity *ee : eec->chained_path_from(m_last_pos).entities) {
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+                                static int iRun = 0;
+                                eec->export_to_svg(debug_out_path("Layer-%d_gcode-extrude_infill_range-collection-%u.svg", layerm.layer()->id(), iRun++).c_str());
+#endif
                                 gcode += this->extrude_entity(*ee, extrusion_name);
-                        } else
+                            }
+                        } else {
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+                                static int iRun = 0;
+                                export_to_svg(debug_out_path("Layer-%d_gcode-extrude_infill_range-entity-%u.svg", layerm.layer()->id(), iRun++).c_str(), 
+                                    fill->as_polyline(), get_extents(layerm.slices().surfaces), scale_(0.1f));
+#endif
                             gcode += this->extrude_entity(*fill, extrusion_name);
                         }
+                    }
+                }
             };
 
             //FIXME order islands?
             // Sequential tool path ordering of multiple parts within the same object, aka. perimeter tracking (#5511)
+            BOOST_LOG_TRIVIAL(trace) << "Generating GCode for layer " << layer->id() << " - slice " << idx << " has " << lslice.islands.size() << " islands";
             for (const LayerIsland &island : lslice.islands) {
                 auto process_perimeters = [&]() {
                     const LayerRegion &layerm = *layer->get_region(island.perimeters.region());
@@ -2510,9 +2536,13 @@ void GCode::process_layer_single_object(
                     const PrintRegion &region = print.get_print_region(layerm.region().print_region_id());
                     bool first = true;
                     for (uint32_t perimeter_id : island.perimeters) {
-                        assert(dynamic_cast<const ExtrusionEntityCollection*>(layerm.perimeters().entities[perimeter_id]));
+                        const auto *eec = static_cast<const ExtrusionEntityCollection*>(layerm.perimeters().entities[perimeter_id]);
-                        if (const auto *eec = static_cast<const ExtrusionEntityCollection*>(layerm.perimeters().entities[perimeter_id]);
+                        assert(eec);
-                            shall_print_this_extrusion_collection(eec, region)) {
+                        if (shall_print_this_extrusion_collection(eec, region)) {
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+                                static int iRun = 0;
+                                eec->export_to_svg(debug_out_path("Layer-%d_gcode-process_perimeters-%u.svg", layerm.layer()->id(), iRun++).c_str());
+#endif
                             // This may not apply to Arachne, but maybe the Arachne gap fill should disable reverse as well?
                             // assert(! eec->can_reverse());
                             if (first) {
@@ -2520,9 +2550,15 @@ void GCode::process_layer_single_object(
                                 init_layer_delayed();
                                 m_config.apply(region.config());
                             }
-                            for (const ExtrusionEntity *ee : *eec)
+                            for (const ExtrusionEntity *ee : *eec) {
                                 gcode += this->extrude_entity(*ee, comment_perimeter, -1.);
                             }
+                        } else {
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+                                static int iRun = 0;
+                                eec->export_to_svg(debug_out_path("Layer-%d_gcode-process_perimeters-not-printed-%u.svg", layerm.layer()->id(), iRun++).c_str());
+#endif
+                        }
                     }
                 };
                 auto process_infill = [&]() {
@@ -2535,6 +2571,7 @@ void GCode::process_layer_single_object(
                         it = it_end;
                     }
                 };
+                BOOST_LOG_TRIVIAL(trace) << "Generating GCode for layer " << layer->id() << " island - " << island.fills.size() << " fills, " << island.perimeters.size() << " perimeters.";
                 if (print.config().infill_first) {
                     process_infill();
                     process_perimeters();
@@ -2558,6 +2595,7 @@ void GCode::process_layer_single_object(
                 }
             }
         }
+    }
     if (! first && this->config().gcode_label_objects)
         gcode += std::string("; stop printing object ") + print_object.model_object()->name + " id:" + std::to_string(object_id) + " copy " + std::to_string(print_instance.instance_id) + "\n";
 }
@@ -2793,6 +2831,11 @@ std::string GCode::extrude_multi_path(ExtrusionMultiPath multipath, const std::s
 
 std::string GCode::extrude_entity(const ExtrusionEntity &entity, const std::string_view description, double speed)
 {
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+    static int extrude_infill_range_run = 0;
+    export_to_svg(debug_out_path("gcode-extrude_entity-%u.svg", extrude_infill_range_run++).c_str(), 
+        entity.as_polyline(), get_extents(entity.as_polyline()), scale_(0.1f));
+#endif
     if (const ExtrusionPath* path = dynamic_cast<const ExtrusionPath*>(&entity))
         return this->extrude_path(*path, description, speed);
     else if (const ExtrusionMultiPath* multipath = dynamic_cast<const ExtrusionMultiPath*>(&entity))
@@ -2943,7 +2986,7 @@ std::string GCode::_extrude(const ExtrusionPath &path, const std::string_view de
             acceleration = m_config.first_layer_acceleration_over_raft.value;
         } else if (m_config.bridge_acceleration.value > 0 && path.role().is_bridge()) {
             acceleration = m_config.bridge_acceleration.value;
-        } else if (m_config.top_solid_infill_acceleration > 0 && path.role() == ExtrusionRole::TopSolidInfill) {
+        } else if (m_config.top_solid_infill_acceleration > 0 && (path.role() == ExtrusionRole::TopSolidInfill || path.role() == ExtrusionRole::TopSolidInfillNonplanar)) {
             acceleration = m_config.top_solid_infill_acceleration.value;
         } else if (m_config.solid_infill_acceleration > 0 && path.role().is_solid_infill()) {
             acceleration = m_config.solid_infill_acceleration.value;
@@ -2976,9 +3019,9 @@ std::string GCode::_extrude(const ExtrusionPath &path, const std::string_view de
             speed = m_config.get_abs_value("bridge_speed");
         } else if (path.role() == ExtrusionRole::InternalInfill) {
             speed = m_config.get_abs_value("infill_speed");
-        } else if (path.role() == ExtrusionRole::SolidInfill) {
+        } else if (path.role() == ExtrusionRole::SolidInfill || path.role() == ExtrusionRole::SolidInfillNonplanar) {
             speed = m_config.get_abs_value("solid_infill_speed");
-        } else if (path.role() == ExtrusionRole::TopSolidInfill) {
+        } else if (path.role() == ExtrusionRole::TopSolidInfill || path.role() == ExtrusionRole::TopSolidInfillNonplanar) {
             speed = m_config.get_abs_value("top_solid_infill_speed");
         } else if (path.role() == ExtrusionRole::Ironing) {
             speed = m_config.get_abs_value("ironing_speed");
@@ -3118,15 +3161,15 @@ std::string GCode::_extrude(const ExtrusionPath &path, const std::string_view de
             comment = description;
             comment += description_bridge;
         }
-        Vec2d prev = this->point_to_gcode_quantized(path.polyline.points.front());
+        Vec3d prev3 = this->point3_to_gcode_quantized(path.polyline.points.front());
         auto  it   = path.polyline.points.begin();
         auto  end  = path.polyline.points.end();
         for (++ it; it != end; ++ it) {
-            Vec2d p = this->point_to_gcode_quantized(*it);
+            Vec3d p3 = this->point3_to_gcode_quantized(*it);
-            const double line_length = (p - prev).norm();
+            const double line_length = (p3 - prev3).norm();
             path_length += line_length;
-            gcode += m_writer.extrude_to_xy(p, e_per_mm * line_length, comment);
+            gcode += m_writer.extrude_to_xyz(p3, e_per_mm * line_length, comment);
-            prev = p;
+            prev3 = p3;
         }
     } else {
         std::string marked_comment;
@@ -3138,13 +3181,13 @@ std::string GCode::_extrude(const ExtrusionPath &path, const std::string_view de
         double last_set_fan_speed = new_points[0].fan_speed;
         gcode += m_writer.set_speed(last_set_speed, "", cooling_marker_setspeed_comments);
         gcode += "\n;_SET_FAN_SPEED" + std::to_string(int(last_set_fan_speed)) + "\n";
-        Vec2d prev = this->point_to_gcode_quantized(new_points[0].p);
+        Vec3d prev3 = this->point3_to_gcode_quantized(new_points[0].p);
         for (size_t i = 1; i < new_points.size(); i++) {
             const ProcessedPoint &processed_point = new_points[i];
-            Vec2d                 p               = this->point_to_gcode_quantized(processed_point.p);
+            Vec3d                 p3              = this->point3_to_gcode_quantized(processed_point.p);
-            const double          line_length     = (p - prev).norm();
+            const double          line_length     = (p3 - prev3).norm();
-            gcode += m_writer.extrude_to_xy(p, e_per_mm * line_length, marked_comment);
+            gcode += m_writer.extrude_to_xyz(p3, e_per_mm * line_length, marked_comment);
-            prev             = p;
+            prev3             = p3;
             double new_speed = processed_point.speed * 60.0;
             if (last_set_speed != new_speed) {
                 gcode += m_writer.set_speed(new_speed, "", cooling_marker_setspeed_comments);
@@ -3186,6 +3229,8 @@ std::string GCode::travel_to(const Point &point, ExtrusionRole role, std::string
 
     // check whether a straight travel move would need retraction
     bool needs_retraction             = this->needs_retraction(travel, role);
+    // check whether we need to move to a different z layer
+    bool needs_zmove                  = this->needs_zmove(travel);
     // check whether wipe could be disabled without causing visible stringing
     bool could_be_wipe_disabled       = false;
     // Save state of use_external_mp_once for the case that will be needed to call twice m_avoid_crossing_perimeters.travel_to.
@@ -3232,10 +3277,20 @@ std::string GCode::travel_to(const Point &point, ExtrusionRole role, std::string
     // use G1 because we rely on paths being straight (G0 may make round paths)
     if (travel.size() >= 2) {
 
+        // Move Z up if necessary
+        if (needs_zmove) {
+            gcode += m_writer.travel_to_z(this->layer()->print_z, "Move up for non planar extrusion");
+        }
+
         gcode += m_writer.set_travel_acceleration((unsigned int)(m_config.travel_acceleration.value + 0.5));
 
-        for (size_t i = 1; i < travel.size(); ++ i)
+        for (size_t i = 1; i < travel.size(); ++ i) {
+            if (needs_zmove) {
+                gcode += m_writer.travel_to_xyz(this->point3_to_gcode(travel.points[i]), comment);
+            } else {
                 gcode += m_writer.travel_to_xy(this->point_to_gcode(travel.points[i]), comment);
+            }
+        }
 
         if (! GCodeWriter::supports_separate_travel_acceleration(config().gcode_flavor)) {
             // In case that this flavor does not support separate print and travel acceleration,
@@ -3243,8 +3298,18 @@ std::string GCode::travel_to(const Point &point, ExtrusionRole role, std::string
             gcode += m_writer.set_travel_acceleration((unsigned int)(m_config.travel_acceleration.value + 0.5));
         }
 
+        if (needs_zmove) {
+            float move_z = unscale<double>(point.nonplanar_z);
+            if(point.nonplanar_z == -1) {
+                move_z = this->layer()->print_z;
+            }
+            gcode += m_writer.travel_to_z(move_z, "Move down for non planar extrusion");
+        }
+
         this->set_last_pos(travel.points.back());
     }
+
+
     return gcode;
 }
 
@@ -3287,6 +3352,24 @@ bool GCode::needs_retraction(const Polyline &travel, ExtrusionRole role)
     return true;
 }
 
+bool
+GCode::needs_zmove(const Polyline &travel)
+{
+    if (travel.length() < scale_(1.0)) {
+        // skip zmove if the move is shorter 1 mm
+        return false;
+    }
+
+    //check if any point in travel is below the layer z
+    for (Point p : travel.points)
+    {
+        if ((p.nonplanar_z != -1) && (p.nonplanar_z < scale_(this->layer()->print_z)))
+            return true;
+    }
+
+    return false;
+}
+
 std::string GCode::retract(bool toolchange)
 {
     std::string gcode;
@@ -3421,12 +3504,28 @@ Vec2d GCode::point_to_gcode(const Point &point) const
     return unscaled<double>(point) + m_origin - extruder_offset;
 }
 
+// convert a model-space scaled point into G-code coordinates
+Vec3d GCode::point3_to_gcode(const Point &point) const
+{
+    Vec2d extruder_offset = EXTRUDER_CONFIG(extruder_offset);
+    double p_x = unscaled<double>(point.x()) + m_origin.x() - extruder_offset.x();
+    double p_y = unscaled<double>(point.y()) + m_origin.y() - extruder_offset.y();
+    double p_z = point.nonplanar_z == -1 ? this->layer()->print_z : unscale<double>(point.nonplanar_z);
+    return { p_x, p_y, p_z };
+}
+
 Vec2d GCode::point_to_gcode_quantized(const Point &point) const
 {
     Vec2d p = this->point_to_gcode(point);
     return { GCodeFormatter::quantize_xyzf(p.x()), GCodeFormatter::quantize_xyzf(p.y()) };
 }
 
+Vec3d GCode::point3_to_gcode_quantized(const Point &point) const
+{
+    Vec3d p = this->point3_to_gcode(point);
+    return { GCodeFormatter::quantize_xyzf(p.x()), GCodeFormatter::quantize_xyzf(p.y()), GCodeFormatter::quantize_xyzf(p.z()) };
+}
+
 // convert a model-space scaled point into G-code coordinates
 Point GCode::gcode_to_point(const Vec2d &point) const
 {
@@ -3435,7 +3534,6 @@ Point GCode::gcode_to_point(const Vec2d &point) const
         // This function may be called at the very start from toolchange G-code when the extruder is not assigned yet.
         pt += m_config.extruder_offset.get_at(extruder->id());
     return scaled<coord_t>(pt);
-        
 }
 
