Implementing Events Part 1 – Being Stateless

I’ve started implementing the Events feature into Nano. So far my posts haven’t been too technical or in depth, so this one might be a bit heavy for some. First, allow me to describe the overarching idea behind Events in Nano.

The Idea

As a player navigates the world they occasionally encounter an Event upon entering a new location. An Event is basically a description of something that is happening and a list of choices about how to react being made available to the player. Once the player has made a choice they are given some type of result, such as stat alterations, finding treasure, or getting into combat with an enemy.

Example Event

A player enters a new location called ‘The Open Plain’. Upon entering this location they are shown an Event screen, for the event ‘A Pool of Water’. This event has a description; “You see a pool of water. It looks clean enough to drink.” and a couple of choices:
Choice 1: “Drink the water.”
Choice 2: “Ignore the pool of water, bugs have probably pooped in it.”

The player selects Choice 1, “Drink the water.” (Ignoring the possibility of bug poop!). This choice results in the character’s Thirst being reduced by 100. Had the player ignored the water, they would not have received that reward. A second screen is displayed given both a description and a breakdown of the results.

“You drink the bug poop free water. Ahh, refreshing!”
Thirst: -100

How to Organize the Data?

So now that we know the overall idea of what we’re trying to do. How do we execute that in code? It’s never as straightforward as you think and even when you’re prepared for it to become complex, it’ll go and get even more complex than that. This is because at this stage of development I’m really building a system, not just a ‘if this, then that’ scenario.

How does the database look?

First I had to figure out how to organize the information in the database. Will the events, choices and rewards all be in one table or would it be better to have a separate table for each event element?

After a lot of thought, I decided on having separate tables for Events, Event Choices and Choice Rewards. The reason is that each of these has a One-to-Many relationship with the next. For example an Event has many Choices and each Choice can have many Rewards. This would suggest that using a separate table for each piece would be the best way to manage them.

Being Stateless

One major pain that I’m always dealing with in this project is that as a web game using MVC4 and standard postbacks (ie. I’m not using Flash) is that this game is Stateless. Most games can save information about the player’s current location, stat values, and what screen their looking at in your computer’s memory, but not Nano. Nano needs to save all these variables in a database and access that database after every player choice.

Being Stateless Allows Cheating

So given the Stateless limitation, how does the player’s choice get sent back to the server? Another problem with being Stateless is that user input cannot be trusted, they could send any value they want back to the server and the server just accepts that value, never thinking that the user might be a big fat cheater! For example, if a player is in combat and clicks the Use Kick button, the link they click actually forms a URL that ends in /UseCard#CardID=3 which calls the UseCard method with CardID=3 (3 being the ID # for the Kick card).

So there you go, that’s how you can try to exploit Nano. During a combat just change the url to have the CardID equal a number of an amazing card like ‘Sword of a Thousand Truths Stab’ and you can use that card even if it’s not in your hand or even in your deck!

Just kidding, you can’t do any of that because I had to take special measures to stop that form of abuse. Again, because the game is stateless, when the user sends a request to use a card with a particular ID I first check to see if that card is in the user’s hand. If not the user will get a message saying it’s an invalid card and then it will taunt them for trying to cheat. But the point is, this is something many games don’t have to be concerned about since they can store information in memory.

Record the Character’s Current Event

Something that is nice about working in this Stateless environment is that it allows the player to leave the game at any moment and when they return they will be right back where the left off. Whether that is standing in the middle of a forest, at a crucial choice for an event, or right in the middle of combat.

But this also means that the game must record everything to allow for this seamless return. For Events, I decided to add a property to my Character records called ActiveEvent this field stores the ID# of the event that the character is currently involved in. Upon page load the game says “Is the character in an event?” If no, then the ActiveEvent field is null and the game displays the location the character is in. If yes, then the game looks up which event it should display based on this ActiveEvent field.

Sum it up

So that’s how working in a stateless environment for a game adds a layer of complexity to the design of the game. I have to think about everything in steps and each step has to end in a single output of information for the player to react to. In the next post I’ll get into making events more interesting by limiting their frequency and availability.

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