show message dialog about the expected usage when running RT as GIMP plugin

rtdata/languages/default

@@ -2129,3 +2129,5 @@ ZOOMPANEL_ZOOMFITCROPSCREEN;Fit crop to screen\nShortcut: <b>Alt</b>-<b>f</b>
 ZOOMPANEL_ZOOMFITSCREEN;Fit whole image to screen\nShortcut: <b>f</b>
 ZOOMPANEL_ZOOMIN;Zoom In\nShortcut: <b>+</b>
 ZOOMPANEL_ZOOMOUT;Zoom Out\nShortcut: <b>-</b>
+GIMP_PLUGIN_INFO;Welcome to the RawTherapee GIMP plugin!\nOnce you are done editing, simply close the main RawTherapee window and the image will be automatically imported in GIMP.
+DONT_SHOW_AGAIN;Don't show this message again.

rtgui/main.cc

@@ -416,6 +416,19 @@ private:
     RTWindow *rtWindow;
 };
 
+void show_gimp_plugin_info_dialog(Gtk::Window *parent)
+{
+    if (options.gimpPluginShowInfoDialog) {
+        Gtk::MessageDialog info(*parent, M("GIMP_PLUGIN_INFO"), false, Gtk::MESSAGE_INFO, Gtk::BUTTONS_OK, true);
+        Gtk::Box *box = info.get_message_area();
+        Gtk::CheckButton dontshowagain(M("DONT_SHOW_AGAIN"));
+        dontshowagain.show();
+        box->pack_start(dontshowagain);
+        info.run();
+        options.gimpPluginShowInfoDialog = !dontshowagain.get_active();
+    }
+}
+
 } // namespace
 
 
@@ -602,6 +615,9 @@ int main(int argc, char **argv)
             Gtk::Main m(&argc, &argv);
             gdk_threads_enter();
             const std::unique_ptr<RTWindow> rtWindow(create_rt_window());
+            if (gimpPlugin) {
+                show_gimp_plugin_info_dialog(rtWindow.get());
+            }
             m.run(*rtWindow);
             gdk_threads_leave();
 

rtgui/options.cc

@@ -724,6 +724,7 @@ void Options::setDefaults ()
     lastProfilingReferenceDir = "";
     lastBWCurvesDir = "";
     lastLensProfileDir = "";
+    gimpPluginShowInfoDialog = true;
     maxRecentFolders = 15;
 }
 
@@ -1852,6 +1853,9 @@ int Options::readFromFile (Glib::ustring fname)
                 safeDirGet (keyFile, "Dialogs", "LastVibranceCurvesDir", lastVibranceCurvesDir);
                 safeDirGet (keyFile, "Dialogs", "LastProfilingReferenceDir", lastProfilingReferenceDir);
                 safeDirGet (keyFile, "Dialogs", "LastLensProfileDir", lastLensProfileDir);
+                if (keyFile.has_key ("Dialogs", "GimpPluginShowInfoDialog")) {
+                    gimpPluginShowInfoDialog = keyFile.get_boolean("Dialogs", "GimpPluginShowInfoDialog");
+                }
             }
 
 // --------------------------------------------------------------------------------------------------------
@@ -2217,6 +2221,7 @@ int Options::saveToFile (Glib::ustring fname)
         keyFile.set_string ("Dialogs", "LastVibranceCurvesDir", lastVibranceCurvesDir);
         keyFile.set_string ("Dialogs", "LastProfilingReferenceDir", lastProfilingReferenceDir);
         keyFile.set_string ("Dialogs", "LastLensProfileDir", lastLensProfileDir);
+        keyFile.set_boolean("Dialogs", "GimpPluginShowInfoDialog", gimpPluginShowInfoDialog);
 
         keyData = keyFile.to_data ();
 

rtgui/options.h

@@ -315,6 +315,7 @@ public:
     Glib::ustring lastProfilingReferenceDir;
     Glib::ustring lastBWCurvesDir;
     Glib::ustring lastLensProfileDir;
+    bool gimpPluginShowInfoDialog;
 
     size_t maxRecentFolders;                   // max. number of recent folders stored in options file
     std::vector<Glib::ustring> recentFolders;  // List containing all recent folders