Monday, April 22, 2013

Advancement, Progression and Pacing (Part II)

In Part I of this article, game designer and educator Ian Schreiber explains the reasoning behind using advancement, progression and pacing in games. In Part II, he discusses challenge levels in PvE.

Two Types of Progression 

Progression tends to work differently in PvP games compared to PvE games. In PvP (this includes multi-player PvP like “deathmatch” and also single-player games played against AI opponents), you’re trying to win against another player, human or AI, so the meaning of your progression is relative to the progression of your opponents.

In PvE games (this includes both single-player games and multi-player co-op) you are progressing through the game to try to overcome a challenge and reach some kind of end state, so for most of these games your progress is seen in absolute terms.

Challenge Levels in PvE 

When you’re progressing through a bunch of challenges within a game, how do you track the level of challenge that the player is feeling, so you know if it’s increasing too quickly or too slowly, and whether the total challenge level is just right?

This is actually a tricky question to answer, because the “difficulty” felt by the player is not made up of just one thing here, it’s actually a combination of four things, but the player experiences it only as a single “am I being challenged?” feeling. If we’re trying to measure the player perception of how challenged they are, it’s like if the dashboard of your car took the gas, current speed, and engine RPMs and multiplied them all together to get a single “happiness” rating, and you only had this one number to look at to try to figure out what was causing it to go up or down.

The four components of perceived difficulty

First of all, there’s the level of the player’s skill at the game. The more skilled the player is at the game, the easier the challenges will seem, regardless of anything else.

Second, there’s the player’s power level in the game. Even if the player isn’t very good at the game, doubling their Hit Points will still keep them alive longer, increasing their Attack stat will let them kill things more effectively, giving them a Hook Shot lets them reach new places they couldn’t before, and so on.

Third and fourth, there’s the flip side of both of these, which are how the game creates challenges for the player. The game can create skill-based challenges which require the player to gain a greater amount of skill in the game, for example by introducing new enemies with better AI that make them harder to hit. Or it can provide power-based challenges, by increasing the hit points or attack power or other stats of the enemies in the game (or just adding more enemies in an area) without actually making the enemies any more skilled.

Skill and power are interchangeable

You can substitute skill and power, to an extent, either on the player side or the challenge side. We do this all the time on the challenge side, adding extra hit points or resource generation or otherwise just using the same AI but inflating the numbers, and expecting that the player will need to either get better stats themselves or show a higher level of skill in order to compensate. Or a player who finds a game too easy can challenge themselves by not finding all of the power-ups in a game, giving themselves less power and relying on their high level of skill to make up for it (I’m sure at least some of you have tried beating the original Zelda with just the wooden sword, to see if it could be done). Creating a stronger AI to challenge the player is a lot harder and more expensive, so very few games do that (although the results tend to be spectacular when they do – I’m thinking of Gunstar Heroes as the prototypical example).

At any rate, we can think of the challenge level as the sum of the player’s skill and power, subtracted from the game’s skill challenges and power challenges. This difference gives us the player’s perceived level of difficulty. So, when any one of these things changes, the player will feel the game get harder or easier.

Written mathematically, we have this equation:

PerceivedDifficulty = (SkillChallenge + PowerChallenge) – (PlayerSkill + PlayerPower)

Example: perceived challenge decreases naturally

How do we use this information? Let’s take the player’s skill, which generally increases over time. That’s significant, because it means that if everything else is equal, that is, if the player’s power level, and the overall challenge in the game stay the same, over time the player will feel like the game is getting easier, and eventually it’ll be too easy. To keep the player’s attention once they get better, every game must get harder in some way. (Or at least, every game where the player’s skill can increase. There are some games with no skill component at all, and those are exempted here.)

Measuring the components of perceived challenge

Player skill is hard to measure mathematically on its own, because as I said earlier, it is combined with player power in any game that includes both. For now, I can say that the best way to get a handle on this is to use playtesting and metrics: for example looking at how often players die or are otherwise set back, where these failures happen, how long it takes players to get through a level the first time they encounter it, and so on.

[This article was adapted from Ian Schreiber's course, Game Balance Concepts.]

Ian Schreiber has been in the game industry since the year 2000, first as a programmer and then as a game designer. Also an educator since 2006, Ian has taught game design and development courses at a variety of schools, and on his own without a school. He has co-authored two books, Challenges for Game Designers and Breaking Into the Game Industry.


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