 }   // namespace Slic3r

src/libslic3r/GCode.hpp

@@ -166,8 +166,10 @@ public:
     const Point&    last_pos() const { return m_last_pos; }
     // Convert coordinates of the active object to G-code coordinates, possibly adjusted for extruder offset.
     Vec2d           point_to_gcode(const Point &point) const;
+    Vec3d           point3_to_gcode(const Point &point) const;
     // Convert coordinates of the active object to G-code coordinates, possibly adjusted for extruder offset and quantized to G-code resolution.
     Vec2d           point_to_gcode_quantized(const Point &point) const;
+    Vec3d           point3_to_gcode_quantized(const Point &point) const;
     Point           gcode_to_point(const Vec2d &point) const;
     const FullPrintConfig &config() const { return m_config; }
     const Layer*    layer() const { return m_layer; }
@@ -326,6 +328,7 @@ private:
 
     std::string     travel_to(const Point &point, ExtrusionRole role, std::string comment);
     bool            needs_retraction(const Polyline &travel, ExtrusionRole role = ExtrusionRole::None);
+    bool            needs_zmove(const Polyline &travel);
     std::string     retract(bool toolchange = false);
     std::string     unretract() { return m_writer.unlift() + m_writer.unretract(); }
     std::string     set_extruder(unsigned int extruder_id, double print_z);

src/libslic3r/GCodeWriter.cpp

@@ -274,7 +274,7 @@ std::string GCodeWriter::travel_to_xyz(const Vec3d &point, const std::string &co
     // FIXME: This function was not being used when travel_speed_z was separated (bd6badf).
     // Calculation of feedrate was not updated accordingly. If you want to use
     // this function, fix it first.
-    std::terminate();
+    // std::terminate();
 
     /*  If target Z is lower than current Z but higher than nominal Z we
         don't perform the Z move but we only move in the XY plane and
@@ -360,16 +360,16 @@ std::string GCodeWriter::extrude_to_xy(const Vec2d &point, double dE, const std:
     return w.string();
 }
 
-#if 0
+#if 1
 std::string GCodeWriter::extrude_to_xyz(const Vec3d &point, double dE, const std::string &comment)
 {
     m_pos = point;
     m_lifted = 0;
-    m_extruder->extrude(dE);
+    //m_extruder->extrude(dE);
     
     GCodeG1Formatter w;
     w.emit_xyz(point);
-    w.emit_e(m_extrusion_axis, m_extruder->E());
+    w.emit_e(m_extrusion_axis, m_extruder->extrude(dE).second);
     w.emit_comment(this->config.gcode_comments, comment);
     return w.string();
 }

src/libslic3r/GCodeWriter.hpp

@@ -62,7 +62,7 @@ public:
     std::string travel_to_z(double z, const std::string &comment = std::string());
     bool        will_move_z(double z) const;
     std::string extrude_to_xy(const Vec2d &point, double dE, const std::string &comment = std::string());
-//    std::string extrude_to_xyz(const Vec3d &point, double dE, const std::string &comment = std::string());
+    std::string extrude_to_xyz(const Vec3d &point, double dE, const std::string &comment = std::string());
     std::string retract(bool before_wipe = false);
     std::string retract_for_toolchange(bool before_wipe = false);
     std::string unretract();

src/libslic3r/Geometry.cpp

@@ -746,4 +746,74 @@ bool trafos_differ_in_rotation_by_z_and_mirroring_by_xy_only(const Transform3d &
     return std::abs(d * d) < EPSILON * lx2 * ly2;
 }
 
+bool
+Point_in_triangle(Vec2f pt, Vec2f v1, Vec2f v2, Vec2f v3)
+{
+    //Check if point is right of every edge
+    if (sign(pt, v1, v2) <= 0.0f) return false;
+    if (sign(pt, v2, v3) <= 0.0f) return false;
+    if (sign(pt, v3, v1) <= 0.0f) return false;
+
+    return true;
+}
+
+//https://graphics.stanford.edu/~mdfisher/Code/Engine/Plane.cpp.html
+coord_t
+Project_point_on_plane(Vec3f v1, Vec3f n, Point pt)
+{
+    //if no intersection leave point unchanged (should never happen)
+    if(n.z() == 0) {
+        return -1;
+    }
+    
+    //unscale point for calculations
+    float px = unscale<float>(pt.x());
+    float py = unscale<float>(pt.y());
+    float pz = 0;
+
+    //Calculate space plane
+    float d = -(v1.x() * n.x() + v1.y() * n.y() + v1.z() * n.z());
+
+    float u = -(n.x() * px + n.y() * py + n.z() * pz + d) / n.z();
+
+    //scale up again
+    return scale_(u);
+}
+
+// http://paulbourke.net/geometry/pointlineplane/index.html
+Vec3d*
+Line_intersection(Vec3d p1, Vec3d p2, Point p3, Point p4) {
+
+    float denom = ((p4.y() - p3.y())*(p2.x() - p1.x())) -
+                  ((p4.x() - p3.x())*(p2.y() - p1.y()));
+
+    float nume_a = ((p4.x() - p3.x())*(p1.y() - p3.y())) -
+                   ((p4.y() - p3.y())*(p1.x() - p3.x()));
+
+    float nume_b = ((p2.x() - p1.x())*(p1.y() - p3.y())) -
+                   ((p2.y() - p1.y())*(p1.x() - p3.x()));
+
+    if(denom == 0.0f)
+    {
+        return NULL;
+    }
+
+    float ua = nume_a / denom;
+    float ub = nume_b / denom;
+
+    if(ua >= 0.0f && ua <= 1.0f && ub >= 0.0f && ub <= 1.0f)
+    {
+        // Get the intersection point anc calculate z component
+        Vec3d* ret = new Vec3d();
+        ret->x() = p1.x() + ua*(p2.x() - p1.x());
+        ret->y() = p1.y() + ua*(p2.y() - p1.y());
+        ret->z() = p1.z() - ((sqrt((p1.x()-ret->x())*(p1.x()-ret->x()) + (p1.y()-ret->y())*(p1.y()-ret->y()))
+                  / sqrt((p1.x()-p2.x())*(p1.x()-p2.x()) + (p1.y()-p2.y())*(p1.y()-p2.y())))
+                  * (p1.z() - p2.z()));
+        return ret;
+    }
+
+    return NULL;
+}
+
 }} // namespace Slic3r::Geometry

src/libslic3r/Geometry.hpp

@@ -529,6 +529,23 @@ Vec<3, T> spheric_to_dir(const Pair &v)
     return spheric_to_dir<T>(plr, azm);
 }
 
+inline float sign(Vec2f p1, Vec2f p2, Vec2f p3)
+{
+    return (p1.x() - p3.x()) * (p2.y() - p3.y()) - (p2.x() - p3.x()) * (p1.y() - p3.y());
+}
+
+bool Point_in_triangle(Vec2f pt, Vec2f v1, Vec2f v2, Vec2f v3);
+
+//https://graphics.stanford.edu/~mdfisher/Code/Engine/Plane.cpp.html
+coord_t Project_point_on_plane(Vec3f v1, Vec3f n, Point pt);
+
+// http://paulbourke.net/geometry/pointlineplane/index.html
+Vec3d *Line_intersection(Vec3d p1, Vec3d p2, Point p3, Point p4);
+
+inline float triangle_surface(Point p1, Point p2, Point p3) {
+    return 0.5 * ((p2.x()-p1.x()) * (p3.y()-p1.y()) - (p2.y()-p1.y()) * (p3.x()-p1.x()));
+}
+
 } } // namespace Slicer::Geometry
 
 #endif

src/libslic3r/Layer.cpp

@@ -54,6 +54,8 @@ void Layer::make_slices()
         }
         // lslices are sorted by topological order from outside to inside from the clipper union used above
         this->lslices = slices;
+
+        BOOST_LOG_TRIVIAL(trace) << "make_slices layer " << id() << " found " << slices.size() << " slices";
     }
 
     this->lslice_indices_sorted_by_print_order = chain_expolygons(this->lslices);
@@ -1066,7 +1068,7 @@ void Layer::export_region_slices_to_svg(const char *path) const
 void Layer::export_region_slices_to_svg_debug(const char *name) const
 {
     static size_t idx = 0;
-    this->export_region_slices_to_svg(debug_out_path("Layer-slices-%s-%d.svg", name, idx ++).c_str());
+    this->export_region_slices_to_svg(debug_out_path("Layer-%d-slices-%s-%d.svg", id(), name, idx ++).c_str());
 }
 
 void Layer::export_region_fill_surfaces_to_svg(const char *path) const
@@ -1092,7 +1094,57 @@ void Layer::export_region_fill_surfaces_to_svg(const char *path) const
 void Layer::export_region_fill_surfaces_to_svg_debug(const char *name) const
 {
     static size_t idx = 0;
-    this->export_region_fill_surfaces_to_svg(debug_out_path("Layer-fill_surfaces-%s-%d.svg", name, idx ++).c_str());
+    this->export_region_fill_surfaces_to_svg(debug_out_path("Layer-%d-fill_surfaces-%s-%d.svg", id(), name, idx ++).c_str());
+}
+
+void Layer::export_lslices_polygons_to_svg(const char *path) const
+{
+    BoundingBox bbox;
+    for (const auto *region : m_regions)
+        for (const auto &surface : region->slices())
+            bbox.merge(get_extents(surface.expolygon));
+
+    SVG svg(path, bbox);
+    for (int i = 0; i< lslices.size(); i++)
+        svg.draw(lslices[i], "black", 1.0);
+    svg.Close();
+}
+
+// Export to "out/Layer-%name-%idx.svg" with an increasing index with every export.
+void Layer::export_lslices_polygons_to_svg_debug(const char *name) const
+{
+    static size_t idx = 0;
+    this->export_lslices_polygons_to_svg(debug_out_path("Layer-%d-lslice_polygons-%s-%d.svg", id(), name, idx ++).c_str());
+}
+
+void 
+LayerRegion::remove_nonplanar_slices(SurfaceCollection topNonplanar) {
+    Surfaces layerm_slices_surfaces(m_slices.surfaces);
+
+    //save previously detected nonplanar surfaces
+    SurfaceCollection polyNonplanar;
+    for(Surface s : m_slices.surfaces) {
+        if (s.is_nonplanar()) {
+            polyNonplanar.surfaces.push_back(s);
+        }
+    }
+
+    // clear internal surfaces
+    m_slices.clear();
+
+    // append internal surfaces again without the found topNonplanar surfaces
+    m_slices.append(
+        diff_ex(
+            union_ex(layerm_slices_surfaces), 
+            topNonplanar.surfaces, 
+            ApplySafetyOffset::No),
+        stInternal
+    );
+}
+
+void 
+LayerRegion::append_top_nonplanar_slices(SurfaceCollection topNonplanar) {
+    m_slices.append(std::move(topNonplanar));
 }
 
 BoundingBox get_extents(const LayerRegion &layer_region)

src/libslic3r/Layer.hpp

@@ -7,6 +7,7 @@
 #include "Flow.hpp"
 #include "SurfaceCollection.hpp"
 #include "ExtrusionEntityCollection.hpp"
+#include "NonplanarSurface.hpp"
 
 #include <boost/container/small_vector.hpp>
 
@@ -133,6 +134,9 @@ public:
     // (this collection contains only ExtrusionEntityCollection objects)
     [[nodiscard]] const ExtrusionEntityCollection&  fills() const { return m_fills; }
 
+    // Vector of nonplanar_surfaces which are homed in this layer
+    [[nodiscard]] const NonplanarSurfaces&          nonplanar_surfaces() const { return m_nonplanar_surfaces; }
+    
     Flow    flow(FlowRole role) const;
     Flow    flow(FlowRole role, double layer_height) const;
     Flow    bridging_flow(FlowRole role, bool force_thick_bridges = false) const;
@@ -167,6 +171,20 @@ public:
     // Is there any valid extrusion assigned to this LayerRegion?
     bool    has_extrusions() const { return ! this->perimeters().empty() || ! this->fills().empty(); }
 
+    //append a new nonplanar surface to the list skip if already in list
+    void append_nonplanar_surface(NonplanarSurface& surface);
+    // Projects the paths of a collection regarding the structure of a stl mesh
+    void project_nonplanar_extrusion(ExtrusionEntityCollection* collection);
+    /// Projects nonplanar surfaces downwards regarding the structure of the stl mesh.
+    void project_nonplanar_surfaces();
+    ///project a nonplanar path
+    void project_nonplanar_path(ExtrusionPath* path);
+    ///sets the z coordinates correctly for all points TODO move to generation of points
+    void correct_z_on_path(ExtrusionPath *path);
+    //
+    void remove_nonplanar_slices(SurfaceCollection topNonplanar);
+    void append_top_nonplanar_slices(SurfaceCollection topNonplanar);
+
 protected:
     friend class Layer;
     friend class PrintObject;
@@ -225,6 +243,8 @@ private:
     // (this collection contains only ExtrusionEntityCollection objects)
     ExtrusionEntityCollection   m_fills;
 
+    NonplanarSurfaces           m_nonplanar_surfaces;
+
     // collection of expolygons representing the bridged areas (thus not
     // needing support material)
 //  Polygons                    bridged;
@@ -379,9 +399,11 @@ public:
 
     void                    export_region_slices_to_svg(const char *path) const;
     void                    export_region_fill_surfaces_to_svg(const char *path) const;
+    void                    export_lslices_polygons_to_svg(const char *name) const;
     // Export to "out/LayerRegion-name-%d.svg" with an increasing index with every export.
     void                    export_region_slices_to_svg_debug(const char *name) const;
     void                    export_region_fill_surfaces_to_svg_debug(const char *name) const;
+    void                    export_lslices_polygons_to_svg_debug(const char *name) const;
 
     // Is there any valid extrusion assigned to this LayerRegion?
     virtual bool            has_extrusions() const { for (auto layerm : m_regions) if (layerm->has_extrusions()) return true; return false; }

src/libslic3r/LayerRegion.cpp

@@ -463,10 +463,16 @@ void LayerRegion::process_external_surfaces(const Layer *lower_layer, const Poly
     Surfaces    tops    = expand_merge_surfaces(m_fill_surfaces.surfaces, stTop, shells,
         RegionExpansionParameters::build(expansion_top, expansion_step, max_nr_expansion_steps), 
         sparse, expansion_params_into_sparse_infill, closing_radius);
+    Surfaces    nonplanarTops = expand_merge_surfaces(m_fill_surfaces.surfaces, stTopNonplanar, shells,
+        RegionExpansionParameters::build(expansion_top, expansion_step, max_nr_expansion_steps), 
+        sparse, expansion_params_into_sparse_infill, closing_radius);
+    Surfaces    nonplanarInternals = expand_merge_surfaces(m_fill_surfaces.surfaces, stInternalSolidNonplanar, shells,
+        RegionExpansionParameters::build(expansion_top, expansion_step, max_nr_expansion_steps), 
+        sparse, expansion_params_into_sparse_infill, closing_radius);
 
