\u00bb The basics<\/h2>\n
Let’s start with the basics of creating\u00a0one or more NPCs in an SFS2X extension, which is very easy:<\/p>\n
\r\nUser myNpc = getApi().createNPC("npc", getParentZone(), false);\r\n<\/pre>\nEssentially we just need to provide a unique username<\/em>\u00a0and a reference to the current Zone. The last parameter is called forceLogin\u00a0<\/em>and is set to true if you want to kick out another User that exists with the same\u00a0username<\/em>.<\/p>\nIn return this api call gives us a regular\u00a0User<\/strong> object that represents the new (virtual) player and that behaves exactly like any other user in the system. We can join it in a Room, set some User Variables or send chat messages to other people on its behalf.<\/p>\nLike any other client the User object also has a Session<\/strong> object linked\u00a0to it that represents the connection.\u00a0In this case however the Session’s type is set to VOID<\/strong> which indicates\u00a0a connection-less session (i.e. no socket is really used).<\/p>\nYou can verify\u00a0this by running this code and checking out\u00a0the output:<\/p>\n
\r\nSystem.out.println("Session type: " + myNpc.getSession().getType());\r\n<\/pre>\nwhereas a real player will have a Session of type DEFAULT<\/strong> (for TCP), WEBSOCKET<\/strong> or BLUEBOX<\/strong> depending on the type of connection in use.<\/p>\n\u00bb\u00a0Controlling the NPCs<\/h2>\n
There are essentially three modalities\u00a0that we normally employ\u00a0to control non player characters in a game:<\/p>\n
\n- Direct player\/NPC interaction:<\/strong>\u00a0e.g. a player clicks or sends a message to a specific NPC in the game<\/li>\n
- NPC Triggers<\/strong>: a player enters the “range” or Area of Interest \u00a0(AOI) of a certain NPC which in turn activates a reaction (NPC starts shooting or chasing or\u00a0a dialogue is initiated etc…)<\/li>\n
- Independent NPC activity<\/strong>: the NPC is running its own AI logic, unrelated to other player’s actions<\/li>\n<\/ol>\n
Depending on our game complexity and requirements we may to employ\u00a0one, two or all three modalities. Let’s now\u00a0discuss each one a little more in detail and\u00a0see how they should work.<\/p>\n
1) Direct player\/NPC interaction<\/strong><\/p>\n![\"NPC1-zelda\"](\"http:\/\/smartfoxserver.com\/blog\/wp-content\/uploads\/2016\/11\/NPC1-zelda.gif\")
<\/a><\/p>\nThis approach is very\u00a0simple to implement. A\u00a0common use case is a player clicking directly on a character and activating a dialogue or similar action. Since\u00a0the request is initiated by the player we can\u00a0implement this by sending\u00a0an Extension call with the ID of the NPC (user id) and a code for the action to be performed, for example “dialogue”.<\/p>\n
This in turn is\u00a0handled on the server side where a\u00a0dialogue tree is available and the conversation begins. Easy peasy.<\/p>\n
In terms of NPC state it is convenient to attach it directly to the NPC’s User object so that it’s accessible at any time. In other words we can create any class that models our non player character’s state and then store it\u00a0in the User’s object as shown in the following pseudo-code:<\/p>\n
\r\npublic class NpcState\r\n{\r\n\t\/\/ declare fields\r\n\r\n\t\/\/ some methods\r\n\tpublic int getCoins() { ... }\r\n\r\n\tpublic void setCoins(int amount) { ... }\r\n\r\n\tpublic List getInventory() {\u00a0... }\r\n\r\n\tpublic boolean isActive() { ... }\r\n}\r\n\r\n\/\/ attach state to User object\r\nnpcUser.setProperty("state", new NpcState());\r\n\r\n\/\/ ...\r\n\/\/ ...\r\n\/\/ later the object can be accessed and modified\r\n\r\nNpcState state = (NpcState) npcUser.getProperty("state");\r\nstate.setCoins(100);\r\n\r\n<\/pre>\n2) NPC Triggers<\/strong><\/p>\n![\"NPC2-bastion\"](\"http:\/\/smartfoxserver.com\/blog\/wp-content\/uploads\/2016\/11\/NPC2-bastion.jpg\")
<\/a><\/p>\nTriggers will activate NPCs based on different parameters, a typical example is proximity. For instance enemies will detect the player and start shooting or chasing him once he’s close enough.<\/p>\n
To work with triggers we can\u00a0create a basic event system that allows the Extension to send\u00a0internal notifications\u00a0when a certain NPC detects\u00a0a player in its range. This can be implemented in a myriad of ways depending on the nature of the game and its rules, but essentially it boils down to a simple detection loop.<\/p>\n
Here’s a pseudo-code example for a 2D game:<\/p>\n
\r\nvoid onPlayerMove(User user)\r\n{\r\n\tfloat x = user.getVariable("x");\r\n\tfloat y = user.getVariable("y");\r\n\r\n\tfor (User npc : npcList)\r\n\t{\r\n\t\tif (npc.detectPresence(x, y))\r\n\t\t{\r\n\t\t\tdispatchEvent(new DetectionEvent(npc, user));\r\n\t\t}\r\n\t}\r\n}\r\n<\/pre>\nThe onPlayerMove(…)\u00a0<\/strong>method is triggered every time a player changes his position: we loop through all NPCs and check if the player falls within the “detection area” of the NPC. If it does we can dispatch a new event and trigger the specific logic for this occurrence (e.g. the NPC starts chasing the player).<\/p>\nThis approach is\u00a0particularly effective used in conjunction with MMORooms<\/a> and the relative MMO Api<\/a> available in SmartFoxServer 2X. The MMORoom can handle thousands of players by partitioning the virtual 2D\/3D space in smaller sectors and updating players that fall within each other’s AOI.<\/p>\nThis way the loop through an NPC list\u00a0becomes far more optimized as we don’t need to verify every NPC in the Room but only those that are in the immediate surroundings\u00a0of the player.<\/p>\n
![\"NPC3-icewinddale\"](\"http:\/\/smartfoxserver.com\/blog\/wp-content\/uploads\/2016\/11\/NPC3-icewinddale.jpg\")
<\/a><\/p>\n