(From code review.) Small refactors and add documentation.

done as part of CURA-10407

include/GCodePathConfig.h

@@ -18,7 +18,7 @@ namespace cura
  */
 struct GCodePathConfig
 {
-    coord_t z_offset{};
+    coord_t z_offset{}; //<! vertical offset from 'full' layer height
     PrintFeatureType type{}; //!< name of the feature type
     coord_t line_width{}; //!< width of the line extruded
     coord_t layer_thickness{}; //!< current layer height in micron

include/LayerPlan.h

@@ -110,15 +110,16 @@ class LayerPlan : public NoCopy
      *
      * \param config The config used for the path returned
      * \param space_fill_type The type of space filling which this path employs
+     * \param z_offset (optional) Vertical offset w.r.t current layer height, defaults to 0
      * \param flow (optional) A ratio for the extrusion speed
      * \param spiralize Whether to gradually increase the z while printing. (Note that this path may be part of a sequence of spiralized paths, forming one polygon)
      * \param speed_factor (optional) a factor which the speed will be multiplied by.
      * \return A path with the given config which is now the last path in LayerPlan::paths
      */
     GCodePath* getLatestPathWithConfig(
         const GCodePathConfig& config,
-        const coord_t z_offset,
         const SpaceFillType space_fill_type,
+        const coord_t z_offset = 0,
         const Ratio flow = 1.0_r,
         const Ratio width_factor = 1.0_r,
         const bool spiralize = false,
@@ -282,7 +283,7 @@ class LayerPlan : public NoCopy
      * \param p The point to travel to.
      * \param force_retract Whether to force a retraction to occur.
      */
-    GCodePath& addTravel(const Point p, const bool force_retract = false, const coord_t z_offset = 0);
+    GCodePath& addTravel(const Point& p, const bool force_retract = false, const coord_t z_offset = 0);
 
     /*!
      * Add a travel path to a certain point and retract if needed.
@@ -292,7 +293,7 @@ class LayerPlan : public NoCopy
      * \param p The point to travel to
      * \param path (optional) The travel path to which to add the point \p p
      */
-    GCodePath& addTravel_simple(const Point p, GCodePath* path = nullptr);
+    GCodePath& addTravel_simple(const Point& p, GCodePath* path = nullptr);
 
     /*!
      * Plan a prime blob at the current location.

include/SupportInfillPart.h

@@ -34,7 +34,7 @@ class SupportInfillPart
     std::vector<VariableWidthLines> wall_toolpaths; //!< Any walls go here, not in the areas, where they could be combined vertically (don't combine walls). Binned by inset_idx.
 
     coord_t custom_line_distance;
-    bool use_fractional_config;
+    bool use_fractional_config; //!< Request to use the configuration used to fill a partial layer height here, instead of the normal full layer height configuration.
 
     SupportInfillPart(const PolygonsPart& outline, coord_t support_line_width, bool use_fractional_config, int inset_count_to_generate = 0, coord_t custom_line_distance = 0);
 

include/pathPlanning/GCodePath.h

@@ -29,7 +29,7 @@ namespace cura
  */
 struct GCodePath
 {
-    coord_t z_offset{};
+    coord_t z_offset{}; //<! vertical offset from 'full' layer height
     GCodePathConfig config{}; //!< The configuration settings of the path.
     std::shared_ptr<const SliceMeshStorage> mesh; //!< Which mesh this path belongs to, if any. If it's not part of any mesh, the mesh should be nullptr;
     SpaceFillType space_fill_type{}; //!< The type of space filling of which this path is a part

src/LayerPlan.cpp

@@ -38,8 +38,8 @@ constexpr int MINIMUM_SQUARED_LINE_LENGTH = MINIMUM_LINE_LENGTH * MINIMUM_LINE_L
 
 GCodePath* LayerPlan::getLatestPathWithConfig(
     const GCodePathConfig& config,
-    const coord_t z_offset,
     const SpaceFillType space_fill_type,
+    const coord_t z_offset,
     const Ratio flow,
     const Ratio width_factor,
     const bool spiralize,
@@ -329,14 +329,14 @@ std::optional<std::pair<Point, bool>> LayerPlan::getFirstTravelDestinationState(
     return ret;
 }
 
-GCodePath& LayerPlan::addTravel(const Point p, const bool force_retract, const coord_t z_offset)
+GCodePath& LayerPlan::addTravel(const Point& p, const bool force_retract, const coord_t z_offset)
 {
     const GCodePathConfig& travel_config = configs_storage.travel_config_per_extruder[getExtruder()];
 
     const RetractionConfig& retraction_config
         = current_mesh ? current_mesh->retraction_wipe_config.retraction_config : storage.retraction_wipe_config_per_extruder[getExtruder()].retraction_config;
 
-    GCodePath* path = getLatestPathWithConfig(travel_config, z_offset, SpaceFillType::None);
+    GCodePath* path = getLatestPathWithConfig(travel_config, SpaceFillType::None, z_offset);
 
     bool combed = false;
 
@@ -481,7 +481,7 @@ GCodePath& LayerPlan::addTravel(const Point p, const bool force_retract, const c
     return ret;
 }
 
-GCodePath& LayerPlan::addTravel_simple(const Point p, GCodePath* path)
+GCodePath& LayerPlan::addTravel_simple(const Point& p, GCodePath* path)
 {
     bool is_first_travel_of_layer = ! static_cast<bool>(last_planned_position);
     if (is_first_travel_of_layer)
@@ -491,7 +491,7 @@ GCodePath& LayerPlan::addTravel_simple(const Point p, GCodePath* path)
     }
     if (path == nullptr)
     {
-        path = getLatestPathWithConfig(configs_storage.travel_config_per_extruder[getExtruder()], 0, SpaceFillType::None);
+        path = getLatestPathWithConfig(configs_storage.travel_config_per_extruder[getExtruder()], SpaceFillType::None);
     }
     path->points.push_back(p);
     last_planned_position = p;
@@ -518,7 +518,7 @@ void LayerPlan::addExtrusionMove(
     const Ratio speed_factor,
     const double fan_speed)
 {
-    GCodePath* path = getLatestPathWithConfig(config, config.z_offset, space_fill_type, flow, width_factor, spiralize, speed_factor);
+    GCodePath* path = getLatestPathWithConfig(config, space_fill_type, config.z_offset, flow, width_factor, spiralize, speed_factor);
     path->points.push_back(p);
     path->setFanSpeed(fan_speed);
     if (! static_cast<bool>(first_extrusion_acc_jerk))