 //    m_fill_surfaces.remove_types({ stBottomBridge, stBottom, stTop, stInternal, stInternalSolid });
     m_fill_surfaces.clear();
-    reserve_more(m_fill_surfaces.surfaces, shells.size() + sparse.size() + bridges.size() + bottoms.size() + tops.size());
+    reserve_more(m_fill_surfaces.surfaces, shells.size() + sparse.size() + bridges.size() + bottoms.size() + tops.size() + nonplanarTops.size() + nonplanarInternals.size());
     {
         Surface solid_templ(stInternalSolid, {});
         solid_templ.thickness = layer_thickness;
@@ -480,6 +486,8 @@ void LayerRegion::process_external_surfaces(const Layer *lower_layer, const Poly
     m_fill_surfaces.append(std::move(bridges.surfaces));
     m_fill_surfaces.append(std::move(bottoms));
     m_fill_surfaces.append(std::move(tops));
+    m_fill_surfaces.append(std::move(nonplanarTops));
+    m_fill_surfaces.append(std::move(nonplanarInternals));
 
 #ifdef SLIC3R_DEBUG_SLICE_PROCESSING
     export_region_fill_surfaces_to_svg_debug("4_process_external_surfaces-final");
@@ -876,7 +884,7 @@ void LayerRegion::export_region_slices_to_svg_debug(const char *name) const
 {
     static std::map<std::string, size_t> idx_map;
     size_t &idx = idx_map[name];
-    this->export_region_slices_to_svg(debug_out_path("LayerRegion-slices-%s-%d.svg", name, idx ++).c_str());
+    this->export_region_slices_to_svg(debug_out_path("LayerRegion-%d-slices-%s-%d.svg", layer()->id(), name, idx ++).c_str());
 }
 
 void LayerRegion::export_region_fill_surfaces_to_svg(const char *path) const
@@ -903,7 +911,246 @@ void LayerRegion::export_region_fill_surfaces_to_svg_debug(const char *name) con
 {
     static std::map<std::string, size_t> idx_map;
     size_t &idx = idx_map[name];
-    this->export_region_fill_surfaces_to_svg(debug_out_path("LayerRegion-fill_surfaces-%s-%d.svg", name, idx ++).c_str());
+    this->export_region_fill_surfaces_to_svg(debug_out_path("LayerRegion-%d-fill_surfaces-%s-%d.svg", layer()->id(), name, idx ++).c_str());
+}
+
+void
+LayerRegion::append_nonplanar_surface(NonplanarSurface& surface)
+{
+    for(auto & s : m_nonplanar_surfaces){
+        if (s == surface){
+            return;
+        }    
+    }
+    m_nonplanar_surfaces.push_back(surface);
+}
+
+void
+LayerRegion::project_nonplanar_extrusion(ExtrusionEntityCollection *collection)
+{
+    for (auto& entity : collection->entities) {
+        if (ExtrusionLoop* loop = dynamic_cast<ExtrusionLoop*>(entity)) {
+            BOOST_LOG_TRIVIAL(trace) << "Projecting extrusion loop with " << loop->paths.size() << " paths";
+
+            for(auto& path : loop->paths) {
+                project_nonplanar_path(&path);
+                correct_z_on_path(&path);
+            }
+
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+            {
+                static int iRun = 0;
+                export_to_svg(debug_out_path("Layer-%d_project_extrusion_loop-%u-after.svg", layer()->id(), iRun ++).c_str(), 
+                    loop->as_polyline(), get_extents(this->slices().surfaces), scale_(0.1f));
+            }
+#endif
+        } else if (ExtrusionMultiPath* multipath = dynamic_cast<ExtrusionMultiPath*>(entity)) {
+            BOOST_LOG_TRIVIAL(trace) << "Projecting extrusion multipath with " << multipath->paths.size() << " paths";
+
+            for (auto& path : multipath->paths) {
+                project_nonplanar_path(&path);
+                correct_z_on_path(&path);
+            }
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+            {
+                static int iRun = 0;
+                export_to_svg(debug_out_path("Layer-%d_project_extrusion_multipath-%u-after.svg", layer()->id(), iRun ++).c_str(), 
+                    multipath->as_polyline(), get_extents(this->slices().surfaces), scale_(0.1f));
+            }
+#endif
+        } else if (ExtrusionPath* path = dynamic_cast<ExtrusionPath*>(entity)) {
+            BOOST_LOG_TRIVIAL(trace) << "Projecting 1 extrusion path";
+
+            project_nonplanar_path(path);
+            correct_z_on_path(path);
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+            {
+                static int iRun = 0;
+                export_to_svg(debug_out_path("Layer-%d_project_extrusion_path-%u-after.svg", layer()->id(), iRun ++).c_str(), 
+                    path->as_polyline(), get_extents(this->slices().surfaces), scale_(0.1f));
+            }
+#endif
+        } else {
+            BOOST_LOG_TRIVIAL(trace) << "Unknown entity class " << typeid(entity).name();
+            assert(false);
+        }
+    }
+}
+
+void
+LayerRegion::project_nonplanar_surfaces()
+{
+    // skip if there are no nonplanar_surfaces on this LayerRegion
+    if (m_nonplanar_surfaces.size() == 0) {
+        return;
+    }
+
+    BOOST_LOG_TRIVIAL(trace) << "Projecting " << m_nonplanar_surfaces.size() << " nonplanar surfaces for region " << 
+        region().print_region_id() << " and layer " << layer()->id() << " (z = " << layer()->print_z << ")";
+
+    // for all perimeters do path projection
+    BOOST_LOG_TRIVIAL(trace) << "Projecting " << m_perimeters.size() << " nonplanar perimeters";
+    for (auto& col : m_perimeters.entities) {
+        ExtrusionEntityCollection* collection = dynamic_cast<ExtrusionEntityCollection*>(col);
+        this->project_nonplanar_extrusion(collection);
+    }
+
+    // and all fill paths do path projection
+    BOOST_LOG_TRIVIAL(trace) << "Projecting " << m_fills.size() << " nonplanar fills";
+    for (auto& col : m_fills.entities) {
+        ExtrusionEntityCollection* collection = dynamic_cast<ExtrusionEntityCollection*>(col);
+        this->project_nonplanar_extrusion(collection);
+    }
+}
+
+//Sorting functions for soring of paths
+bool
+greaterX(const Vec3d &a, const Vec3d &b)
+{
+   return (a.x() < b.x());
+}
+
+bool
+smallerX(const Vec3d &a, const Vec3d &b)
+{
+   return (a.x() > b.x());
+}
+
+bool
+greaterY(const Vec3d &a, const Vec3d &b)
+{
+   return (a.y() < b.y());
+}
+
+bool
+smallerY(const Vec3d &a, const Vec3d &b)
+{
+   return (a.y() > b.y());
+}
+
+void
+LayerRegion::project_nonplanar_path(ExtrusionPath *path)
+{
+    //First check all points and project them regarding the triangle mesh
+    for (Point& point : path->polyline.points) {
+        for (auto& surface : m_nonplanar_surfaces) {
+            float distance_to_top = surface.stats.max.z - this->layer()->print_z;
+            for(auto& facet : surface.mesh) {
+                // skip if point is outside of the bounding box of the triangle
+                if (unscale(point).x() < std::min({facet.second.vertex[0].x, facet.second.vertex[1].x, facet.second.vertex[2].x}) ||
+                    unscale(point).x() > std::max({facet.second.vertex[0].x, facet.second.vertex[1].x, facet.second.vertex[2].x}) ||
+                    unscale(point).y() < std::min({facet.second.vertex[0].y, facet.second.vertex[1].y, facet.second.vertex[2].y}) ||
+                    unscale(point).y() > std::max({facet.second.vertex[0].y, facet.second.vertex[1].y, facet.second.vertex[2].y}))
+                {
+                    continue;
+                }
+
+                //check if point is inside of Triangle
+                if (Slic3r::Geometry::Point_in_triangle(
+                    Vec2f(unscale(point).x(), unscale(point).y()),
+                    Vec2f(facet.second.vertex[0].x, facet.second.vertex[0].y),
+                    Vec2f(facet.second.vertex[1].x, facet.second.vertex[1].y),
+                    Vec2f(facet.second.vertex[2].x, facet.second.vertex[2].y))
+                    && (facet.second.normal.z != 0))
+                {
+                    coord_t z = Slic3r::Geometry::Project_point_on_plane(Vec3f(facet.second.vertex[0].x,facet.second.vertex[0].y,facet.second.vertex[0].z),
+                                                             Vec3f(facet.second.normal.x,facet.second.normal.y,facet.second.normal.z),
+                                                             point);
+
+                    //Shift down when on lower layer
+                    point.nonplanar_z = z - scale_(distance_to_top);
+                    //break;
+                }
+            }
+        }
+    }
+
+    // Then check all line intersections, cut line on intersection and project new point
+    std::vector<Vec3crd>::size_type size = path->polyline.points.size();
+    for (std::vector<Vec3crd>::size_type i = 0; i < size-1; ++i)
+    {
+        Pointf3s intersections;
+        // check against every facet if lines intersect
+        for (auto& surface : m_nonplanar_surfaces) {
+            float distance_to_top = surface.stats.max.z - this->layer()->print_z;
+            for(auto& facet : surface.mesh) {
+                for(int j= 0; j < 3; j++) {
+                    // TODO precheck for faster computation
+                    Vec3d p1 = Vec3d(scale_(facet.second.vertex[j].x), scale_(facet.second.vertex[j].y), scale_(facet.second.vertex[j].z));
+                    Vec3d p2 = Vec3d(scale_(facet.second.vertex[(j+1) % 3].x), scale_(facet.second.vertex[(j+1) % 3].y), scale_(facet.second.vertex[(j+1) % 3].z));
+                    Vec3d* p = Slic3r::Geometry::Line_intersection(p1, p2, path->polyline.points[i], path->polyline.points[i+1]);
+
+                    if (p) {
+                        // add distance to top for every added point
+                        p->z() = p->z() - scale_(distance_to_top);
+                        intersections.push_back(*p);
+                    }
+                }
+            }
+        }
+
+        // Stop if no intersections are found
+        if (intersections.size() == 0) continue;
+
+        // sort found intersectons if there are more than 1
+        if ( intersections.size() > 1 ){
+            if (abs(path->polyline.points[i+1].x() - path->polyline.points[i].x()) >= abs(path->polyline.points[i+1].y() - path->polyline.points[i].y()) ) {
+                // sort by X
+                if(path->polyline.points[i].x() < path->polyline.points[i+1].x()) {
+                    std::sort(intersections.begin(), intersections.end(), smallerX);
+                }else {
+                    std::sort(intersections.begin(), intersections.end(), greaterX);
+                }
+            } else {
+                // sort by Y
+                if(path->polyline.points[i].y() < path->polyline.points[i+1].y()) {
+                    std::sort(intersections.begin(), intersections.end(), smallerY);
+                }else {
+                    std::sort(intersections.begin(), intersections.end(), greaterY);
+                }
+            }
+        }
+
+        // remove duplicates
+        Pointf3s::iterator point = intersections.begin();
+        while (point != intersections.end()-1) {
+            bool delete_point = false;
+            Pointf3s::iterator point2 = point;
+            ++point2;
+            //compare with next point if they are the same, delete current point
+            if ((*point).x() == (*point2).x() && (*point).y() == (*point2).y()) {
+                    //remove duplicate point
+                    delete_point = true;
+                    point = intersections.erase(point);
+            }
+            //continue loop when no point is removed. Otherwise the new point is set while deleting the old one.
+            if (!delete_point) {
+                ++point;
+            }
+        }
+
+        //insert new points into array
+        for (Vec3d p : intersections)
+        {
+            Point *pt = new Point(p.x(), p.y());
+            pt->nonplanar_z = p.z();
+            path->polyline.points.insert(path->polyline.points.begin()+i+1, *pt);
+        }
+
+        //modifiy array boundary
+        i = i + intersections.size();
+        size = size + intersections.size();
+    }
+}
+
+void
+LayerRegion::correct_z_on_path(ExtrusionPath *path)
+{
+    for (Point& point : path->polyline.points) {
+        if(point.nonplanar_z == -1) {
+            point.nonplanar_z = scale_(this->layer()->print_z);
+        }
+    }
 }
 
 }

src/libslic3r/MultiPoint.cpp

@@ -103,8 +103,28 @@ bool MultiPoint::remove_duplicate_points()
     return false;
 }
 
