Feature: 'Programming Responsiveness'

If you can't control your actions in a game, might the game be to blame? In this technical article originally published in Game Developer magazine, Neversoft co-founder Mick West examines the problem of response lag in games, along with a number of possible solutions. On responsiveness in games, West makes sure to separate it from human reaction. He notes that humans cannot physically react to visual stimulus by moving their fingers in less than one-tenth of a second: "Game players' peak reaction times vary from 0.15 seconds to 0.30 seconds, depending on how "twitchy" they are. Quantifiables such as these are often brought up when discussing game responsiveness, but the connection is specious. It's not how fast a player reacts to the game; it's how fast the game reacts to the player. The issue is not one of reaction times, but of synchronization. Take Guitar Hero, for example, a game in which symbols come at you, the player, and you have to hit the correct button at a very precise point in time (when the target object is within a particular region). You are anticipating the future event, and there is no reacting involved at all." Problems with lack of responsiveness occur when games fail to react fast enough to players, allowing target objects to move beyond arget regions. Players don't expect objects to move even a few more pixels when they press buttons at the correct time. Because objects generally move at least a few pixels per frame, however, having a few frames of lag can permit the object to drift past its target. "Many action games are based around anticipation and button pressing. In a skateboarding game, you want to jump just before you hit the end of a rail. In a first-person shooter, you fire the instant someone moves in front of your gun. Again, this is not reaction time. You usually have seen the target at least half a second before you shoot it, probably more, and will be either moving the gun, or waiting for the target to move in front of the gun. Because of the somewhat unintuitive nature of these problems with responsiveness, it is important for programmers to fully understand the issues. The most important thing is to be able to clearly describe the frame-by-frame path through logic and rendering that a button-triggered action takes before it creates visual feedback. Once you have this, you can optimize it as close to the optimal pathway as possible." You can now read the full technical Game Developer article to learn about response lag in games as well as a number of possible solutions (no registration required, please feel free to link to this article from other websites).