Goal Oriented Action Planning

Good morning everyone. It's been about a month, I've been quiet on the blog.  I got myself a new laptop to work on the game sy the times I'd usually write these posts in the bus. As I'll be going to a concert with my wife after work, I left the laptop at home and here I am!

What have I been up to for the last couple of weeks? It's all mainly been about goal oriented action planning (GOAP) AI for the characters in Holocene. This means that the world is a world of states and tasks, but not really in a state machine way. A character has a simple state machine attached, but all it can do is be idle, go somewhere, and perform an action.

Where to go and what to do is dependent on the goals weer formulate.  For instance, the character is hungry. This gives him a goal: eat. Quite simple. So he eats and he's happy. But what happens when the guy does not have food? Well, he needs to eat,  so how do we make that possible?

Any job a character can have consists of the action (removing the food from the inventory and unticking him being hungry) and an effect (he's not hungry), but also some preconditions  (he had food). The action will only run if the character actually had food. 

The thing with GOAP is that once the goal of eating its picked, the character will try to find a sequence of actions leading to having eaten. Via some A* pathfinding algorithm from a tutorial, which I do not yet fully understand,  the character will find a road from the current situation to one where the preconditions for eating are met. We're picking up the apple over there, and we're not attacking the enemy or making fire or building river dykes. Because those won't lead to eating.

The GOAP system makes for flexibility because all you do it formulate small building blocks for behaviour and a system to build sequences of tasks based on very simple nodes. The thing is always that stuff like this isn't as easy as it seems. For instance, right now I'm having trouble making the character understand when a building he's building is finished. I find it hard to debug this system and the fact I don't really understand the underlying pathfinding does not help, but I know what to study and I'll be ok in the end, because I expect it'll all be so much easier once I get it.