+bool
+MultiPoint::needs_zmove(const Points &pts)
+{
+    coord_t z = -1;
+    //check if any point in travel is below the layer z
+    for (Point p : pts)
+    {
+        if(z == -1) {
+            z = p.nonplanar_z;
+        }
+        else if ((p.nonplanar_z != -1) && (p.nonplanar_z != z))
+            return true;
+    }
+
+    return false;
+}
+
 Points MultiPoint::douglas_peucker(const Points &pts, const double tolerance)
 {
+    if(MultiPoint::needs_zmove(pts))
+        return pts;
+
     Points result_pts;
 	auto tolerance_sq = int64_t(sqr(tolerance));
     if (! pts.empty()) {

src/libslic3r/MultiPoint.hpp

@@ -81,6 +81,7 @@ public:
         }
     }
 
+    static bool needs_zmove(const Points &pts);
     static Points douglas_peucker(const Points &points, const double tolerance);
     static Points visivalingam(const Points& pts, const double& tolerance);
 

src/libslic3r/NonplanarFacet.cpp

@@ -0,0 +1,72 @@
+#include "NonplanarFacet.hpp"
+
+namespace Slic3r {
+
+void
+NonplanarFacet::calculate_stats() {
+    //calculate min and max values
+    this->stats.min.x = this->vertex[0].x;
+    this->stats.min.y = this->vertex[0].y;
+    this->stats.min.z = this->vertex[0].z;
+    this->stats.max.x = this->vertex[0].x;
+    this->stats.max.y = this->vertex[0].y;
+    this->stats.max.z = this->vertex[0].z;
+    for(int j = 1; j < 3; j++) {
+        this->stats.min.x = std::min(this->stats.min.x, this->vertex[j].x);
+        this->stats.min.y = std::min(this->stats.min.y, this->vertex[j].y);
+        this->stats.min.z = std::min(this->stats.min.z, this->vertex[j].z);
+        this->stats.max.x = std::max(this->stats.max.x, this->vertex[j].x);
+        this->stats.max.y = std::max(this->stats.max.y, this->vertex[j].y);
+        this->stats.max.z = std::max(this->stats.max.z, this->vertex[j].z);
+    }
+}
+
+void
+NonplanarFacet::translate(float x, float y, float z)
+{
+    //translate facet
+    for(int j = 0; j < 3; j++) {
+      this->vertex[j].x += x;
+      this->vertex[j].y += y;
+      this->vertex[j].z += z;
+    }
+
+    //translate min and max values
+    this->stats.min.x += x;
+    this->stats.min.y += y;
+    this->stats.min.z += z;
+    this->stats.max.x += x;
+    this->stats.max.y += y;
+    this->stats.max.z += z;
+}
+
+void
+NonplanarFacet::scale(float versor[3])
+{
+    //scale facet
+    for(int j = 0; j < 3; j++) {
+        this->vertex[j].x *= versor[0];
+        this->vertex[j].y *= versor[1];
+        this->vertex[j].z *= versor[2];
+    }
+
+    //scale min and max values
+    this->stats.min.x *= versor[0];
+    this->stats.min.y *= versor[1];
+    this->stats.min.z *= versor[2];
+    this->stats.max.x *= versor[0];
+    this->stats.max.y *= versor[1];
+    this->stats.max.z *= versor[2];
+}
+
+float
+NonplanarFacet::calculate_surface_area()
+{
+    return Slic3r::Geometry::triangle_surface(
+        Point(this->vertex[0].x, this->vertex[0].y), 
+        Point(this->vertex[1].x, this->vertex[1].y), 
+        Point(this->vertex[2].x, this->vertex[2].y)
+    );
+}
+
+}

src/libslic3r/NonplanarFacet.hpp

@@ -0,0 +1,39 @@
+#ifndef slic3r_NonplanarFacet_hpp_
+#define slic3r_NonplanarFacet_hpp_
+
+#include "libslic3r.h"
+#include "Geometry.hpp"
+
+namespace Slic3r {
+
+typedef struct {
+  float x;
+  float y;
+  float z;
+} facet_vertex;
+
+typedef struct {
+  facet_vertex    max;
+  facet_vertex    min;
+} facet_stats;
+
+class NonplanarFacet
+{
+    public:
+    facet_vertex vertex[3];
+    facet_vertex normal;
+    int neighbor[3];
+    facet_stats stats;
+    bool marked = false;
+
+    NonplanarFacet() {};
+    ~NonplanarFacet() {};
+    void calculate_stats();
+    void translate(float x, float y, float z);
+    void scale(float versor[3]);
+    float calculate_surface_area();
+
+};
+};
+
+#endif

src/libslic3r/NonplanarSurface.cpp

@@ -0,0 +1,240 @@
+#include "NonplanarSurface.hpp"
+
+namespace Slic3r {
+
+NonplanarSurface::NonplanarSurface(std::map<int, NonplanarFacet> &_mesh)
+{
+    this->mesh = _mesh;
+    this->calculate_stats();
+}
+
+bool 
+NonplanarSurface::operator==(const NonplanarSurface& other) const {
+   return (stats.min.x == other.stats.min.x &&
+           stats.min.y == other.stats.min.y &&
+           stats.min.z == other.stats.min.z &&
+           stats.max.x == other.stats.max.x &&
+           stats.max.y == other.stats.max.y &&
+           stats.max.z == other.stats.max.z);
+}
+
+void
+NonplanarSurface::calculate_stats()
+{
+    //calculate min and max values
+    this->stats.min.x = 10000000;
+    this->stats.min.y = 10000000;
+    this->stats.min.z = 10000000;
+    this->stats.max.x = -10000000;
+    this->stats.max.y = -10000000;
+    this->stats.max.z = -10000000;
+    for(auto& facet : this->mesh) {
+        this->stats.min.x = std::min(this->stats.min.x, facet.second.stats.min.x);
+        this->stats.min.y = std::min(this->stats.min.y, facet.second.stats.min.y);
+        this->stats.min.z = std::min(this->stats.min.z, facet.second.stats.min.z);
+        this->stats.max.x = std::max(this->stats.max.x, facet.second.stats.max.x);
+        this->stats.max.y = std::max(this->stats.max.y, facet.second.stats.max.y);
+        this->stats.max.z = std::max(this->stats.max.z, facet.second.stats.max.z);
+    }
+}
+
+void
+NonplanarSurface::translate(float x, float y, float z)
+{
+    //translate all facets
+    for(auto& facet : this->mesh) {
+        facet.second.translate(x, y, z);
+    }
+
+    //translate min and max values
+    this->stats.min.x += x;
+    this->stats.min.y += y;
+    this->stats.min.z += z;
+    this->stats.max.x += x;
+    this->stats.max.y += y;
+    this->stats.max.z += z;
+}
+
+void
+NonplanarSurface::scale(float factor)
+{
+    float versor[3];
+    versor[0] = factor;
+    versor[1] = factor;
+    versor[2] = factor;
+    this->scale(versor);
+}
+
+void
+NonplanarSurface::scale(float versor[3])
+{
+    //scale all facets
+    for(auto& facet : this->mesh) {
+        facet.second.scale(versor);
+    }
+
+    //scale min and max values
+    this->stats.min.x *= versor[0];
+    this->stats.min.y *= versor[1];
+    this->stats.min.z *= versor[2];
+    this->stats.max.x *= versor[0];
+    this->stats.max.y *= versor[1];
+    this->stats.max.z *= versor[2];
+}
+
+void
+NonplanarSurface::rotate_z(float angle) {
+  double radian_angle = (angle / 180.0) * 3.1415927;
+  double c = cos(radian_angle);
+  double s = sin(radian_angle);
+
+  for(auto& facet : this->mesh) {
+    for(int j = 0; j < 3; j++) {
+        double xold = facet.second.vertex[j].x;
+        double yold = facet.second.vertex[j].y;
+        facet.second.vertex[j].x = c * xold - s * yold;
+        facet.second.vertex[j].y = s * xold + c * yold;
+    }
+    facet.second.calculate_stats();
+  }
+
+  this->calculate_stats();
+}
+
+void
+NonplanarSurface::debug_output()
+{
+    std::cout << "Facets(" << this->mesh.size() << "): (min:X:" << this->stats.min.x << " Y:" << this->stats.min.y << " Z:" << this->stats.min.z <<
+                           " max:X:" << this->stats.max.x << " Y:" << this->stats.max.y << " Z:" << this->stats.max.z << ")" << 
+                           "Height " << this->stats.max.z - this->stats.min.z << std::endl;
+    for(auto& facet : this->mesh) {
+        std::cout << "triangle: (" << facet.first << ")(" << facet.second.marked << ") ";
+        std::cout << " (" << (180*std::acos(facet.second.normal.z))/3.14159265 << "°)";
+
+        std::cout << " | V0:";
+        std::cout << " X:"<< facet.second.vertex[0].x;
+        std::cout << " Y:"<< facet.second.vertex[0].y;
+        std::cout << " Z:"<< facet.second.vertex[0].z;
+
+        std::cout << " | V1:";
+        std::cout << " X:"<< facet.second.vertex[1].x;
+        std::cout << " Y:"<< facet.second.vertex[1].y;
+        std::cout << " Z:"<< facet.second.vertex[1].z;
+
+        std::cout << " | V2:";
+        std::cout << " X:"<< facet.second.vertex[2].x;
+        std::cout << " Y:"<< facet.second.vertex[2].y;
+        std::cout << " Z:"<< facet.second.vertex[2].z;
+
+        std::cout << " | Normal:";
+        std::cout << " X:"<< facet.second.normal.x;
+        std::cout << " Y:"<< facet.second.normal.y;
+        std::cout << " Z:"<< facet.second.normal.z;
+
+        //TODO check if neighbors exist
+        // stl_neighbors* neighbors = mesh.stl.neighbors_start + facet.first;
+        std::cout << " | Neighbors:";
+        std::cout << " 0:"<< facet.second.neighbor[0];
+        std::cout << " 1:"<< facet.second.neighbor[1];
+        std::cout << " 2:"<< facet.second.neighbor[2];
+        std::cout << std::endl;
+    }
+}
+
+NonplanarSurfaces
+NonplanarSurface::group_surfaces()
+{
+    std::pair<int, NonplanarFacet> begin = *this->mesh.begin();
+    this->mark_neighbor_surfaces(begin.first);
+    NonplanarSurface newSurface;
+    for (std::map<int, NonplanarFacet>::iterator it=this->mesh.begin(); it!=this->mesh.end();) {
+        if((*it).second.marked == false) {
+            newSurface.mesh[(*it).first] = (*it).second;
+            it = this->mesh.erase(it);
+        }
+        else {
+            ++it;
+        }
+    }
+    this->calculate_stats();
+    if (newSurface.mesh.size() == 0) {
+        //return only this
+        NonplanarSurfaces nonplanar_surfaces;
+        nonplanar_surfaces.push_back(*this);
+        return nonplanar_surfaces;
+    } 
+    else {
+        //return union of this and recursion
+        NonplanarSurfaces nonplanar_surfaces = newSurface.group_surfaces();
+        nonplanar_surfaces.push_back(*this);
+        return nonplanar_surfaces;
+    }
+}
+
+void
+NonplanarSurface::mark_neighbor_surfaces(int id)
+{
+    //if already marked return
+    if(this->mesh.find(id) == this->mesh.end() || this->mesh[id].marked == true) return;
+    //mark this facet
+    this->mesh[id].marked = true;
+    //mark all neighbors
+    for(int j = 0; j < 3; j++) {
+        this->mark_neighbor_surfaces(this->mesh[id].neighbor[j]);
+    }
+}
+
+bool
+NonplanarSurface::check_max_printing_height(float height) 
+{
+    if ((this->stats.max.z - this->stats.min.z) > height ) {
+        std::cout << "Surface removed: printheight too heigh (" << (this->stats.max.z - this->stats.min.z) << " mm)" << '\n';
+        return true;
+    } else {
+        return false;
+    }
+}
+
+bool
+NonplanarSurface::check_surface_area()
+{
+    //calculate surface area of nonplanar surface.
+    float area = 0.0f;
+    for(auto& facet : this->mesh) {
+        area += facet.second.calculate_surface_area();
+    }
+    if (area < 20.0f) {
+        std::cout << "Surface removed: area too small (" << area << " mm²)" << '\n';
+        return true;
+    } else {
+        return false;
+    }
+}
+
+void
+NonplanarSurface::check_printable_surfaces(float max_angle)
+{
+    //TODO do something
+}
+
+/* this will return scaled ExPolygons */
+ExPolygons
+NonplanarSurface::horizontal_projection() const
+{
+    Polygons pp;
+    pp.reserve(this->mesh.size());
+    for(auto& facet : this->mesh) {
+        Polygon p;
+        p.points.resize(3);
+        p.points[0] = Point(scale_(facet.second.vertex[0].x), scale_(facet.second.vertex[0].y));
+        p.points[1] = Point(scale_(facet.second.vertex[1].x), scale_(facet.second.vertex[1].y));
+        p.points[2] = Point(scale_(facet.second.vertex[2].x), scale_(facet.second.vertex[2].y));
+        p.make_counter_clockwise();  // do this after scaling, as winding order might change while doing that
+        pp.push_back(p);
+    }
+
+    // the offset factor was tuned using groovemount.stl
+    return union_ex(offset(pp, scale_(0.01)));
+}
+
+}

src/libslic3r/NonplanarSurface.hpp

@@ -0,0 +1,54 @@
+#ifndef slic3r_NonplanarSurface_hpp_
+#define slic3r_NonplanarSurface_hpp_
+
+#include "libslic3r.h"
+#include "NonplanarFacet.hpp"
+#include "Point.hpp"
+#include "Polygon.hpp"
+#include "ExPolygon.hpp"
+#include "Geometry.hpp"
+#include "ClipperUtils.hpp"
+
+namespace Slic3r {
+
+typedef struct {
+  float x;
+  float y;
+  float z;
+} mesh_vertex;
+
+typedef struct {
+  mesh_vertex    max;
+  mesh_vertex    min;
+} mesh_stats;
+
+class NonplanarSurface;
+
+typedef std::vector<NonplanarSurface> NonplanarSurfaces;
+
+class NonplanarSurface
+{
+    public:
+    std::map<int, NonplanarFacet> mesh;
+    mesh_stats stats;
+    NonplanarSurface() {};
+    ~NonplanarSurface() {};
+    NonplanarSurface(std::map<int, NonplanarFacet> &_mesh);
+    bool operator==(const NonplanarSurface& other) const;
+    void calculate_stats();
+    void translate(float x, float y, float z);
+    void scale(float factor);
+    void scale(float versor[3]);
+    void rotate_z(float angle);
+    void debug_output();
+    NonplanarSurfaces group_surfaces();
+    void mark_neighbor_surfaces(int id);
+    bool check_max_printing_height(float height);
+    void check_printable_surfaces(float max_angle);
+    bool check_surface_area();
+    ExPolygons horizontal_projection() const;
+
+};
+};
+
+#endif

src/libslic3r/Point.hpp

@@ -159,11 +159,14 @@ class Point : public Vec2crd
 public:
     using coord_type = coord_t;
 
