Interactive Characters

Sometimes, the overall plot arc of the game is fixed and linear, but there are a number of characters (specifically, “non-player characters,” referred to as NPCs) that the player can interact with. In video games, where interpersonal relationships must be quantified, there are two common ways to treat NPCs and their relations with the player.

Flags

A “flag” in this context is just a binary (yes-or-no) value. An action did or did not happen. The player did or did not talk to a certain NPC, and if they did, they either did or did not choose a particular conversation path. As a result, certain new NPCs or conversation options may appear or disappear.

The advantage of flags is that it is very simple to do. Everything either happens or it doesn’t, making the logic that drives the characters pretty easy to follow. It’s also easy to implement in code; programmers can do binary logic easily.

The disadvantage is that there is not a lot of depth to these characters, if there is only black and white and no shades of gray in between. Youcan add more complexity by combining binary values (“only make Aragorn appear if Frodo chose to travel to the Prancing Pony and he successfully avoided capture by the Ringwraith and he puts on the Ring”) but at this point it can get complex to follow, reducing the benefit of simplicity mentioned earlier.

Affinity

Instead of a yes/no dichotomy, use numeric values to measure things like how strongly a character feels affection or hatred towards another character. If you have to decide whether an NPC behaves in a certain way, check to see if its affinity value is past a certain threshold value. (In tabletop RPGs, it is common to also add a die-roll to the mix, so that things may or may not happen based partly on chance.)

The advantage of an affinity system is that it is still fairly simple, it can handle more complexity than a flag system, and it is much more expressive.

However, you must be careful with affinity systems. There is a danger of having a very muddy system (where the player can’t tell why a character behaved in a certain way), especially if several affinity variables or a random die-roll are included in determining the outcome. In short, it is hard to get this kind of system to “feel right” without a lot of playtesting.