New feature: Bridging angle override through a bridge_angle config

variable. When set to zero, the usual automatic bridge detection applies.
The bridging angle override may be set at the Infill->Advanced settings,
or through a modifier mesh.

lib/Slic3r/GUI/Tab.pm

@@ -532,7 +532,7 @@ sub build {
         seam_position external_perimeters_first
         fill_density fill_pattern external_fill_pattern
         infill_every_layers infill_only_where_needed
-        solid_infill_every_layers fill_angle solid_infill_below_area 
+        solid_infill_every_layers fill_angle bridge_angle solid_infill_below_area 
         only_retract_when_crossing_perimeters infill_first
         max_print_speed max_volumetric_speed 
         max_volumetric_extrusion_rate_slope_positive max_volumetric_extrusion_rate_slope_negative
@@ -622,6 +622,7 @@ sub build {
             $optgroup->append_single_option_line('solid_infill_every_layers');
             $optgroup->append_single_option_line('fill_angle');
             $optgroup->append_single_option_line('solid_infill_below_area');
+            $optgroup->append_single_option_line('bridge_angle');
             $optgroup->append_single_option_line('only_retract_when_crossing_perimeters');
             $optgroup->append_single_option_line('infill_first');
         }
@@ -977,7 +978,7 @@ sub _update {
             solid_infill_speed);
     
     $self->get_field($_)->toggle($have_infill || $have_solid_infill)
-        for qw(fill_angle infill_extrusion_width infill_speed bridge_speed);
+        for qw(fill_angle bridge_angle infill_extrusion_width infill_speed bridge_speed);
     
     $self->get_field('gap_fill_speed')->toggle($have_perimeters && $have_infill);
     

xs/src/libslic3r/BridgeDetector.cpp

@@ -68,20 +68,20 @@ void BridgeDetector::initialize()
     */
 }
 
-bool
+bool BridgeDetector::detect_angle(double bridge_direction_override)
-BridgeDetector::detect_angle()
 {
     if (this->_edges.empty() || this->_anchor_regions.empty()) 
         // The bridging region is completely in the air, there are no anchors available at the layer below.
         return false;
 
     std::vector<BridgeDirection> candidates;
-    {
+    if (bridge_direction_override == 0.) {
         std::vector<double> angles = bridge_direction_candidates();
         candidates.reserve(angles.size());
         for (size_t i = 0; i < angles.size(); ++ i)
-            candidates.push_back(BridgeDirection(angles[i]));
+            candidates.emplace_back(BridgeDirection(angles[i]));
-    }
+    } else
+        candidates.emplace_back(BridgeDirection(bridge_direction_override));
     
     /*  Outset the bridge expolygon by half the amount we used for detecting anchors;
         we'll use this one to clip our test lines and be sure that their endpoints

xs/src/libslic3r/BridgeDetector.hpp

@@ -31,7 +31,8 @@ public:
     
     BridgeDetector(ExPolygon _expolygon, const ExPolygonCollection &_lower_slices, coord_t _extrusion_width);
     BridgeDetector(const ExPolygons &_expolygons, const ExPolygonCollection &_lower_slices, coord_t _extrusion_width);
-    bool detect_angle();
+    // If bridge_direction_override != 0, then the angle is used instead of auto-detect.
+    bool detect_angle(double bridge_direction_override = 0.);
     Polygons coverage(double angle = -1) const;
     void unsupported_edges(double angle, Polylines* unsupported) const;
     Polylines unsupported_edges(double angle = -1) const;

xs/src/libslic3r/LayerRegion.cpp

@@ -1,6 +1,7 @@
 #include "Layer.hpp"
 #include "BridgeDetector.hpp"
 #include "ClipperUtils.hpp"
+#include "Geometry.hpp"
 #include "PerimeterGenerator.hpp"
 #include "Print.hpp"
 #include "Surface.hpp"
@@ -87,8 +88,7 @@ LayerRegion::make_perimeters(const SurfaceCollection &slices, SurfaceCollection*
 //#define EXTERNAL_SURFACES_OFFSET_PARAMETERS ClipperLib::jtMiter, 1.5
 #define EXTERNAL_SURFACES_OFFSET_PARAMETERS ClipperLib::jtSquare, 0.
 
-void
+void LayerRegion::process_external_surfaces(const Layer* lower_layer)
-LayerRegion::process_external_surfaces(const Layer* lower_layer)
 {
     const Surfaces &surfaces = this->fill_surfaces.surfaces;
     const double margin = scale_(EXTERNAL_INFILL_MARGIN);
@@ -260,7 +260,7 @@ LayerRegion::process_external_surfaces(const Layer* lower_layer)
                 #ifdef SLIC3R_DEBUG
                 printf("Processing bridge at layer " PRINTF_ZU ":\n", this->layer()->id());
                 #endif
-                if (bd.detect_angle()) {
+                if (bd.detect_angle(Geometry::deg2rad(this->region()->config.bridge_angle))) {
                     bridges[idx_last].bridge_angle = bd.angle;
                     if (this->layer()->object()->config.support_material) {
                         polygons_append(this->bridged, bd.coverage());

xs/src/libslic3r/PrintConfig.cpp

@@ -65,6 +65,15 @@ PrintConfigDef::PrintConfigDef()
     def->min = 0;
     def->default_value = new ConfigOptionFloat(0);
 
+    def = this->add("bridge_angle", coFloat);
+    def->label = "Bridging angle";
+    def->category = "Infill";
+    def->tooltip = "Bridging angle override. If left to zero, the bridging angle will be calculated automatically. Otherwise the provided angle will be used for all bridges, use 180° for zero angle.";
+    def->sidetext = "°";
+    def->cli = "bridge-angle=f";
+    def->min = 0;
+    def->default_value = new ConfigOptionFloat(0.);
+
     def = this->add("bridge_fan_speed", coInts);
     def->label = "Bridges fan speed";
     def->tooltip = "This fan speed is enforced during all bridges and overhangs.";

xs/src/libslic3r/PrintConfig.hpp

@@ -244,6 +244,7 @@ public:
 class PrintRegionConfig : public virtual StaticPrintConfig
 {
 public:
+    ConfigOptionFloat               bridge_angle;
     ConfigOptionInt                 bottom_solid_layers;
     ConfigOptionFloat               bridge_flow_ratio;
     ConfigOptionFloat               bridge_speed;
@@ -285,6 +286,7 @@ class PrintRegionConfig : public virtual StaticPrintConfig
 
     virtual ConfigOption* optptr(const t_config_option_key &opt_key, bool create = false) {
         UNUSED(create);
+        OPT_PTR(bridge_angle);
         OPT_PTR(bottom_solid_layers);
         OPT_PTR(bridge_flow_ratio);
         OPT_PTR(bridge_speed);

xs/src/libslic3r/PrintObject.cpp

@@ -195,7 +195,8 @@ bool PrintObject::invalidate_state_by_config_options(const std::vector<t_config_
             || opt_key == "infill_extruder"
             || opt_key == "solid_infill_extruder"
             || opt_key == "infill_extrusion_width"
-            || opt_key == "ensure_vertical_shell_thickness") {
+            || opt_key == "ensure_vertical_shell_thickness"
+            || opt_key == "bridge_angle") {
             steps.emplace_back(posPrepareInfill);
         } else if (
                opt_key == "external_fill_pattern"