+    coord_t nonplanar_z { -1 };
+
     Point() : Vec2crd(0, 0) {}
     Point(int32_t x, int32_t y) : Vec2crd(coord_t(x), coord_t(y)) {}
     Point(int64_t x, int64_t y) : Vec2crd(coord_t(x), coord_t(y)) {}
     Point(double x, double y) : Vec2crd(coord_t(std::round(x)), coord_t(std::round(y))) {}
     Point(const Point &rhs) { *this = rhs; }
+    Point(Vec3crd &p) : Vec2crd(p.x(), p.y()) {}
 	explicit Point(const Vec2d& rhs) : Vec2crd(coord_t(std::round(rhs.x())), coord_t(std::round(rhs.y()))) {}
 	// This constructor allows you to construct Point from Eigen expressions
     template<typename OtherDerived>

src/libslic3r/Polygon.cpp

@@ -402,7 +402,7 @@ bool has_duplicate_points(const Polygons &polys)
 {
 #if 1
     // Check globally.
-#if 0
+#if 1
     // Detect duplicates by sorting with quicksort. It is quite fast, but ankerl::unordered_dense is around 1/4 faster.
     Points allpts;
     allpts.reserve(count_points(polys));

src/libslic3r/Polyline.cpp

@@ -4,6 +4,7 @@
 #include "ExPolygon.hpp"
 #include "Line.hpp"
 #include "Polygon.hpp"
+#include "SVG.hpp"
 #include <iostream>
 #include <utility>
 
@@ -332,4 +333,29 @@ Lines3 Polyline3::lines() const
     return lines;
 }
 
+bool export_to_svg(const char *path, const Polyline &polyline, BoundingBox bbox, const float stroke_width)
+{
+    SVG svg(path, bbox);
+    svg.draw(polyline, "black", stroke_width);
+    svg.Close();
+    return true;
+}
+
+bool export_to_svg(const char *path, const Polylines &polylines, BoundingBox bbox, const float stroke_width)
+{
+    SVG svg(path, bbox);
+    svg.draw(polylines, "black", stroke_width);
+    svg.Close();
+    return true;
+}
+
+bool export_to_svg(const char *path, const ThickPolylines &polylines, BoundingBox bbox, const float stroke_width)
+{
+    SVG svg(path, bbox);
+    svg.draw(polylines, "black", stroke_width);
+    svg.Close();
+    return true;
+}
+
+
 }

src/libslic3r/Polyline.hpp

@@ -234,6 +234,10 @@ public:
 
 typedef std::vector<Polyline3> Polylines3;
 
+extern bool export_to_svg(const char *path, const Polyline &polyline, BoundingBox bbox, const float stroke_width = 1.f);
+extern bool export_to_svg(const char *path, const Polylines &polylines, BoundingBox bbox, const float stroke_width = 1.f);
+extern bool export_to_svg(const char *path, const ThickPolylines &polylines, BoundingBox bbox, const float stroke_width = 1.f);
+
 }
 
 #endif

src/libslic3r/Preset.cpp

@@ -432,6 +432,7 @@ static std::vector<std::string> s_Preset_print_options {
     "ironing", "ironing_type", "ironing_flowrate", "ironing_speed", "ironing_spacing",
     "max_print_speed", "max_volumetric_speed", "avoid_crossing_perimeters_max_detour",
     "fuzzy_skin", "fuzzy_skin_thickness", "fuzzy_skin_point_dist",
+    "use_nonplanar_layers", "nonplanar_layers_angle", "nonplanar_layers_height",
     "max_volumetric_extrusion_rate_slope_positive", "max_volumetric_extrusion_rate_slope_negative",
     "perimeter_speed", "small_perimeter_speed", "external_perimeter_speed", "infill_speed", "solid_infill_speed",
     "enable_dynamic_overhang_speeds", "overhang_speed_0", "overhang_speed_1", "overhang_speed_2", "overhang_speed_3",

src/libslic3r/Print.hpp

@@ -17,6 +17,8 @@
 #include "GCode/ThumbnailData.hpp"
 #include "GCode/GCodeProcessor.hpp"
 #include "MultiMaterialSegmentation.hpp"
+#include "NonplanarSurface.hpp"
+#include "NonplanarFacet.hpp"
 
 #include "libslic3r.h"
 
@@ -67,7 +69,9 @@ enum PrintStep : unsigned int {
 
 enum PrintObjectStep : unsigned int {
     posSlice, posPerimeters, posPrepareInfill,
-    posInfill, posIroning, posSupportSpotsSearch, posSupportMaterial, posEstimateCurledExtrusions, posCount,
+    posInfill, posIroning, posSupportSpotsSearch, 
+    posSupportMaterial, posNonplanarProjection, posEstimateCurledExtrusions, 
+    posCount,
 };
 
 // A PrintRegion object represents a group of volumes to print
@@ -264,6 +268,8 @@ public:
     coord_t 				     height() const         { return m_size.z(); }
     // Centering offset of the sliced mesh from the scaled and rotated mesh of the model.
     const Point& 			     center_offset() const  { return m_center_offset; }
+    // 
+    NonplanarSurfaces            nonplanar_surfaces()   { return m_nonplanar_surfaces; }
 
     bool                         has_brim() const       {
         return this->config().brim_type != btNoBrim
@@ -378,8 +384,16 @@ private:
     void estimate_curled_extrusions();
 
     void slice_volumes();
+    void make_slices();
+    void lslices_were_updated();
     // Has any support (not counting the raft).
     void detect_surfaces_type();
+    void merge_nonplanar_surfaces();
+    void debug_svg_print();
+    bool check_nonplanar_collisions(NonplanarSurface &surface);
+    void project_nonplanar_surfaces();
+    void find_nonplanar_surfaces();
+    void detect_nonplanar_surfaces();
     void process_external_surfaces();
     void discover_vertical_shells();
     void bridge_over_infill();
@@ -414,6 +428,8 @@ private:
     // so that next call to make_perimeters() performs a union() before computing loops
     bool                    				m_typed_slices = false;
 
+    NonplanarSurfaces                       m_nonplanar_surfaces;
+
     std::pair<FillAdaptive::OctreePtr, FillAdaptive::OctreePtr> m_adaptive_fill_octrees;
     FillLightning::GeneratorPtr m_lightning_generator;
 };

src/libslic3r/PrintConfig.cpp

@@ -1369,6 +1369,33 @@ void PrintConfigDef::init_fff_params()
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionFloat(0.8));
 
+
+    def = this->add("use_nonplanar_layers", coBool);
+    def->label = L("Use nonplanar layers");
+    def->category = L("Nonplanar layers");
+    def->tooltip = L("Generate nonplanar layers on top of the object");
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionBool(false));
+
+    def = this->add("nonplanar_layers_angle", coFloat);
+    def->label = L("Maximum nonplanar angle");
+    def->category = L("Nonplanar layers");
+    def->tooltip = L("The maximum angle the printer can print without collisions.");
+    def->sidetext = L("°");
+    def->min = 0;
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionFloat(10.0));
+
+    def = this->add("nonplanar_layers_height", coFloat);
+    def->label = L("Maximum nonplanar height");
+    def->category = L("Nonplanar layers");
+    def->tooltip = L("The maximum height the printer can print without collisions.");
+    def->sidetext = L("mm");
+    def->min = 0;
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionFloat(10.0));
+
+
     def = this->add("gap_fill_enabled", coBool);
     def->label = L("Fill gaps");
     def->category = L("Layers and Perimeters");

src/libslic3r/PrintConfig.hpp

@@ -562,6 +562,10 @@ PRINT_CONFIG_CLASS_DEFINE(
     ((ConfigOptionBool,                thick_bridges))
     ((ConfigOptionFloat,               xy_size_compensation))
     ((ConfigOptionBool,                wipe_into_objects))
+
+    ((ConfigOptionBool,                 use_nonplanar_layers))
+    ((ConfigOptionFloat,                nonplanar_layers_angle))
+    ((ConfigOptionFloat,                nonplanar_layers_height))
 )
 
 PRINT_CONFIG_CLASS_DEFINE(

src/libslic3r/PrintObject.cpp

@@ -33,6 +33,7 @@
 #include "TriangleSelectorWrapper.hpp"
 #include "format.hpp"
 #include "libslic3r.h"
+#include "SVG.hpp"
 
 #include <algorithm>
 #include <cmath>
@@ -53,6 +54,7 @@
 #include <utility>
 
 #include <boost/log/trivial.hpp>
+#include <boost/bind.hpp>
 
 #include <tbb/parallel_for.h>
 #include <vector>
@@ -179,6 +181,8 @@ void PrintObject::make_perimeters()
         m_typed_slices = false;
     }
 
+    this->detect_nonplanar_surfaces();
+    
     // compare each layer to the one below, and mark those slices needing
     // one additional inner perimeter, like the top of domed objects-
     
@@ -275,16 +279,17 @@ void PrintObject::prepare_infill()
 
     m_print->set_status(30, _u8L("Preparing infill"));
 
-    if (m_typed_slices) {
+    // if (m_typed_slices) {
-        // To improve robustness of detect_surfaces_type() when reslicing (working with typed slices), see GH issue #7442.
+    //     // To improve robustness of detect_surfaces_type() when reslicing (working with typed slices), see GH issue #7442.
-        // The preceding step (perimeter generator) only modifies extra_perimeters and the extra perimeters are only used by discover_vertical_shells()
+    //     // The preceding step (perimeter generator) only modifies extra_perimeters and the extra perimeters are only used by discover_vertical_shells()
-        // with more than a single region. If this step does not use Surface::extra_perimeters or Surface::extra_perimeters is always zero, it is safe
+    //     // with more than a single region. If this step does not use Surface::extra_perimeters or Surface::extra_perimeters is always zero, it is safe
-        // to reset to the untyped slices before re-runnning detect_surfaces_type().
+    //     // to reset to the untyped slices before re-runnning detect_surfaces_type().
-        for (Layer* layer : m_layers) {
+    //     for (Layer* layer : m_layers) {
-            layer->restore_untyped_slices_no_extra_perimeters();
+    //         layer->restore_untyped_slices_no_extra_perimeters();
-            m_print->throw_if_canceled();
+    //         m_print->throw_if_canceled();
-        }
+    //     }
-    }
+    //     this->detect_nonplanar_surfaces();
+    // }
 
     // This will assign a type (top/bottom/internal) to $layerm->slices.
     // Then the classifcation of $layerm->slices is transfered onto 
@@ -434,6 +439,9 @@ void PrintObject::infill()
                 }
             }
         );
+
+        this->project_nonplanar_surfaces();
+
         m_print->throw_if_canceled();
         BOOST_LOG_TRIVIAL(debug) << "Filling layers in parallel - end";
         /*  we could free memory now, but this would make this step not idempotent
@@ -792,6 +800,13 @@ bool PrintObject::invalidate_state_by_config_options(
             	steps.emplace_back(posInfill);
 	            steps.emplace_back(posSupportMaterial);
 	        }
+        } else if (
+               opt_key == "use_nonplanar_layers"
+            || opt_key == "nonplanar_layers_angle"
+            || opt_key == "nonplanar_layers_height") {
+            // steps.emplace_back(posPerimeters);
+            // steps.emplace_back(posInfill);
+            steps.emplace_back(posSlice);
         } else if (
             opt_key == "perimeter_generator"
             || opt_key == "wall_transition_length"
@@ -899,6 +914,8 @@ void PrintObject::cleanup()
 // stBottomBridge - Part of a region, which is not fully supported, but it hangs in the air, or it hangs losely on a support or a raft.
 // stBottom       - Part of a region, which is not supported by the same region, but it is supported either by another region, or by a soluble interface layer.
 // stInternal     - Part of a region, which is supported by the same region type.
+// stTopNonplanar - 
+// stInternalSolidNonplanar - 
 // If a part of a region is of stBottom and stTop, the stBottom wins.
 void PrintObject::detect_surfaces_type()
 {
@@ -952,6 +969,22 @@ void PrintObject::detect_surfaces_type()
                     // collapse very narrow parts (using the safety offset in the diff is not enough)
                     float        offset = layerm->flow(frExternalPerimeter).scaled_width() / 10.f;
 
+                    //Find mark nonplanar surfaces
+                    Surfaces nonplanar_surfaces;
+                    for(auto& surface : layerm->nonplanar_surfaces()) {
+                        surfaces_append(
+                            nonplanar_surfaces,
+                            intersection_ex(surface.horizontal_projection(), union_ex(layerm->slices().surfaces)),
+                            (surface.stats.max.z <= layer->slice_z + layer->height ? stTopNonplanar : stInternalSolidNonplanar)
+                        );
+                        BOOST_LOG_TRIVIAL(trace) << "Detecting solid surfaces - layer " << (idx_layer+1) << "/" << m_layers.size() << " is " << 
+                            (surface.stats.max.z <= layer->slice_z + layer->height ? "top nonplanar" : "internal nonplanar") <<
+                            ", surface max z=" << surface.stats.max.z << ", slice_z=" << layer->slice_z << ", layer height=" << layer->height;
+                    }
+
+                    //remove non planar surfaces form all surfaces to get planar surfaces
+                    ExPolygons planar_surfaces = diff_ex(layerm->slices().surfaces, nonplanar_surfaces, ApplySafetyOffset::Yes);
+
                     // find top surfaces (difference between current surfaces
                     // of current layer and upper one)
                     Surfaces top;
@@ -959,13 +992,11 @@ void PrintObject::detect_surfaces_type()
                         ExPolygons upper_slices = interface_shells ? 
                             diff_ex(layerm->slices().surfaces, upper_layer->m_regions[region_id]->slices().surfaces, ApplySafetyOffset::Yes) :
                             diff_ex(layerm->slices().surfaces, upper_layer->lslices, ApplySafetyOffset::Yes);
-                        surfaces_append(top, opening_ex(upper_slices, offset), stTop);
+                        surfaces_append(top, diff_ex(opening_ex(upper_slices, offset), nonplanar_surfaces, ApplySafetyOffset::Yes), stTop);
                     } else {
                         // if no upper layer, all surfaces of this one are solid
                         // we clone surfaces because we're going to clear the slices collection
-                        top = layerm->slices().surfaces;
+                        surfaces_append(top, union_ex(planar_surfaces), stTop);
-                        for (Surface &surface : top)
-                            surface.surface_type = stTop;
                     }
                     
