add 'ondefocus' ui event

src/graphics/ui/elements/UINode.cpp

@@ -74,6 +74,11 @@ UINode* UINode::listenDoubleClick(const onaction& action) {
     return this;
 }
 
+UINode* UINode::listenDefocus(const onaction& action) {
+    defocusCallbacks.listen(action);
+    return this;
+}
+
 void UINode::click(int, int) {
     pressed = true;
 }
@@ -98,6 +103,7 @@ bool UINode::isPressed() const {
 
 void UINode::defocus() {
     focused = false;
+    defocusCallbacks.notify(gui);
 }
 
 bool UINode::isFocused() const {

src/graphics/ui/elements/UINode.hpp

@@ -114,6 +114,8 @@ namespace gui {
         ActionsSet actions;
         /// @brief 'ondoubleclick' callbacks
         ActionsSet doubleClickCallbacks;
+        /// @brief 'ondefocus' callbacks
+        ActionsSet defocusCallbacks;
         /// @brief element tooltip text
         std::wstring tooltip;
         /// @brief element tooltip delay
@@ -169,8 +171,9 @@ namespace gui {
         /// @brief Get element z-index
         int getZIndex() const;
 
-        virtual UINode* listenAction(const onaction &action);
+        virtual UINode* listenAction(const onaction& action);
-        virtual UINode* listenDoubleClick(const onaction &action);
+        virtual UINode* listenDoubleClick(const onaction& action);
+        virtual UINode* listenDefocus(const onaction& action);
 
         virtual void onFocus() {focused = true;}
         virtual void doubleClick(int x, int y);

src/graphics/ui/gui_xml.cpp

@@ -180,6 +180,10 @@ static void read_uinode(
         node.listenAction(onclick);
     }
 
+    if (auto ondefocus = create_action(reader, element, "ondefocus")) {
+        node.listenDefocus(ondefocus);
+    }
+
     if (auto ondoubleclick = create_action(reader, element, "ondoubleclick")) {
         node.listenDoubleClick(ondoubleclick);
     }