Implement cancel object for toolchanges.

Toolchages (wipe tower/no wipe tower) are always kept and if there are
any toolchanges, the objects are split at the begining of each instance,
while the first travel is always part of the "next" instance.

src/libslic3r/GCode.cpp

@@ -2181,6 +2181,12 @@ LayerResult GCodeGenerator::process_layer(
     // Either printing all copies of all objects, or just a single copy of a single object.
     assert(single_object_instance_idx == size_t(-1) || layers.size() == 1);
 
+    const std::vector<InstanceToPrint> instances_to_print{sort_print_object_instances(layers, ordering, single_object_instance_idx)};
+    const PrintInstance* first_instance{instances_to_print.empty() ? nullptr : &instances_to_print.front().print_object.instances()[instances_to_print.front().instance_id]};
+    if (first_instance != nullptr) {
+        m_label_objects.update(*first_instance);
+    }
+
     // First object, support and raft layer, if available.
     const Layer         *object_layer  = nullptr;
     const SupportLayer  *support_layer = nullptr;
@@ -2383,8 +2389,6 @@ LayerResult GCodeGenerator::process_layer(
             m_avoid_crossing_perimeters.disable_once();
         }
 
-        std::vector<InstanceToPrint> instances_to_print = sort_print_object_instances(layers, ordering, single_object_instance_idx);
-
         // We are almost ready to print. However, we must go through all the objects twice to print the the overridden extrusions first (infill/perimeter wiping feature):
         bool is_anything_overridden = layer_tools.wiping_extrusions().is_anything_overridden();
         if (is_anything_overridden) {
@@ -2785,6 +2789,10 @@ std::string GCodeGenerator::change_layer(
         // Increment a progress bar indicator.
         gcode += m_writer.update_progress(++ m_layer_index, m_layer_count);
 
+    if (m_writer.multiple_extruders) {
+        gcode += m_label_objects.maybe_change_instance();
+    }
+
     if (!EXTRUDER_CONFIG(travel_ramping_lift) && EXTRUDER_CONFIG(retract_layer_change)) {
         gcode += this->retract_and_wipe();
     } else if (EXTRUDER_CONFIG(travel_ramping_lift) && !vase_mode){
@@ -3123,7 +3131,17 @@ std::string GCodeGenerator::_extrude(
     std::string gcode;
     const std::string_view description_bridge = path_attr.role.is_bridge() ? " (bridge)"sv : ""sv;
 
-    const std::string instance_change_gcode{this->m_label_objects.maybe_change_instance()};
+    const bool has_active_instance{m_label_objects.has_active_instance()};
+    if (m_writer.multiple_extruders && has_active_instance) {
+        gcode += m_label_objects.maybe_change_instance();
+    }
+
+    std::string instance_change_gcode{this->m_label_objects.maybe_change_instance()};
+    const std::string delayed_instance_change_gcode{instance_change_gcode};
+    if (m_writer.multiple_extruders) {
+        instance_change_gcode = "";
+    }
+
     if (!m_current_layer_first_position) {
         const Vec3crd point = to_3d(path.front().point, scaled(this->m_last_layer_z));
         gcode += this->travel_to_first_position(point, unscaled(point.z()), instance_change_gcode);
@@ -3154,6 +3172,10 @@ std::string GCodeGenerator::_extrude(
         gcode += "FIRST_UNRETRACT" + this->unretract();
     }
 
+    if (m_writer.multiple_extruders && !has_active_instance) {
+        gcode += delayed_instance_change_gcode;
+    }
+
     if (!m_pending_pre_extrusion_gcode.empty()) {
         // There is G-Code that is due to be inserted before an extrusion starts. Insert it.
         gcode += m_pending_pre_extrusion_gcode;

src/libslic3r/GCode/LabelObjects.cpp

@@ -143,6 +143,10 @@ std::string LabelObjects::maybe_change_instance() {
     return "";
 }
 
+bool LabelObjects::has_active_instance() {
+    return this->current_instance != nullptr;
+}
+
 std::string LabelObjects::all_objects_header() const
 {
     if (m_label_objects_style == LabelObjectsStyle::Disabled)

src/libslic3r/GCode/LabelObjects.hpp

@@ -31,6 +31,8 @@ public:
 
     std::string maybe_change_instance();
 
+    bool has_active_instance();
+
 private:
     struct LabelData
     {

src/libslic3r/GCode/WipeTowerIntegration.cpp

@@ -58,23 +58,22 @@ std::string WipeTowerIntegration::append_tcr(GCodeGenerator &gcodegen, const Wip
                                          || will_go_down);       // don't dig into the print
     if (should_travel_to_tower) {
         const Point xy_point = wipe_tower_point_to_object_point(gcodegen, start_pos);
+        gcode += gcodegen.m_label_objects.maybe_stop_instance();
         gcode += gcodegen.retract_and_wipe();
         gcodegen.m_avoid_crossing_perimeters.use_external_mp_once();
         const std::string comment{"Travel to a Wipe Tower"};
         if (gcodegen.m_current_layer_first_position) {
             if (gcodegen.last_position) {
                 gcode += gcodegen.travel_to(
-                    *gcodegen.last_position, xy_point, ExtrusionRole::Mixed, comment,
-                    gcodegen.m_label_objects.maybe_stop_instance()
+                    *gcodegen.last_position, xy_point, ExtrusionRole::Mixed, comment, ""
                 );
             } else {
-                gcode += gcodegen.m_label_objects.maybe_stop_instance();
                 gcode += gcodegen.writer().travel_to_xy(gcodegen.point_to_gcode(xy_point), comment);
                 gcode += gcodegen.writer().get_travel_to_z_gcode(z, comment);
             }
         } else {
             const Vec3crd point = to_3d(xy_point, scaled(z));
-            gcode += gcodegen.travel_to_first_position(point, current_z, gcodegen.m_label_objects.maybe_stop_instance());
+            gcode += gcodegen.travel_to_first_position(point, current_z, "");
         }
         gcode += gcodegen.unretract();
     } else {