                     // Find bottom surfaces (difference between current surfaces of current layer and lower one).
@@ -984,7 +1015,11 @@ void PrintObject::detect_surfaces_type()
                         surfaces_append(
                             bottom,
                             opening_ex(
+                                diff_ex(
                                     diff_ex(layerm->slices().surfaces, lower_layer->lslices, ApplySafetyOffset::Yes),
+                                    nonplanar_surfaces,
+                                    ApplySafetyOffset::Yes
+                                ),
                                 offset),
                             surface_type_bottom_other);
                         // if user requested internal shells, we need to identify surfaces
@@ -995,10 +1030,13 @@ void PrintObject::detect_surfaces_type()
                             surfaces_append(
                                 bottom,
                                 opening_ex(
+                                    diff_ex(
                                         diff_ex(
                                             intersection(layerm->slices().surfaces, lower_layer->lslices), // supported
                                             lower_layer->m_regions[region_id]->slices().surfaces,
                                             ApplySafetyOffset::Yes),
+                                        nonplanar_surfaces,
+                                        ApplySafetyOffset::Yes),
                                     offset),
                                 stBottom);
                         }
@@ -1029,6 +1067,7 @@ void PrintObject::detect_surfaces_type()
                         std::vector<std::pair<Slic3r::ExPolygons, SVG::ExPolygonAttributes>> expolygons_with_attributes;
                         expolygons_with_attributes.emplace_back(std::make_pair(union_ex(top),                             SVG::ExPolygonAttributes("green")));
                         expolygons_with_attributes.emplace_back(std::make_pair(union_ex(bottom),                          SVG::ExPolygonAttributes("brown")));
+                        expolygons_with_attributes.emplace_back(std::make_pair(union_ex(nonplanar_surfaces),              SVG::ExPolygonAttributes("red")));
                         expolygons_with_attributes.emplace_back(std::make_pair(to_expolygons(layerm->slices().surfaces),  SVG::ExPolygonAttributes("black")));
                         SVG::export_expolygons(debug_out_path("1_detect_surfaces_type_%d_region%d-layer_%f.svg", iRun ++, region_id, layer->print_z).c_str(), expolygons_with_attributes);
                     }
@@ -1045,13 +1084,15 @@ void PrintObject::detect_surfaces_type()
 
                     // find internal surfaces (difference between top/bottom surfaces and others)
                     {
-                        Polygons topbottom = to_polygons(top);
+                        Polygons solid_surfaces = to_polygons(top);
-                        polygons_append(topbottom, to_polygons(bottom));
+                        polygons_append(solid_surfaces, to_polygons(bottom));
-                        surfaces_append(surfaces_out, diff_ex(surfaces_prev, topbottom), stInternal);
+                        polygons_append(solid_surfaces, to_polygons(nonplanar_surfaces));
+                        surfaces_append(surfaces_out, diff_ex(surfaces_prev, solid_surfaces), stInternal);
                     }
 
                     surfaces_append(surfaces_out, std::move(top));
                     surfaces_append(surfaces_out, std::move(bottom));
+                    surfaces_append(surfaces_out, std::move(nonplanar_surfaces));
                     
         //            Slic3r::debugf "  layer %d has %d bottom, %d top and %d internal surfaces\n",
         //                $layerm->layer->id, scalar(@bottom), scalar(@top), scalar(@internal) if $Slic3r::debug;
@@ -1101,6 +1142,240 @@ void PrintObject::detect_surfaces_type()
     m_typed_slices = true;
 }
 
+bool
+PrintObject::check_nonplanar_collisions(NonplanarSurface &surface)
+{
+	for (size_t region_id = 0; region_id < this->num_printing_regions(); ++ region_id) {
+        Polygons collider;
+        Polygons nonplanar_polygon = to_polygons(surface.horizontal_projection());
+        //check each layer
+        for (size_t idx_layer = 0; idx_layer < m_layers.size(); ++ idx_layer) {
+            m_print->throw_if_canceled();
+            // BOOST_LOG_TRIVIAL(trace) << "Check nonplanar collisions for region " << region_id << " and layer " << layer->print_z;
+            Layer       *layer  = m_layers[idx_layer];
+            LayerRegion *layerm = layer->m_regions[region_id];
+
+            //skip if below minimum nonplanar surface
+            if (surface.stats.min.z-layer->height > layer->slice_z) continue;
+            //break if above nonplanar surface
+            if (surface.stats.max.z < layer->slice_z) break;
+
+            float angle_rad = m_config.nonplanar_layers_angle.value * 3.14159265/180.0;
+            float angle_offset = scale_(layer->height*std::sin(1.57079633-angle_rad)/std::sin(angle_rad));
+
+            //debug
+            // SVG svg("svg/collider" + std::to_string(layer->id()) + ".svg");
+            // svg.draw(layerm_slices_surfaces, "blue");
+            // svg.draw(union_ex(diff(collider,nonplanar_polygon)), "red", 0.7f);
+            // svg.draw_outline(collider);
+            // svg.arrows = false;
+            // svg.Close();
+
+            //check if current surface collides with previous collider
+            ExPolygons collisions = union_ex(intersection(layerm->slices().surfaces, diff(collider, nonplanar_polygon)));
+
+            if (!collisions.empty()){
+                double area = 0;
+                for (auto& c : collisions){
+                    area += c.area();
+                }
+
+                //collsion found abort when area > 1.0 mm²
+                if (1.0 < unscale<double>(unscale<double>(area))) {
+                    std::cout << "Surface removed: collision on layer " << layer->print_z << "mm (" << unscale<double>(unscale<double>(area)) << " mm²)" << '\n';
+                    return true;
+                }
+            }
+
+            if (layer->upper_layer != NULL) {
+                Layer* upper_layer = layer->upper_layer;
+                LayerRegion *upper_layerm = upper_layer->m_regions[region_id];
+                //merge the ofsetted surface to the collider
+                collider= offset(
+                            union_(
+                                intersection(
+                                    diff_ex(layerm->slices().surfaces, upper_layerm->slices().surfaces, ApplySafetyOffset::No),
+                                    nonplanar_polygon,
+                                    ApplySafetyOffset::No), 
+                                collider),
+                            angle_offset);
+            }
+        }
+    }
+
+    return false;
+}
+
+void
+PrintObject::detect_nonplanar_surfaces()
+{
+    //skip if not active
+    if(!m_config.use_nonplanar_layers.value) return;
+
+    bool moved_surfaces = false;
+
+    for (size_t region_id = 0; region_id < this->num_printing_regions(); ++ region_id) {
+        m_print->throw_if_canceled();
+        BOOST_LOG_TRIVIAL(trace) << "detect_nonplanar_surfaces for region " << region_id;
+        const PrintRegion &region = this->printing_region(region_id);
+
+        //repeat detection for every nonplanar_surface
+        for (auto& nonplanar_surface: this->nonplanar_surfaces()) {
+            float distance_to_top = 0.0f;            
+            for (int shell_thickness = 0; region.config().top_solid_layers > shell_thickness; ++shell_thickness){
+                //search home layer where the area is projected to
+                for (LayerPtrs::reverse_iterator home_layer_it = this->m_layers.rbegin(); home_layer_it != this->m_layers.rend(); ++home_layer_it){
+                    Layer* home_layer        = *home_layer_it;
+                    LayerRegion &home_layerm = *home_layer->m_regions[region_id];
+                    //continue if home layer is not maximum height of nonplanar_surface - the desired distance to the top of the surface for more than one top solid layer
+                    if (home_layer->slice_z > nonplanar_surface.stats.max.z - distance_to_top) continue;
+
+                    //process layers
+                    for (LayerPtrs::iterator layer_it = this->m_layers.begin(); layer_it != this->m_layers.end(); ++layer_it){
+                        Layer* layer        = *layer_it;
+                        LayerRegion &layerm = *layer->m_regions[region_id];
+
+                        //skip if below minimum nonplanar surface and below the last possible surface layer
+                        if (nonplanar_surface.stats.min.z-layer->height-distance_to_top > layer->slice_z) continue;
+                        //break if above home layer
+                        if (home_layer->slice_z < layer->slice_z) break;
+                        //skip if bottom layer because we dont want to project the bottom layers up
+                        if (layer->lower_layer == NULL) continue;
+
+                        BOOST_LOG_TRIVIAL(trace) << "detect_nonplanar_surfaces for region " << region_id << " and layer " << layer->print_z;
+
+                        Surfaces layerm_slices_surfaces = layerm.slices().surfaces;
+                        SurfaceCollection topNonplanar;
+                        if (layer->upper_layer != NULL) {
+                            //append layers where nothing is above
+                            Layer* upper_layer = layer->upper_layer;
+                            LayerRegion &upper_layerm = *upper_layer->m_regions[region_id];
+                            Surfaces upper_surfaces = upper_layerm.slices().surfaces;
+                            topNonplanar.append(
+                                intersection_ex(
+                                    nonplanar_surface.horizontal_projection(),
+                                    union_ex(
+                                        diff_ex(
+                                            layerm_slices_surfaces, 
+                                            upper_surfaces, 
+                                            ApplySafetyOffset::No)), 
+                                    ApplySafetyOffset::No),
+                                (shell_thickness == 0 ? stTopNonplanar : stInternalSolidNonplanar),
+                                distance_to_top
+                            );
+
+                            // append layers where nonplanar areas with a lower distance_to_top are above
+                            SurfaceCollection upper_nonplanar;
+                            for (auto& s : upper_surfaces){
+                                if (s.is_nonplanar() && s.distance_to_top < distance_to_top) {
+                                    upper_nonplanar.surfaces.push_back(s);
+                                }
+                            }
+                            if (upper_nonplanar.size() > 0)
+                                topNonplanar.append(
+                                    intersection_ex(
+                                        nonplanar_surface.horizontal_projection(),
+                                        to_expolygons(upper_nonplanar.surfaces),
+                                        ApplySafetyOffset::No),
+                                    (shell_thickness == 0 ? stTopNonplanar : stInternalSolidNonplanar),
+                                    distance_to_top
+                                );
+                        }
+                        else {
+                            topNonplanar.append(
+                                intersection_ex(
+                                    nonplanar_surface.horizontal_projection(),
+                                    union_ex(to_expolygons(layerm_slices_surfaces)),
+                                    ApplySafetyOffset::No),
+                                (shell_thickness == 0 ? stTopNonplanar : stInternalSolidNonplanar),
+                                distance_to_top
+                            );
+                        }
+
+                        if (topNonplanar.size() > 0) {
+                            // layerm.export_region_slices_to_svg_debug("home_layer_append-layerm");
+                            // home_layerm.export_region_slices_to_svg_debug("home_layer_append-home_layerm");
+
+                            BOOST_LOG_TRIVIAL(trace) << "Removing " << topNonplanar.size() << " nonplanar surfaces from layer " << layer->print_z;
+
+                            layerm.remove_nonplanar_slices(topNonplanar);
+
+                            BOOST_LOG_TRIVIAL(trace) << "Adding " << topNonplanar.size() << " nonplanar surfaces to layer " << home_layer->print_z;
+
+                            // move nonplanar surfaces to home layer
+                            home_layerm.append_top_nonplanar_slices(topNonplanar);
+
+                            //save nonplanar_surface to home_layers nonplanar_surface list
+                            home_layerm.append_nonplanar_surface(nonplanar_surface);
+
+                            moved_surfaces = true;
+                        }
+                    }
+
+                    //increase distance to the top layer
+                    distance_to_top += home_layer->height;
+                    break;
+                }
+            }
+        }
+    }
+
+    if(moved_surfaces) {
+        // After changing a layer's slices, we must rebuild its lslices into islands
+        this->make_slices();
+        this->lslices_were_updated();
+    }
+
+    // Debugging output.
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+    for (size_t region_id = 0; region_id < this->num_printing_regions(); ++ region_id) {
+        for (const Layer *layer : m_layers) {
+            LayerRegion *layerm = layer->m_regions[region_id];
+            layerm->export_region_slices_to_svg_debug("0_detect_nonplanar_surfaces");
+            layerm->export_region_fill_surfaces_to_svg_debug("0_detect_nonplanar_surfaces");
+        } // for each layer
+    } // for each region
+#endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
+
+    //set typed_slices to true to force merge
+    m_typed_slices = true;
+}
+
+void
+PrintObject::project_nonplanar_surfaces()
+{
+    if(!m_config.use_nonplanar_layers.value) return;
+
+    //TODO check when steps should be invalidated
+    if (is_step_done(posNonplanarProjection)) return;
+    set_started(posNonplanarProjection);
+
+	for (size_t region_id = 0; region_id < this->num_printing_regions(); ++region_id) {
+        BOOST_LOG_TRIVIAL(debug) << "Processing nonplanar surfaces for region " << region_id << " in parallel - start";
+        tbb::parallel_for(
+            tbb::blocked_range<size_t>(0, m_layers.size()),
+            [this, region_id](const tbb::blocked_range<size_t>& range) {
+                PRINT_OBJECT_TIME_LIMIT_MILLIS(PRINT_OBJECT_TIME_LIMIT_DEFAULT);
+                for (size_t idx_layer = range.begin(); idx_layer < range.end(); ++ idx_layer) {
+                    m_print->throw_if_canceled();
+                    LayerRegion *layerm = m_layers[idx_layer]->m_regions[region_id];
+
+                    BOOST_LOG_TRIVIAL(trace) << "Processing nonplanar surfaces for region " << region_id << " and layer " << \
+                       idx_layer << " (z = " << layerm->layer()->print_z << ")";
+
+                    layerm->project_nonplanar_surfaces();
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+                    layerm->export_region_fill_surfaces_to_svg_debug("11_project_nonplanar_surfaces-final");
+#endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
+                } // for each layer of a region
+            });
+    }
+
+    BOOST_LOG_TRIVIAL(debug) << "Processing nonplanar surfaces - end";
+
+    set_done(posNonplanarProjection);
+}
+
 void PrintObject::process_external_surfaces()
 {
     BOOST_LOG_TRIVIAL(info) << "Processing external surfaces..." << log_memory_info();
@@ -1223,6 +1498,7 @@ void PrintObject::discover_vertical_shells()
             [this, &cache_top_botom_regions](const tbb::blocked_range<size_t>& range) {
                 PRINT_OBJECT_TIME_LIMIT_MILLIS(PRINT_OBJECT_TIME_LIMIT_DEFAULT);
                 const std::initializer_list<SurfaceType> surfaces_bottom { stBottom, stBottomBridge };
+                const std::initializer_list<SurfaceType> surfaces_top { stTop, stTopNonplanar };
                 const size_t num_regions = this->num_printing_regions();
                 for (size_t idx_layer = range.begin(); idx_layer < range.end(); ++ idx_layer) {
                     m_print->throw_if_canceled();
@@ -1239,7 +1515,7 @@ void PrintObject::discover_vertical_shells()
                         LayerRegion &layerm               = *layer.m_regions[region_id];
                         float        top_bottom_expansion = float(layerm.flow(frSolidInfill).scaled_spacing()) * top_bottom_expansion_coeff;
                         // Top surfaces.
-                        append(cache.top_surfaces, offset(layerm.slices().filter_by_type(stTop), top_bottom_expansion));
+                        append(cache.top_surfaces, offset(layerm.slices().filter_by_types(surfaces_top), top_bottom_expansion));
 //                        append(cache.top_surfaces, offset(layerm.fill_surfaces().filter_by_type(stTop), top_bottom_expansion));
                         // Bottom surfaces.
                         append(cache.bottom_surfaces, offset(layerm.slices().filter_by_types(surfaces_bottom), top_bottom_expansion));
@@ -1297,6 +1573,7 @@ void PrintObject::discover_vertical_shells()
                 [this, region_id, &cache_top_botom_regions](const tbb::blocked_range<size_t>& range) {
                     PRINT_OBJECT_TIME_LIMIT_MILLIS(PRINT_OBJECT_TIME_LIMIT_DEFAULT);
                     const std::initializer_list<SurfaceType> surfaces_bottom { stBottom, stBottomBridge };
+                    const std::initializer_list<SurfaceType> surfaces_top { stTop, stTopNonplanar };
                     for (size_t idx_layer = range.begin(); idx_layer < range.end(); ++ idx_layer) {
                         m_print->throw_if_canceled();
                         Layer       &layer                = *m_layers[idx_layer];
@@ -1304,7 +1581,7 @@ void PrintObject::discover_vertical_shells()
                         float        top_bottom_expansion = float(layerm.flow(frSolidInfill).scaled_spacing()) * top_bottom_expansion_coeff;
                         // Top surfaces.
                         auto &cache = cache_top_botom_regions[idx_layer];
-                        cache.top_surfaces = offset(layerm.slices().filter_by_type(stTop), top_bottom_expansion);
+                        cache.top_surfaces = offset(layerm.slices().filter_by_types(surfaces_top), top_bottom_expansion);
 //                        append(cache.top_surfaces, offset(layerm.fill_surfaces().filter_by_type(stTop), top_bottom_expansion));
                         // Bottom surfaces.
                         cache.bottom_surfaces = offset(layerm.slices().filter_by_types(surfaces_bottom), top_bottom_expansion);
@@ -1502,17 +1779,31 @@ void PrintObject::discover_vertical_shells()
                         svg.draw_outline(shell_ex, "black", "blue", scale_(0.05));
                         svg.Close();
                     }
+                    {
+                        Slic3r::SVG svg(debug_out_path("discover_vertical_shells-internalsolidnonplanar-wshell-%d.svg", debug_idx), get_extents(shell));
+                        svg.draw(layerm->fill_surfaces().filter_by_type(stInternalSolidNonplanar), "yellow", 0.5);
+                        svg.draw_outline(layerm->fill_surfaces().filter_by_type(stInternalSolidNonplanar), "black", "blue", scale_(0.05));
+                        svg.draw(shell_ex, "blue", 0.5);
+                        svg.draw_outline(shell_ex, "black", "blue", scale_(0.05));
+                        svg.Close();
+                    }
+                    {
+                        Slic3r::SVG svg(debug_out_path("discover_vertical_shells-holes-wshell-%d.svg", debug_idx), get_extents(shell));
+                        svg.draw_outline(to_expolygons(holes), "black", "blue", scale_(0.05));
+                        svg.Close();
+                    }
 #endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
 
