Added opposite action of 'Group all sources'

Mixer action ungroupAll expands all SessionGroupSources.

Mixer.cpp

@@ -794,7 +794,19 @@ void Mixer::groupAll()
     }
 }
 
-void Mixer::flattenSession()
+void Mixer::ungroupAll()
+{
+    for (auto source_iter = session_->begin(); source_iter != session_->end(); source_iter++)
+    {
+        SessionGroupSource *ss = dynamic_cast< SessionGroupSource * >(*source_iter);
+
+        if ( ss != nullptr )
+            import(ss);
+
+    }
+}
+
+void Mixer::groupSession()
 {
     // new session group containing current session
     SessionGroupSource *sessiongroup = new SessionGroupSource;

Mixer.h

@@ -68,8 +68,8 @@ public:
     void deleteSelection  ();
     void groupSelection ();
     void groupAll ();
-
+    void ungroupAll ();
-    void flattenSession();
+    void groupSession ();
 
     // current source
     Source *currentSource ();

UserInterfaceManager.cpp

@@ -989,7 +989,10 @@ void UserInterface::showMenuFile()
         // switch pannel to show first source (created)
         navigator.showPannelSource(0);
     }
-    // TODO : FLATTEN (import all sources from all groups)
+    if (ImGuiToolkit::MenuItemIcon(7, 2, "Expand all groups", false, Mixer::manager().numSource() > 0)) {
+        // create a new group session with all sources
+        Mixer::manager().ungroupAll();
+    }
 
     // HELP AND QUIT
     ImGui::Separator();