add tap event on iOS

src/node_canvas.cpp

@@ -543,6 +543,7 @@ kEventResult NodeCanvas::handle_event(Event* e)
     MouseEvent* me = static_cast<MouseEvent*>(e);
     KeyEvent* ke = static_cast<KeyEvent*>(e);
     GestureEvent* ge = static_cast<GestureEvent*>(e);
+    TouchEvent* te = static_cast<TouchEvent*>(e);
     auto loc = (me->m_pos - m_pos) * root()->m_zoom;
 
     switch (e->m_type)
@@ -631,6 +632,10 @@ kEventResult NodeCanvas::handle_event(Event* e)
         for (auto& mode : *m_canvas->m_mode)
             mode->on_GestureEvent(ge);
         break;
+    case kEventType::TouchTap:
+        if (te->m_finger_count == 2)
+            ActionManager::undo();
+        break;
     default:
         return kEventResult::Available;
         break;