Character Trait Model: How Unhappy Is Unhappy

Modelling character traits can be tricky: an example problem has been presented by Jon Ingold in this GDC talk. I discuss the problem below and present a sample model that solves it. I provide an implementation in a C# class.

For character trait one may think of say the character happiness, or a relationship-with-X trait.

The problem is presented from minute 36 of the talk: the first idea that comes to mind in modelling a character trait is by using a number. Greater the number, better the state of the trait. This doesn’t work very well.

How Unhappy is Unhappy

From Jon Ingold GDC talk.

Then Ingold quickly jumps to a proposed solution, which consists in tracking two numbers, positive and negative experiences:

Unhappy vector

From Jon Ingold GDC talk.

Apart from the fact that changes are modelled more appropriately using two variables, what was exactly the problem with using one number?

Here is how I understood the problem: suppose you want to model the happiness of a character in a gameplay. You say that the variable HappinessLevel determines HappinessState according to these values:

HappinessLevel >= 5 = VERY_HAPPY
0 < HappinessLevel < 5 = HAPPY
-5 < HappinessLevel <= 0 = SAD
HappinessLevel <= -5 = SUICIDAL

The character goes through many episodes in two different game-plays: in one the character has 2 positive episodes, and 8 negative ones, and so goes SUICIDAL: 80% of the episodes were negative.

In another gameplay, the character has 20 positive episodes and 25 negative ones. Character is still SUICIDAL, but actually only  55% of episodes were negative! Something clearly does not work :-(

Taking the hint from the talk above, I’ve implemented a generic class model for Character Trait that considers the whole set of the episodes. The set of states and their level can be injected; moreover you can have a “decay %” so that for each new episode, all previous ones have a decay, so older the episode less relevant it gets :-) (by default decay is 1 so its turned off).

You find the class and a test (for Unity) in this zip. It can clearly be refined ad infinitum in function of specific needs, e.g. having episodes that are both positive and negative and so on.

A couple tests:

First test no decay test 1 output
Second test with decay Log with decay

Thanks to Daniele Giardini for campaigning for LINQ removal from the code.

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  1. Pietro Polsinelli says:

    Update: the Character Trait levels can now be values of an type, not just strings so e.g. if you have an enum of states you can use it as a value. Same download:

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