feat(gui): add 'Follow system theme' option for dark mode

Rebased onto current master and reduced to the feature's own source changes;
removed translation catalogs and unrelated files carried over from the branch base.

Author: BenJule

src/slic3r/GUI/GUI_App.cpp

@@ -3019,11 +3019,18 @@ bool GUI_App::on_init_inner()
     load_language(wxString(), true);
 #ifdef _MSW_DARK_MODE
 
-#ifndef __WINDOWS__
-    wxSystemAppearance app = wxSystemSettings::GetAppearance();
-    GUI::wxGetApp().app_config->set("dark_color_mode", app.IsDark() ? "1" : "0");
-    GUI::wxGetApp().app_config->save();
-#endif // __APPLE__
+    {
+        wxSystemAppearance app = wxSystemSettings::GetAppearance();
+#ifdef __WINDOWS__
+        if (app_config->get("dark_mode_follow_system") == "1") {
+            app_config->set("dark_color_mode", app.IsDark() ? "1" : "0");
+            app_config->save();
+        }
+#else
+        GUI::wxGetApp().app_config->set("dark_color_mode", app.IsDark() ? "1" : "0");
+        GUI::wxGetApp().app_config->save();
+#endif
+    }
 
 
     bool init_dark_color_mode = dark_mode();
@@ -3649,7 +3656,9 @@ bool GUI_App::dark_mode()
     // proper dark mode was first introduced.
     return wxPlatformInfo::Get().CheckOSVersion(10, 14) && mac_dark_mode();
 #else
-    return wxGetApp().app_config->get("dark_color_mode") == "1" ? true : check_dark_mode();
+    if (wxGetApp().app_config->get("dark_mode_follow_system") == "1")
+        return check_dark_mode();
+    return wxGetApp().app_config->get("dark_color_mode") == "1";
     //const unsigned luma = get_colour_approx_luma(wxSystemSettings::GetColour(wxSYS_COLOUR_WINDOW));
     //return luma < 128;
 #endif

src/slic3r/GUI/GUI_Utils.hpp

@@ -201,12 +201,17 @@ template<class P> class DPIAware : public P
 
         this->Bind(wxEVT_SYS_COLOUR_CHANGED, [this](wxSysColourChangedEvent& event)
         {
-#ifndef __WINDOWS__
+#ifdef __WINDOWS__
+            if (GUI::wxGetApp().app_config &&
+                GUI::wxGetApp().app_config->get("dark_mode_follow_system") == "1") {
                 update_dark_config();
                 on_sys_color_changed();
-                event.Skip();
-#endif // __WINDOWS__
-
+            }
+#else
+            update_dark_config();
+            on_sys_color_changed();
+#endif
+            event.Skip();
         });
 
         if (std::is_same<wxDialog, P>::value) {

src/slic3r/GUI/MainFrame.cpp

@@ -2614,10 +2614,8 @@ void MainFrame::on_sys_color_changed()
     // update label colors in respect to the system mode
     wxGetApp().init_label_colours();
 
-#ifndef __WINDOWS__
     wxGetApp().force_colors_update();
     wxGetApp().update_ui_from_settings();
-#endif //__APPLE__
 
 #ifdef __WXMSW__
     wxGetApp().UpdateDarkUI(m_tabpanel);

src/slic3r/GUI/Preferences.hpp

@@ -95,7 +95,8 @@ class PreferencesDialog : public DPIDialog
     // debug mode
     ::CheckBox * m_developer_mode_ckeckbox   = {nullptr};
     ::CheckBox * m_internal_developer_mode_ckeckbox = {nullptr};
-    ::CheckBox * m_dark_mode_ckeckbox        = {nullptr};
+    ::CheckBox * m_dark_mode_ckeckbox               = {nullptr};
+    ::CheckBox * m_dark_mode_follow_system_checkbox = {nullptr};
     ::TextInput *m_backup_interval_textinput = {nullptr};
 
     wxString m_developer_mode_def;