                     // Trim the shells region by the internal & internal void surfaces.
-                    const Polygons    polygonsInternal = to_polygons(layerm->fill_surfaces().filter_by_types({ stInternal, stInternalVoid, stInternalSolid }));
+                    const Polygons    polygonsInternal = to_polygons(layerm->fill_surfaces().filter_by_types({ stInternal, stInternalVoid, stInternalSolid, stInternalSolidNonplanar }));
+                    const Polygons    polygonsInternalNonplanar = to_polygons(layerm->fill_surfaces().filter_by_type(stInternalSolidNonplanar));
                     shell = intersection(shell, polygonsInternal, ApplySafetyOffset::Yes);
                     polygons_append(shell, diff(polygonsInternal, holes));
                     if (shell.empty())
                         continue;
 
                     // Append the internal solids, so they will be merged with the new ones.
-                    polygons_append(shell, to_polygons(layerm->fill_surfaces().filter_by_type(stInternalSolid)));
+                    polygons_append(shell, to_polygons(layerm->fill_surfaces().filter_by_types({ stInternalSolid, stInternalSolidNonplanar })));
 
                     // These regions will be filled by a rectilinear full infill. Currently this type of infill
                     // only fills regions, which fit at least a single line. To avoid gaps in the sparse infill,
@@ -1560,7 +1851,8 @@ void PrintObject::discover_vertical_shells()
                     if (regularized_shell.empty())
                         continue;
 
-                    ExPolygons new_internal_solid = intersection_ex(polygonsInternal, regularized_shell);
+                    ExPolygons new_internal_solid = intersection_ex(diff_ex(polygonsInternal, polygonsInternalNonplanar), regularized_shell);
+                    ExPolygons new_internal_solid_nonplanar = intersection_ex(polygonsInternalNonplanar, regularized_shell);
 #ifdef SLIC3R_DEBUG_SLICE_PROCESSING
                     {
                         Slic3r::SVG svg(debug_out_path("discover_vertical_shells-regularized-%d.svg", debug_idx), get_extents(shell_before));
@@ -1583,14 +1875,16 @@ void PrintObject::discover_vertical_shells()
                         SVG::export_expolygons(debug_out_path("discover_vertical_shells-new_internal-%d.svg", debug_idx), get_extents(shell), new_internal, "black", "blue", scale_(0.05));
         				SVG::export_expolygons(debug_out_path("discover_vertical_shells-new_internal_void-%d.svg", debug_idx), get_extents(shell), new_internal_void, "black", "blue", scale_(0.05));
         				SVG::export_expolygons(debug_out_path("discover_vertical_shells-new_internal_solid-%d.svg", debug_idx), get_extents(shell), new_internal_solid, "black", "blue", scale_(0.05));
+        				SVG::export_expolygons(debug_out_path("discover_vertical_shells-new_internal_solid_nonplanar-%d.svg", debug_idx), get_extents(shell), new_internal_solid_nonplanar, "black", "blue", scale_(0.05));
                     }
 #endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
 
                     // Assign resulting internal surfaces to layer.
-                    layerm->m_fill_surfaces.keep_types({ stTop, stBottom, stBottomBridge });
+                    layerm->m_fill_surfaces.keep_types({ stTop, stTopNonplanar, stBottom, stBottomBridge });
                     layerm->m_fill_surfaces.append(new_internal,       stInternal);
                     layerm->m_fill_surfaces.append(new_internal_void,  stInternalVoid);
                     layerm->m_fill_surfaces.append(new_internal_solid, stInternalSolid);
+                    layerm->m_fill_surfaces.append(new_internal_solid_nonplanar, stInternalSolidNonplanar);
                 } // for each layer
             });
         m_print->throw_if_canceled();
@@ -1688,7 +1982,7 @@ void PrintObject::bridge_over_infill()
                 unsupported_area   = diff(unsupported_area, lower_layer_solids);
 
                 for (const LayerRegion *region : layer->regions()) {
-                    SurfacesPtr region_internal_solids = region->fill_surfaces().filter_by_type(stInternalSolid);
+                    SurfacesPtr region_internal_solids = region->fill_surfaces().filter_by_types({stInternalSolid, stInternalSolidNonplanar});
                     for (const Surface *s : region_internal_solids) {
                         Polygons unsupported         = intersection(to_polygons(s->expolygon), unsupported_area);
                         // The following flag marks those surfaces, which overlap with unuspported area, but at least part of them is supported. 

src/libslic3r/PrintObjectSlice.cpp

@@ -5,6 +5,7 @@
 #include "MultiMaterialSegmentation.hpp"
 #include "Print.hpp"
 #include "ShortestPath.hpp"
+#include "AABBMesh.hpp"
 
 #include <boost/log/trivial.hpp>
 
@@ -518,6 +519,14 @@ void PrintObject::slice()
     if (! warning.empty())
         BOOST_LOG_TRIVIAL(info) << warning;
 #endif
+    this->lslices_were_updated();
+    if (m_layers.empty())
+        throw Slic3r::SlicingError("No layers were detected. You might want to repair your STL file(s) or check their size or thickness and retry.\n");    
+    this->set_done(posSlice);
+}
+
+void PrintObject::lslices_were_updated()
+{
     // Update bounding boxes, back up raw slices of complex models.
     tbb::parallel_for(
         tbb::blocked_range<size_t>(0, m_layers.size()),
@@ -541,9 +550,6 @@ void PrintObject::slice()
                 Layer::build_up_down_graph(*m_layers[layer_idx - 1], *m_layers[layer_idx]);
             }
         });
-    if (m_layers.empty())
-        throw Slic3r::SlicingError("No layers were detected. You might want to repair your STL file(s) or check their size or thickness and retry.\n");    
-    this->set_done(posSlice);
 }
 
 template<typename ThrowOnCancel>
@@ -740,7 +746,16 @@ void PrintObject::slice_volumes()
         apply_mm_segmentation(*this, [print]() { print->throw_if_canceled(); });
     }
 
+    this->find_nonplanar_surfaces();
 
+    this->make_slices();
+
+    BOOST_LOG_TRIVIAL(debug) << "Slicing volumes - end";
+}
+
+void PrintObject::make_slices()
+{
+    const Print *print = this->print();
     BOOST_LOG_TRIVIAL(debug) << "Slicing volumes - make_slices in parallel - begin";
     {
         // Compensation value, scaled. Only applying the negative scaling here, as the positive scaling has already been applied during slicing.
@@ -802,6 +817,7 @@ void PrintObject::slice_volumes()
 	                            layer->m_regions[region_id]->trim_surfaces(trimming);
 	                    }
 	                }
+
 	                // Merge all regions' slices to get islands sorted topologically, chain them by a shortest path in separate index list
 	                layer->make_slices();
 	            }
@@ -822,6 +838,106 @@ void PrintObject::slice_volumes()
     BOOST_LOG_TRIVIAL(debug) << "Slicing volumes - make_slices in parallel - end";
 }
 
+void
+PrintObject::find_nonplanar_surfaces()
+{
+    //skip if not active
+    if(!m_config.use_nonplanar_layers.value) {
+        BOOST_LOG_TRIVIAL(debug) << "Find nonplanar surfaces - disabled";
+        return;
+    }
+
+    BOOST_LOG_TRIVIAL(info) << "Find nonplanar surfaces - start";
+
+    //Itterate over all model volumes
+    const ModelVolumePtrs volumes = this->model_object()->volumes;
+    for (ModelVolumePtrs::const_iterator it = volumes.begin(); it != volumes.end(); ++ it) {
+        //only check non modifier volumes
+        if (! (*it)->is_modifier()) {
+            const TriangleMesh tmesh = (*it)->mesh();
+            AABBMesh mesh(tmesh, true);
+            std::map<int, NonplanarFacet> facets;
+
+            // store all meshes with slope <= nonplanar_layers_angle in map. Map is necessary to keep facet ID
+            for (int face_id = 0; face_id < mesh.indices().size(); ++ face_id) {
+                auto &face = mesh.indices(face_id);
+                Vec3d normal = mesh.normal_by_face_id(face_id);
+
+                //TODO check if normals exist
+                if (normal.z() >= std::cos(m_config.nonplanar_layers_angle.value * 3.14159265/180.0)) {
+                    //copy facet
+                    NonplanarFacet new_facet;
+                    new_facet.normal.x = normal.x();
+                    new_facet.normal.y = normal.y();
+                    new_facet.normal.z = normal.z();
+
+                    Vec3i neighbor = mesh.face_neighbor_index()[face_id];
+                    its_triangle vertex = its_triangle_vertices(*mesh.get_triangle_mesh(), face_id);
+                    for (int j=0; j<=2 ;j++) {
+                        new_facet.vertex[j].x = vertex[j].x();
+                        new_facet.vertex[j].y = vertex[j].y();
+                        new_facet.vertex[j].z = vertex[j].z();
+                        new_facet.neighbor[j] = neighbor[j];
+                    }
+                    new_facet.calculate_stats();
+                    facets[face_id] = new_facet;
+                }
+            }
+
+            // create nonplanar surface from facets
+            NonplanarSurface nf = NonplanarSurface(facets);
+            BOOST_LOG_TRIVIAL(trace) << "Find nonplanar surfaces - moving surfaces by z=" << -tmesh.stats().min.z();
+            nf.translate(0, 0, -tmesh.stats().min.z());
+
+            // group surfaces and attach all nonplanar surfaces to the PrintObject
+            m_nonplanar_surfaces = nf.group_surfaces();
+
+            // check if surfaces maintain maximum printing height, if not, erase it
+            for (NonplanarSurfaces::iterator it = m_nonplanar_surfaces.begin(); it!=m_nonplanar_surfaces.end();) {
+                if((*it).check_max_printing_height(m_config.nonplanar_layers_height.value)) {
+                    it = m_nonplanar_surfaces.erase(it);
+                }else {
+                    it++;
+                }
+            }
+
+            // check if surfaces area is not too small
+            for (NonplanarSurfaces::iterator it = m_nonplanar_surfaces.begin(); it!=m_nonplanar_surfaces.end();) {
+                if((*it).check_surface_area()) {
+                    it = m_nonplanar_surfaces.erase(it);
+                }else {
+                    it++;
+                }
+            }
+
+            // check if surfaces areas collide
+            for (NonplanarSurfaces::iterator it = m_nonplanar_surfaces.begin(); it!=m_nonplanar_surfaces.end();) {
+                if(check_nonplanar_collisions((*it))) {
+                    it = m_nonplanar_surfaces.erase(it);
+                } else {
+                    it++;
+                }
+            }
+
+            //nf.debug_output();
+
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+            for (size_t id = 0; id < m_nonplanar_surfaces.size(); ++ id) {
+                auto& surface = m_nonplanar_surfaces[id];
+                Surfaces surfaces;
+                surfaces_append(surfaces, surface.horizontal_projection(), SurfaceType::stTopNonplanar);
+                SurfaceCollection c(surfaces);
+                c.export_to_svg(debug_out_path("0_find_nonplanar_surface-%d.svg", id).c_str(), true);
+            }
+#endif
+
+            BOOST_LOG_TRIVIAL(info) << "Find nonplanar surfaces - found " << m_nonplanar_surfaces.size() << " in " << (*it)->name;
+        }
+    }
+
+    BOOST_LOG_TRIVIAL(info) << "Find nonplanar surfaces - end";
+}
+
 std::vector<Polygons> PrintObject::slice_support_volumes(const ModelVolumeType model_volume_type) const
 {
     auto it_volume     = this->model_object()->volumes.begin();

