added timeline slider and export animation frames

engine/node_panel_layer.cpp

@@ -177,6 +177,11 @@ void NodePanelLayer::add_layer()
     add_layer(s);
 }
 
+NodeLayer* NodePanelLayer::get_layer_at(int index)
+{
+    return static_cast<NodeLayer*>(m_layers_container->get_child_at(index));
+}
+
 void NodePanelLayer::remove_layer(NodeLayer* layer)
 {
     auto it = std::find(m_layers.begin(), m_layers.end(), m_current_layer);