Using a ScriptableObject Based Inventory System and a FSM to Trigger Interactions

[Kurt-Dekker]

These things (inventory, shop systems, character customization, crafting, etc) are fairly tricky hairy beasts, definitely deep in advanced coding territory.

They contain elements of:

• a database of items that you may possibly possess / equip
• a database of the items that you actually possess / equip currently
• perhaps another database of your “storage” area at home base?
• persistence of this information to storage between game runs
• presentation of the inventory to the user (may have to scale and grow, overlay parts, clothing, etc)
• interaction with items in the inventory or on the character or in the home base storage area
• interaction with the world to get items in and out
• dependence on asset definition (images, etc.) for presentation

Just the design choices of an inventory system can have a lot of complicating confounding issues, such as:

• can you have multiple items? Is there a limit?
• if there is an item limit, what is it? Total count? Weight? Size? Something else?
• are those items shown individually or do they stack?
• are coins / gems stacked but other stuff isn’t stacked?
• do items have detailed data shown (durability, rarity, damage, etc.)?
• can users combine items to make new items? How? Limits? Results? Messages of success/failure?
• can users substantially modify items with other things like spells, gems, sockets, etc.?
• does a worn-out item (shovel) become something else (like a stick) when the item wears out fully?
• etc.

Your best bet is probably to write down exactly what you want feature-wise. It may be useful to get very familiar with an existing game so you have an actual example of each feature in action.

Once you have decided a baseline design, fully work through two or three different inventory tutorials on Youtube, perhaps even for the game example you have chosen above.

Breaking down a large problem such as inventory:

Weapon Inventory and how to script weapons.

You’re welcome of course. One thing you could try to really get a “feel” for what happens in this case is make a simple script that is just one cell of your inventory. Put this into a script that you can access through an “inventory API” that does certain things to a cell. These functions might be: “Set the type of item” “Query the type and quantity of item in this cell” “Add 1 item to this cell.” “Add N number of items to this cell.” “Remove N item from this cell.” Then you can have pr…

If you want to see most of the steps involved, make a “micro inventory” in your game, something whereby the player can have (or not have) a single item, and display that item in the UI, and let the user select that item and do things with it (take, drop, use, wear, eat, sell, buy, etc.).

Everything you learn doing that “micro inventory” of one item will apply when you have any larger more complex inventory, and it will give you a feel for what you are dealing with.

Breaking down large problems in general:

Options for implementing mining/digging in an asteroid belt game?

Whenever engineering seems too much to tackle, it's always best to see if you can break the problem down. What you describe above is by no means simple, as just the different ways all of it could be implemented are complex: does the camera rotate with the player on the asteroid? Do the player's controls rotate as they walk around the asteroid? Does the camera lock to the rotating asteroid? What does the camera do if the player digs down a ways? If the player digs a tunnel into the asteroid,…

As for FSMs, well, I have a position on those too…

I suggest never using the term “state machine.” Instead, just think:

• I have to keep track of some THING(s)
• That THING might change due to reasons
• Depending on that THING, my code might act differently

That’s it. That’s all it is. Really!! The classic example is a door:

• track if it is open or closed
• if it is open, you could close it
• if it is closed, you could open it
• if it is open you could walk through it
• if it is closed you could bump into it

Wanna make it more complex? Put a latch on one side of the door.

This is my position on finite state machines (FSMs) and coding with them:

State machine help

Getting a complex state machine operational is something that you DO NOT want to mix with inheritance if you are presently writing things like “I (probably) understand how inheritance works” Just hard-wire the entire thing and tweak it until it gives EXACTLY the behavior you want. That’s obviously the acid test… it has to first function 100% perfect as you envision it, otherwise what’s the point? In my experience, EVERY single general purpose FSM implementation I have used (without exception)…

I’m kind of more of a “get it working first” guy.

Ask yourself, “WHY would I use FSM solution XYZ when I just need a variable and a switch statement?”

All generic FSM solutions I have seen do not actually improve the problem space.

Your mileage may vary.

“I strongly suggest to make it as simple as possible. No classes, no interfaces, no needless OOP.” - Zajoman on the Unity3D forums.