Game Development Reference
In-Depth Information
The only choice left is to change the length of each frame by changing the
overall frame rate of the game.
Which frame rate do we choose?
Some look to film or TV for guidance. Films run at 24 fps (frames per
second), and television at 30 fps. These frame rates were chosen because
they are the lower limits required to avoid a perceptive flicker or stutter
between images. But we can't blindly apply these standards to games. The
important delay in TV is between one frame and the next. The important
delay in a game is between the input and the response, which, as we've
seen, is three to four times longer.
Others look at human reaction times for guidance. But this doesn't
work either. The question we're answering has nothing to do with the
player's speed at responding to the game. It has to do with the game's
speed at responding to the player, and whether that's fast enough to feel
smooth and synchronized.
In fact, there's no one standard frame rate at which a game feels right.
Rather, there's a smooth trade-off between graphics and responsiveness.
Every millisecond of extra latency makes a game feel slightly more slug-
gish, while allowing more time to render complicated graphics.
Players learn to give inputs slightly early to compensate for control
latency. The length of a game's control latency determines how far ahead
of time players must anticipate.
For example, imagine a shooter player is moving his crosshairs toward
a target at a constant rate. The player can see that the target is going to
be under the crosshairs in 0.5 seconds. Imagine the game is running at
30 fps and the TV is adding 50 ms of its own lag. This means that the
total input latency is 183 ms (four frames at 1/30 of a second each, plus 50
ms from the TV). If the player fires when he sees his crosshair over the
target, he will miss because his input will not be fed back to the screen
for nearly a fifth of a second. By that time, his crosshair will have passed
the target (ignoring aim assist). So to hit the target, he'll have to learn to
pull the trigger several frames early. Longer latencies mean players must
anticipate farther into the future, which requires more skill and feels less
synchronized.
 
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