Lift tool before tool change to avoid material contamination.

src/libslic3r/GCode.cpp

@@ -3164,6 +3164,13 @@ std::string GCodeGenerator::_extrude(
         gcode += this->retract_and_wipe();
         gcode += m_writer.multiple_extruders ? "" : m_label_objects.maybe_change_instance(m_writer);
         gcode += this->m_writer.travel_to_xy(this->point_to_gcode(path.front().point), comment);
+
+        if (!m_pending_pre_extrusion_gcode.empty()) {
+            // There is G-Code that is due to be inserted before an extrusion starts. Insert it before lowering.
+            gcode += m_pending_pre_extrusion_gcode;
+            m_pending_pre_extrusion_gcode.clear();
+        }
+
         gcode += this->m_writer.get_travel_to_z_gcode(z, comment);
     } else if ( this->last_position != path.front().point) {
         std::string comment = "move to first ";
@@ -3689,24 +3696,32 @@ std::string GCodeGenerator::set_extruder(unsigned int extruder_id, double print_
         config.set_key_value("toolchange_z",      new ConfigOptionFloat(print_z));
         config.set_key_value("max_layer_z",       new ConfigOptionFloat(m_max_layer_z));
         toolchange_gcode_parsed = placeholder_parser_process("toolchange_gcode", toolchange_gcode, extruder_id, &config);
-        gcode += toolchange_gcode_parsed;
-        check_add_eol(gcode);
+        check_add_eol(toolchange_gcode_parsed);
+    }
+
+    if (print_z > 0.0) { // ignore lift if this is the first toolchange
+        // Lift the tool right before the change so we don't contaminate colors
+        gcode += m_writer.get_travel_to_z_gcode(print_z + EXTRUDER_CONFIG(travel_max_lift), "Move up before tool change");
     }
 
+    // add the remaining gcode before the next extrusion so the toolchange happens over the correct area
+    std::string pre_extrusion_gcode;
+
     // We inform the writer about what is happening, but we may not use the resulting gcode.
     std::string toolchange_command = m_writer.toolchange(extruder_id);
-    if (! custom_gcode_changes_tool(toolchange_gcode_parsed, m_writer.toolchange_prefix(), extruder_id))
-        gcode += toolchange_command;
-    else {
+    if (!custom_gcode_changes_tool(toolchange_gcode_parsed, m_writer.toolchange_prefix(), extruder_id)) {
+        pre_extrusion_gcode += toolchange_command;
+    } else {
         // user provided his own toolchange gcode, no need to do anything
+        pre_extrusion_gcode += toolchange_gcode_parsed;
     }
 
     // Set the temperature if the wipe tower didn't (not needed for non-single extruder MM)
     if (m_config.single_extruder_multi_material && !m_config.wipe_tower) {
         int temp = (m_layer_index <= 0 ? m_config.first_layer_temperature.get_at(extruder_id) :
                                          m_config.temperature.get_at(extruder_id));
 
-        gcode += m_writer.set_temperature(temp, false);
+        pre_extrusion_gcode += m_writer.set_temperature(temp, false);
     }
 
     this->placeholder_parser().set("current_extruder", extruder_id);
@@ -3720,16 +3735,19 @@ std::string GCodeGenerator::set_extruder(unsigned int extruder_id, double print_
         config.set_key_value("layer_z",   new ConfigOptionFloat(this->writer().get_position().z() - m_config.z_offset.value));
         config.set_key_value("max_layer_z", new ConfigOptionFloat(m_max_layer_z));
         config.set_key_value("filament_extruder_id", new ConfigOptionInt(int(extruder_id)));
-        gcode += this->placeholder_parser_process("start_filament_gcode", start_filament_gcode, extruder_id, &config);
-        check_add_eol(gcode);
+        pre_extrusion_gcode += this->placeholder_parser_process("start_filament_gcode", start_filament_gcode, extruder_id, &config);
+        check_add_eol(pre_extrusion_gcode);
     }
     // Set the new extruder to the operating temperature.
     if (m_ooze_prevention.enable)
-        gcode += m_ooze_prevention.post_toolchange(*this);
+        pre_extrusion_gcode += m_ooze_prevention.post_toolchange(*this);
 
     // The position is now known after the tool change.
     this->last_position = std::nullopt;
 
+    assert(m_pending_pre_extrusion_gcode == NULL);
+    m_pending_pre_extrusion_gcode = pre_extrusion_gcode;
+
     return gcode;
 }