A part of code related to loads after App::OnInit() call is moved from PrusaSlicer.cpp to GUI_App.cpp

Splash Screen under OSX requires a call of wxYeild() for update.
But wxYield() furthers a case, when CallAfter() in CLI::run() was called at the wrong time, before some of the GUI was created.
So, there is workaround:
Parameters needed for later loads are encapsulated to GUI_App::AFTER_INIT_LOADS structure
and are used in GUI_App::AFTER_INIT_LOADS::on_loads which is called just ones after wxEVT_IDLE

src/PrusaSlicer.cpp

@@ -577,6 +577,12 @@ int CLI::run(int argc, char **argv)
 		
 //		gui->autosave = m_config.opt_string("autosave");
         GUI::GUI_App::SetInstance(gui);
+#if ENABLE_GCODE_VIEWER
+        gui->m_after_init_loads.set_params(load_configs, m_extra_config, m_input_files, start_as_gcodeviewer);
+#else
+        gui->m_after_init_loads.set_params(load_configs, m_extra_config, m_input_files);
+#endif // ENABLE_GCODE_VIEWER
+/*
 #if ENABLE_GCODE_VIEWER
         gui->CallAfter([gui, this, &load_configs, start_as_gcodeviewer] {
 #else
@@ -614,6 +620,7 @@ int CLI::run(int argc, char **argv)
             }
 #endif // ENABLE_GCODE_VIEWER
         });
+*/
         int result = wxEntry(argc, argv);
         return result;
 #else /* SLIC3R_GUI */

src/slic3r/GUI/GUI_App.cpp

@@ -123,6 +123,10 @@ public:
 
             memDC.SelectObject(wxNullBitmap);
             set_bitmap(bitmap);
+#ifdef __WXOSX__
+            // without this code splash screen wouldn't be updated under OSX
+            wxYield();
+#endif
         }
     }
 
@@ -531,6 +535,41 @@ static void generic_exception_handle()
     }
 }
 
+void GUI_App::AFTER_INIT_LOADS::on_loads(GUI_App* gui)
+{
+    if (!gui->initialized())
+        return;
+
+#if ENABLE_GCODE_VIEWER
+    if (m_start_as_gcodeviewer) {
+        if (!m_input_files.empty())
+            gui->plater()->load_gcode(wxString::FromUTF8(m_input_files[0].c_str()));
+    }
+    else {
+#endif // ENABLE_GCODE_VIEWER_AS
+#if 0
+        // Load the cummulative config over the currently active profiles.
+        //FIXME if multiple configs are loaded, only the last one will have an effect.
+        // We need to decide what to do about loading of separate presets (just print preset, just filament preset etc).
+        // As of now only the full configs are supported here.
+        if (!m_print_config.empty())
+            gui->mainframe->load_config(m_print_config);
+#endif
+        if (!m_load_configs.empty())
+            // Load the last config to give it a name at the UI. The name of the preset may be later
+            // changed by loading an AMF or 3MF.
+            //FIXME this is not strictly correct, as one may pass a print/filament/printer profile here instead of a full config.
+            gui->mainframe->load_config_file(m_load_configs.back());
+        // If loading a 3MF file, the config is loaded from the last one.
+        if (!m_input_files.empty())
+            gui->plater()->load_files(m_input_files, true, true);
+        if (!m_extra_config.empty())
+            gui->mainframe->load_config(m_extra_config);
+#if ENABLE_GCODE_VIEWER
+    }
+#endif // ENABLE_GCODE_VIEWER
+  }
+
 IMPLEMENT_APP(GUI_App)
 
 #if ENABLE_GCODE_VIEWER
@@ -696,7 +735,6 @@ bool GUI_App::on_init_inner()
         // create splash screen with updated bmp
         scrn = new SplashScreen(bmp.IsOk() ? bmp : create_scaled_bitmap("prusa_slicer_logo", nullptr, 400), 
                                 wxSPLASH_CENTRE_ON_SCREEN | wxSPLASH_TIMEOUT, 4000, splashscreen_pos, is_decorated);
-        wxYield();
         scrn->SetText(_L("Loading configuration..."));
     }
 
@@ -785,6 +823,13 @@ bool GUI_App::on_init_inner()
 
         this->obj_manipul()->update_if_dirty();
 
+        static bool update_gui_after_init = true;
+        if (update_gui_after_init)
+        {
+            update_gui_after_init = false;
+            m_after_init_loads.on_loads(this);
+        }
+
 		// Preset updating & Configwizard are done after the above initializations,
 	    // and after MainFrame is created & shown.
 	    // The extra CallAfter() is needed because of Mac, where this is the only way

src/slic3r/GUI/GUI_App.hpp

@@ -140,6 +140,35 @@ private:
     std::string m_instance_hash_string;
 	size_t m_instance_hash_int;
 
+    // parameters needed for the after OnInit() loads
+    struct AFTER_INIT_LOADS
+    {
+        std::vector<std::string>    m_load_configs;
+        DynamicPrintConfig          m_extra_config;
+        std::vector<std::string>    m_input_files;
+#if ENABLE_GCODE_VIEWER
+        bool                        m_start_as_gcodeviewer;
+#endif // ENABLE_GCODE_VIEWER
+
+        void set_params(
+            const std::vector<std::string>& load_configs,
+            const DynamicPrintConfig&       extra_config,
+            const std::vector<std::string>& input_files,
+#if ENABLE_GCODE_VIEWER
+            bool                            start_as_gcodeviewer
+#endif // ENABLE_GCODE_VIEWER
+        ) {
+            m_load_configs = load_configs;
+            m_extra_config = extra_config;
+            m_input_files = input_files;
+#if ENABLE_GCODE_VIEWER
+            m_start_as_gcodeviewer = start_as_gcodeviewer;
+#endif // ENABLE_GCODE_VIEWER
+        }
+
+        void on_loads(GUI_App* gui);
+    };
+
 public:
     bool            OnInit() override;
     bool            initialized() const { return m_initialized; }
@@ -236,6 +265,7 @@ public:
     PresetUpdater*  preset_updater{ nullptr };
     MainFrame*      mainframe{ nullptr };
     Plater*         plater_{ nullptr };
+    AFTER_INIT_LOADS m_after_init_loads;
 
 	PresetUpdater* get_preset_updater() { return preset_updater; }