Add SetPrimaryEvent and UnsetPrimaryEvent to Module.

include/engine/Module.hpp

@@ -387,6 +387,12 @@ struct Module {
 	*/
 	virtual void onSave(const SaveEvent& e) {}
 
+	struct SetPrimaryEvent {};
+	virtual void onSetPrimary(const SetPrimaryEvent& e) {}
+
+	struct UnsetPrimaryEvent {};
+	virtual void onUnsetPrimary(const UnsetPrimaryEvent& e) {}
+
 	/** DEPRECATED. Override `onAdd(e)` instead. */
 	virtual void onAdd() {}
 	/** DEPRECATED. Override `onRemove(e)` instead. */

src/engine/Engine.cpp

@@ -577,7 +577,20 @@ void Engine::stepBlock(int frames) {
 
 void Engine::setPrimaryModule(Module* module) {
 	WriteLock lock(internal->mutex);
+
+	if (internal->primaryModule) {
+		// Trigger UnsetPrimaryEvent
+		Module::UnsetPrimaryEvent e;
+		internal->primaryModule->onUnsetPrimary(e);
+	}
+
 	internal->primaryModule = module;
+
+	if (internal->primaryModule) {
+		// Trigger SetPrimaryEvent
+		Module::SetPrimaryEvent e;
+		internal->primaryModule->onSetPrimary(e);
+	}
 }