Add Core::CancellableEventBase

- Added Core::CancellableEventBase
- Updated Core::EventManager to immediately stop event dispatch if one of listeners set it as cancelled

src/core/event-base.h

@@ -2,6 +2,8 @@
 
 namespace Core
 {
+	class CancellableEventBase;
+
 	template<typename EventT, typename = void>
 	struct EventHasInit : std::false_type {};
 
@@ -20,10 +22,32 @@ namespace Core
 	template<typename EventT>
 	static constexpr bool EventHasDeinit_v = EventHasDeinit<EventT>::value;
 
+	template<typename EventT>
+	using EventIsCancellable = std::is_base_of<CancellableEventBase, EventT>;
+
+	template<typename EventT>
+	constexpr bool EventIsCancellable_v = EventIsCancellable<EventT>::value;
+
+	// Base class for all events. Not to be used directly.
 	class EventBase
 	{
 	protected:
 		EventBase() = default;
 		virtual ~EventBase() = default;
 	};
+
+	// Base class for events that can be cancelled. Not to be used directly.
+	class CancellableEventBase : public EventBase
+	{
+	protected:
+		CancellableEventBase() = default;
+		virtual ~CancellableEventBase() = default;
+
+	public:
+		virtual void Cancel() final { m_cancelled = true; }
+		virtual bool IsCancelled() const final { return m_cancelled; }
+
+	private:
+		bool m_cancelled = false;
+	};
 }

src/core/event-manager.h

@@ -42,6 +42,10 @@ namespace Core {
 			for (auto& wrapper : m_listeners) {
 				wrapper.listener(event);
 
+				if constexpr (EventIsCancellable_v<EventT>) {
+					if (event.IsCancelled()) break;
+				}
+
 				if (wrapper.isToBeRemoved) {
 					spdlog::debug("EventManager: Skipping listener id {} marked for removal for event type: {}", wrapper.id, typeid(EventT).name());
 					continue;