src/libslic3r/SupportSpotsGenerator.cpp

@@ -243,9 +243,9 @@ float get_flow_width(const LayerRegion *region, ExtrusionRole role)
     if (role == ExtrusionRole::ExternalPerimeter) return region->flow(FlowRole::frExternalPerimeter).width();
     if (role == ExtrusionRole::GapFill) return region->flow(FlowRole::frInfill).width();
     if (role == ExtrusionRole::Perimeter) return region->flow(FlowRole::frPerimeter).width();
-    if (role == ExtrusionRole::SolidInfill) return region->flow(FlowRole::frSolidInfill).width();
+    if (role == ExtrusionRole::SolidInfill || role == ExtrusionRole::SolidInfillNonplanar) return region->flow(FlowRole::frSolidInfill).width();
     if (role == ExtrusionRole::InternalInfill) return region->flow(FlowRole::frInfill).width();
-    if (role == ExtrusionRole::TopSolidInfill) return region->flow(FlowRole::frTopSolidInfill).width();
+    if (role == ExtrusionRole::TopSolidInfill || role == ExtrusionRole::TopSolidInfillNonplanar) return region->flow(FlowRole::frTopSolidInfill).width();
     // default
     return region->flow(FlowRole::frPerimeter).width();
 }

src/libslic3r/Surface.cpp

@@ -35,10 +35,12 @@ const char* surface_type_to_color_name(const SurfaceType surface_type)
 {
     switch (surface_type) {
         case stTop:             return "rgb(255,0,0)"; // "red";
+        case stTopNonplanar:    return "rgb(166,2,255)"; // "purple";
         case stBottom:          return "rgb(0,255,0)"; // "green";
         case stBottomBridge:    return "rgb(0,0,255)"; // "blue";
         case stInternal:        return "rgb(255,255,128)"; // yellow 
         case stInternalSolid:   return "rgb(255,0,255)"; // magenta
+        case stInternalSolidNonplanar: return "rgb(255,133,2)"; // orange
         case stInternalBridge:  return "rgb(0,255,255)";
         case stInternalVoid:    return "rgb(128,128,128)";
         case stPerimeter:       return "rgb(128,0,0)"; // maroon
@@ -48,7 +50,7 @@ const char* surface_type_to_color_name(const SurfaceType surface_type)
 
 Point export_surface_type_legend_to_svg_box_size()
 {
-    return Point(scale_(1.+10.*8.), scale_(3.)); 
+    return Point(scale_(1.+16.*8.), scale_(3.)); 
 }
 
 void export_surface_type_legend_to_svg(SVG &svg, const Point &pos)
@@ -57,11 +59,13 @@ void export_surface_type_legend_to_svg(SVG &svg, const Point &pos)
     coord_t pos_x0 = pos(0) + scale_(1.);
     coord_t pos_x = pos_x0;
     coord_t pos_y = pos(1) + scale_(1.5);
-    coord_t step_x = scale_(10.);
+    coord_t step_x = scale_(16.);
     svg.draw_legend(Point(pos_x, pos_y), "perimeter"      , surface_type_to_color_name(stPerimeter));
     pos_x += step_x;
     svg.draw_legend(Point(pos_x, pos_y), "top"            , surface_type_to_color_name(stTop));
     pos_x += step_x;
+    svg.draw_legend(Point(pos_x, pos_y), "top nonplanar"  , surface_type_to_color_name(stTopNonplanar));
+    pos_x += step_x;
     svg.draw_legend(Point(pos_x, pos_y), "bottom"         , surface_type_to_color_name(stBottom));
     pos_x += step_x;
     svg.draw_legend(Point(pos_x, pos_y), "bottom bridge"  , surface_type_to_color_name(stBottomBridge));
@@ -74,6 +78,8 @@ void export_surface_type_legend_to_svg(SVG &svg, const Point &pos)
     pos_x += step_x;
     svg.draw_legend(Point(pos_x, pos_y), "internal solid" , surface_type_to_color_name(stInternalSolid));
     pos_x += step_x;
+    svg.draw_legend(Point(pos_x, pos_y), "internal solid nonplanar" , surface_type_to_color_name(stInternalSolidNonplanar));
+    pos_x += step_x;
     svg.draw_legend(Point(pos_x, pos_y), "internal bridge", surface_type_to_color_name(stInternalBridge));
     pos_x += step_x;
     svg.draw_legend(Point(pos_x, pos_y), "internal void"  , surface_type_to_color_name(stInternalVoid));

src/libslic3r/Surface.hpp

@@ -24,6 +24,10 @@ enum SurfaceType {
     stInternalVoid,
     // Inner/outer perimeters.
     stPerimeter,
+    // 
+    stTopNonplanar,
+    //
+    stInternalSolidNonplanar,
     // Number of SurfaceType enums.
     stCount,
 };
@@ -37,6 +41,7 @@ public:
     unsigned short  thickness_layers {  1 };  // in layers
     double          bridge_angle     { -1. }; // in radians, ccw, 0 = East, only 0+ (negative means undefined)
     unsigned short  extra_perimeters {  0 };
+    float           distance_to_top  {  0 };
     
     Surface(const Slic3r::Surface &rhs) :
         surface_type(rhs.surface_type), expolygon(rhs.expolygon),
@@ -67,6 +72,7 @@ public:
         thickness_layers = rhs.thickness_layers;
         bridge_angle     = rhs.bridge_angle;
         extra_perimeters = rhs.extra_perimeters;
+        distance_to_top  = rhs.distance_to_top;
         return *this;
     }
 
@@ -78,6 +84,7 @@ public:
         thickness_layers = rhs.thickness_layers;
         bridge_angle     = rhs.bridge_angle;
         extra_perimeters = rhs.extra_perimeters;
+        distance_to_top  = rhs.distance_to_top;
         return *this;
     }
 
@@ -86,12 +93,14 @@ public:
     void   clear() 			   { expolygon.clear(); }
 
     // The following methods do not test for stPerimeter.
-	bool   is_top()      const { return this->surface_type == stTop; }
+	bool   is_top()      const { return this->surface_type == stTop || this->surface_type == stTopNonplanar; }
 	bool   is_bottom()   const { return this->surface_type == stBottom || this->surface_type == stBottomBridge; }
 	bool   is_bridge()   const { return this->surface_type == stBottomBridge || this->surface_type == stInternalBridge; }
 	bool   is_external() const { return this->is_top() || this->is_bottom(); }
 	bool   is_internal() const { return ! this->is_external(); }
-	bool   is_solid()    const { return this->is_external() || this->surface_type == stInternalSolid || this->surface_type == stInternalBridge; }
+	bool   is_internal_solid() const { return this->surface_type == stInternalSolid || this->surface_type == stInternalSolidNonplanar; }
+	bool   is_solid()    const { return this->is_external() || this->surface_type == stInternalSolid || this->surface_type == stInternalSolidNonplanar || this->surface_type == stInternalBridge; }
+	bool   is_nonplanar() const { return this->surface_type == stTopNonplanar || this->surface_type == stInternalSolidNonplanar; }
 };
 
 typedef std::vector<Surface> Surfaces;
@@ -228,9 +237,20 @@ inline void polygons_append(Polygons &dst, SurfacesPtr &&src)
 inline void surfaces_append(Surfaces &dst, const ExPolygons &src, SurfaceType surfaceType) 
 { 
     dst.reserve(dst.size() + src.size());
-    for (const ExPolygon &expoly : src)
+    for (const ExPolygon &expoly : src) {
         dst.emplace_back(Surface(surfaceType, expoly));
     }
+}
+inline void surfaces_append(Surfaces &dst, const ExPolygons &src, SurfaceType surfaceType, float distance_to_top) 
+{
+    dst.reserve(dst.size() + src.size());
+    for (const ExPolygon &expoly : src) {
+        Surface s = Surface(surfaceType, expoly);
+        s.distance_to_top = distance_to_top;
+        dst.emplace_back(s);
+    }
+}
+
 inline void surfaces_append(Surfaces &dst, const ExPolygons &src, const Surface &surfaceTempl) 
 { 
     dst.reserve(dst.size() + number_polygons(src));
@@ -278,7 +298,8 @@ inline bool surfaces_could_merge(const Surface &s1, const Surface &s2)
         s1.surface_type      == s2.surface_type     &&
         s1.thickness         == s2.thickness        &&
         s1.thickness_layers  == s2.thickness_layers &&
-        s1.bridge_angle      == s2.bridge_angle;
+        s1.bridge_angle      == s2.bridge_angle     &&
+        s1.distance_to_top   == s2.distance_to_top;
 }
 
 class SVG;

src/libslic3r/SurfaceCollection.hpp

@@ -68,9 +68,11 @@ public:
     void append(const SurfaceCollection &coll) { this->append(coll.surfaces); }
     void append(SurfaceCollection &&coll) { this->append(std::move(coll.surfaces)); }
     void append(const ExPolygons &src, SurfaceType surfaceType) { surfaces_append(this->surfaces, src, surfaceType); }
+    void append(const ExPolygons &src, SurfaceType surfaceType, float distance_to_top) { surfaces_append(this->surfaces, src, surfaceType, distance_to_top); }
     void append(const ExPolygons &src, const Surface &surfaceTempl) { surfaces_append(this->surfaces, src, surfaceTempl); }
     void append(const Surfaces &src) { surfaces_append(this->surfaces, src); }
     void append(ExPolygons &&src, SurfaceType surfaceType) { surfaces_append(this->surfaces, std::move(src), surfaceType); }
+    void append(ExPolygons &&src, SurfaceType surfaceType, float distance_to_top) { surfaces_append(this->surfaces, std::move(src), surfaceType, distance_to_top); }
     void append(ExPolygons &&src, const Surface &surfaceTempl) { surfaces_append(this->surfaces, std::move(src), surfaceTempl); }
     void append(Surfaces &&src) { surfaces_append(this->surfaces, std::move(src)); }
 

src/slic3r/GUI/GCodeViewer.cpp

@@ -569,7 +569,9 @@ const std::array<ColorRGBA, static_cast<size_t>(GCodeExtrusionRole::Count)> GCod
     { 0.12f, 0.12f, 1.00f, 1.0f },   // GCodeExtrusionRole::OverhangPerimeter
     { 0.69f, 0.19f, 0.16f, 1.0f },   // GCodeExtrusionRole::InternalInfill
     { 0.59f, 0.33f, 0.80f, 1.0f },   // GCodeExtrusionRole::SolidInfill
+    { 0.75f, 0.12f, 0.45f, 1.0f },   // GCodeExtrusionRole::SolidInfillNonplanar
     { 0.94f, 0.25f, 0.25f, 1.0f },   // GCodeExtrusionRole::TopSolidInfill
+    { 0.32f, 0.12f, 0.45f, 1.0f },   // GCodeExtrusionRole::TopSolidInfillNonplanar
     { 1.00f, 0.55f, 0.41f, 1.0f },   // GCodeExtrusionRole::Ironing
     { 0.30f, 0.50f, 0.73f, 1.0f },   // GCodeExtrusionRole::BridgeInfill
     { 1.00f, 1.00f, 1.00f, 1.0f },   // GCodeExtrusionRole::GapFill

src/slic3r/GUI/Tab.cpp

@@ -1459,6 +1459,12 @@ void TabPrint::build()
         optgroup->append_single_option_line("fuzzy_skin_thickness", category_path + "fuzzy-skin-thickness");
         optgroup->append_single_option_line("fuzzy_skin_point_dist", category_path + "fuzzy-skin-point-distance");
 
+        optgroup = page->new_optgroup(L("Nonplanar layers (experimental)"));
+        category_path = "nonplanar-layers_19282821/#";
+        optgroup->append_single_option_line("use_nonplanar_layers", category_path + "use-nonplanar-layers");
+        optgroup->append_single_option_line("nonplanar_layers_angle", category_path + "nonplanar-layers-height");
+        optgroup->append_single_option_line("nonplanar_layers_height", category_path + "nonplanar-layers-height");
+
     page = add_options_page(L("Infill"), "infill");
         category_path = "infill_42#";
         optgroup = page->new_optgroup(L("Infill"));