Handle the last tapered end of spiralize on our own instead of with 'non-spiralize' code.

Eventually, we should probably refactor this to use the scarf-seam code.

part of CURA-12369

Author: rburema

src/LayerPlan.cpp

@@ -2846,7 +2846,6 @@ void LayerPlan::writeGCode(GCodeExport& gcode)
         const ExtruderTrain& extruder = Application::getInstance().current_slice_->scene.extruders[extruder_nr];
 
         bool update_extrusion_offset = true;
-        bool spiralize_finisher = false;
 
         double cumulative_path_time = 0.; // Time in seconds.
         const std::function<void(const double, const int64_t)> insertTempOnTime = [&](const double to_add, const int64_t path_idx)
@@ -3009,7 +3008,7 @@ void LayerPlan::writeGCode(GCodeExport& gcode)
                 gcode.writeComment(ss.str());
             }
 
-            if (! (path.spiralize || spiralize_finisher) && path.travel_to_z && (! path.retract || ! path.perform_z_hop)
+            if (! path.spiralize && path.travel_to_z && (! path.retract || ! path.perform_z_hop)
                 && (z_ + path.z_offset + path.points.front().z_ != gcode.getPositionZ()) && (path_idx > 0 || layer_nr_ > 0))
             {
                 // First move to desired height to then make a plain horizontal move
@@ -3055,22 +3054,17 @@ void LayerPlan::writeGCode(GCodeExport& gcode)
                 }
                 if (! coasting) // not same as 'else', cause we might have changed [coasting] in the line above...
                 { // normal path to gcode algorithm
-                    const coord_t extra_z_offset = spiralize_finisher ? layer_thickness_ : 0;
-
                     Point3LL prev_point = gcode.getPosition();
-                    for (unsigned int point_idx = 0; point_idx < path.points.size(); point_idx++)
+                    for (const auto& pt : path.points)
                     {
-                        Point3LL& pt = path.points[point_idx];
-                        pt.z_ += extra_z_offset;
-
                         const auto [_, time] = extruder_plan.getPointToPointTime(prev_point, pt, path);
                         insertTempOnTime(time, path_idx);
 
                         const double extrude_speed = speed * path.speed_back_pressure_factor;
                         writeExtrusionRelativeZ(gcode, pt, extrude_speed, path.z_offset, path.getExtrusionMM3perMM(), path.config.type, update_extrusion_offset);
                         sendLineTo(path, pt, extrude_speed);
 
-                        prev_point = path.points[point_idx];
+                        prev_point = pt;
                     }
                 }
             }
@@ -3092,32 +3086,45 @@ void LayerPlan::writeGCode(GCodeExport& gcode)
 
                 double length = 0.0;
                 p0 = gcode.getPositionXY();
-                for (; path_idx < paths.size() && paths[path_idx].spiralize; path_idx++)
-                { // handle all consecutive spiralized paths > CHANGES path_idx!
-                    GCodePath& spiral_path = paths[path_idx];
-
-                    for (unsigned int point_idx = 0; point_idx < spiral_path.points.size(); point_idx++)
+                const auto writeSpiralPath =
+                [&](const GCodePath& spiral_path, const bool end_layer) -> void
+                {
+                    for (const auto& p1 : spiral_path.points)
                     {
-                        const Point3LL p1 = spiral_path.points[point_idx];
-
                         const Point2LL p1_2d = p1.toPoint2LL();
                         length += vSizeMM(p0 - p1_2d);
                         p0 = p1_2d;
 
-                        const coord_t z_offset = std::round(layer_thickness_ * length / totalLength);
+                        const coord_t z_offset = end_layer ? layer_thickness_ / 2 : std::round(layer_thickness_ * length / totalLength);
                         const double extrude_speed = speed * spiral_path.speed_back_pressure_factor;
                         writeExtrusionRelativeZ(
                             gcode,
-                            spiral_path.points[point_idx],
+                            p1,
                             extrude_speed,
                             path.z_offset + z_offset,
                             spiral_path.getExtrusionMM3perMM(),
                             spiral_path.config.type,
                             update_extrusion_offset);
                         sendLineTo(spiral_path, Point3LL(p1.x_, p1.y_, z_offset), extrude_speed, layer_thickness_);
                     }
+                };
+
+                for (; path_idx < paths.size() && paths[path_idx].spiralize; path_idx++)
+                { // handle all consecutive spiralized paths > CHANGES path_idx!
+                    constexpr bool not_end_layer = false;
+                    writeSpiralPath(paths[path_idx], not_end_layer);
+                }
+
+                if (path_idx < paths.size())
+                {
+                    // Handle last path & exit.
+                    constexpr bool end_layer = true;
+                    for (; path_idx < paths.size(); path_idx++)
+                    {
+                        writeSpiralPath(paths[path_idx], end_layer);
+                    }
+                    break;
                 }
-                spiralize_finisher = true;
                 path_idx--; // the last path_idx didnt spiralize, so it's not part of the current spiralize path
             }
         } // paths for this extruder /\  .