avoid unneeded unretract followed by a retract in mid-air for sparse wipe tower.

supermerill/SuperSlicer#1467

2 files changed, 11 insertions, 5 deletions

diff --git a/src/libslic3r/GCode.cpp b/src/libslic3r/GCode.cpp
index 3a16f51ba..acdc5d731 100644
--- a/src/libslic3r/GCode.cpp
+++ b/src/libslic3r/GCode.cpp
@@ -288,6 +288,7 @@ static inline void set_extra_lift(const float previous_print_z, const int layer_
             gcodegen.m_gcode_label_objects_end = "";
         }
 
+        bool need_unretract = false;
         if (! tcr.priming) {
             // Move over the wipe tower.
             // Retract for a tool change, using the toolchange retract value and setting the priming extra length.
@@ -298,17 +299,21 @@ static inline void set_extra_lift(const float previous_print_z, const int layer_
                 wipe_tower_point_to_object_point(gcodegen, start_pos),
                 erMixed);
             gcodegen.write_travel_to(gcode, polyline, "Travel to a Wipe Tower");
-            gcode += gcodegen.unretract();
+            need_unretract = true;
         }
 
-        double current_z = gcodegen.writer().get_position().z();
+        double current_z = gcodegen.writer().get_unlifted_position().z();
         if (z == -1.) // in case no specific z was provided, print at current_z pos
             z = current_z;
         if (! is_approx(z, current_z)) {
-            gcode += gcodegen.writer().retract();
+            if (!need_unretract)
+                gcode += gcodegen.writer().retract();
             gcode += gcodegen.writer().travel_to_z(z, "Travel down to the last wipe tower layer.");
-            gcode += gcodegen.writer().unretract();
+            need_unretract = true;
         }
+        // only unretract when travel is finished
+        if(need_unretract)
+            gcode += gcodegen.unretract();
 
 
         // Process the end filament gcode.
@@ -374,7 +379,7 @@ static inline void set_extra_lift(const float previous_print_z, const int layer_
         if (!is_approx(z, current_z)) {
             gcode += gcodegen.writer().retract();
             gcode += gcodegen.writer().travel_to_z(current_z, "Travel back up to the topmost object layer.");
-            gcode += gcodegen.writer().unretract();
+            //gcode += gcodegen.writer().unretract(); //why? it's done automatically later, where needed!
         } else {
         // Prepare a future wipe.
             gcodegen.m_wipe.reset_path();
diff --git a/src/libslic3r/GCodeWriter.hpp b/src/libslic3r/GCodeWriter.hpp
index f74eec403..fa4b1de0c 100644
--- a/src/libslic3r/GCodeWriter.hpp
+++ b/src/libslic3r/GCodeWriter.hpp
@@ -78,6 +78,7 @@ public:
     std::string lift(int layer_id);
     std::string unlift();
     Vec3d       get_position() const { return m_pos; }
+    Vec3d       get_unlifted_position() const { return m_pos - Vec3d{0, 0, m_extra_lift + m_lifted}; }
 
 private:
 	// Extruders are sorted by their ID, so that binary search is possible.