Export the first M73 line to gcode before custom gcode

xs/src/libslic3r/GCode.cpp

@@ -665,6 +665,14 @@ void GCode::_do_export(Print &print, FILE *file, GCodePreviewData *preview_data)
         _write_format(file, "\n");
     }
     
+    // adds tags for time estimators
+    if (print.config.remaining_times.value)
+    {
+        _writeln(file, GCodeTimeEstimator::Normal_First_M73_Output_Placeholder_Tag);
+        if (m_silent_time_estimator_enabled)
+            _writeln(file, GCodeTimeEstimator::Silent_First_M73_Output_Placeholder_Tag);
+    }
+
     // Prepare the helper object for replacing placeholders in custom G-code and output filename.
     m_placeholder_parser = print.placeholder_parser;
     m_placeholder_parser.update_timestamp();
@@ -724,7 +732,6 @@ void GCode::_do_export(Print &print, FILE *file, GCodePreviewData *preview_data)
     m_placeholder_parser.set("has_wipe_tower", has_wipe_tower);
     m_placeholder_parser.set("has_single_extruder_multi_material_priming", has_wipe_tower && print.config.single_extruder_multi_material_priming);
     std::string start_gcode = this->placeholder_parser_process("start_gcode", print.config.start_gcode.value, initial_extruder_id);
-    
     // Set bed temperature if the start G-code does not contain any bed temp control G-codes.
     this->_print_first_layer_bed_temperature(file, print, start_gcode, initial_extruder_id, true);
     // Set extruder(s) temperature before and after start G-code.

xs/src/libslic3r/GCodeTimeEstimator.cpp

@@ -168,6 +168,9 @@ namespace Slic3r {
     }
 #endif // ENABLE_MOVE_STATS
 
+    const std::string GCodeTimeEstimator::Normal_First_M73_Output_Placeholder_Tag = "; NORMAL_FIRST_M73_OUTPUT_PLACEHOLDER";
+    const std::string GCodeTimeEstimator::Silent_First_M73_Output_Placeholder_Tag = "; SILENT_FIRST_M73_OUTPUT_PLACEHOLDER";
+
     GCodeTimeEstimator::GCodeTimeEstimator(EMode mode)
         : _mode(mode)
     {
@@ -294,7 +297,15 @@ namespace Slic3r {
                 throw std::runtime_error(std::string("Remaining times export failed.\nError while reading from file.\n"));
             }
 
-            gcode_line += "\n";
+            // replaces placeholders for initial line M73 with the real lines
+            if (((_mode == Normal) && (gcode_line == Normal_First_M73_Output_Placeholder_Tag)) ||
+                ((_mode == Silent) && (gcode_line == Silent_First_M73_Output_Placeholder_Tag)))
+            {
+                sprintf(time_line, time_mask.c_str(), std::to_string(0), _get_time_minutes(_time).c_str());
+                gcode_line = time_line;
+            }
+            else
+               gcode_line += "\n";
 
             // add remaining time lines where needed
             _parser.parse_line(gcode_line,

xs/src/libslic3r/GCodeTimeEstimator.hpp

@@ -17,6 +17,9 @@ namespace Slic3r {
     class GCodeTimeEstimator
     {
     public:
+        static const std::string Normal_First_M73_Output_Placeholder_Tag;
+        static const std::string Silent_First_M73_Output_Placeholder_Tag;
+
         enum EMode : unsigned char
         {
             Normal,