Support for Shift-Tab to loop backward in list of sources.

Mixer.cpp

@@ -642,6 +642,21 @@ void Mixer::setCurrentNext()
     }
 }
 
+void Mixer::setCurrentPrevious()
+{
+    if (session_->numSource() > 0) {
+
+        SourceList::iterator it = current_source_;
+
+        if (it == session_->begin())  {
+            it = session_->end();
+        }
+
+        it--;
+        setCurrentSource( it );
+    }
+}
+
 void Mixer::unsetCurrentSource()
 {
     // discard overlay for previously current source

Mixer.h

@@ -59,6 +59,7 @@ public:
     void setCurrentSource (Node *node);
     void setCurrentSource (uint64_t id);
     void setCurrentNext ();
+    void setCurrentPrevious ();
     void unsetCurrentSource ();
 
     void setCurrentIndex (int index);

UserInterfaceManager.cpp

@@ -382,8 +382,12 @@ void UserInterface::handleKeyboard()
             else if (ImGui::IsKeyPressed( GLFW_KEY_INSERT ))
                 navigator.togglePannelNew();
             // button tab to select next
-            else if (ImGui::IsKeyPressed( GLFW_KEY_TAB ))
-                Mixer::manager().setCurrentNext();
+            else if (ImGui::IsKeyPressed( GLFW_KEY_TAB )) {
+                if (shift_modifier_active)
+                    Mixer::manager().setCurrentPrevious();
+                else
+                    Mixer::manager().setCurrentNext();
+            }
         }
     }