Game Development Reference
In-Depth Information
The opposite of a negative feedback loop is, unsurprisingly, called a
positive feedback
loop
.
Instead of creating balance by acting against the changes that activated the
feedback loop, a positive feedback loop will strengthen the effects that caused it.
Audio feedback is a good example: A microphone picks up a sound, an amplifier
amplifies it, and speakers reproduce the original sound louder. The microphone
then picks up the new sound from the speakers, which gets amplified again, and
so on. The result is a high-pitched shriek that can be stopped only by moving the
microphone away from the speakers.
Positive feedback is also frequently found in games. For example, if you take one
of your opponent's pieces in a game of chess, it becomes easier to take another one
because now you have more pieces than your opponent. Positive feedback creates
volatile systems that can change quickly.
We will be discussing feedback extensively throughout this topic. In most games of
emergence, several different feedback loops operate at the same time. For now, it is
important to remember that in complex systems feedback loops can exist. Negative
feedback loops work toward maintaining a balance in the system, while positive feed-
back loops can destabilize the system.
Different behavioral Patterns emerge at Different Scales
Stephen Wolfram was not the only mathematician to study cellular automata.
Probably the most famous cellular automaton was invented by John Conway and
is called the Game of Life. Conway's automaton consists of cells that are laid out on
a two-dimensional grid. In theory, this grid goes on indefinitely in all directions.
Each cell on the grid has eight neighbors: the cells that surround it orthogonally
and diagonally. Each cell can be in two different states: It is either dead or alive. In
most examples, dead cells are rendered white, while live cells are colored black. Each
iteration the following rules are applied to each cell:
n
A live cell that has fewer than two live neighbors dies from loneliness.
n
A live cell that has more than three live neighbors dies from overcrowding.
T IP
You can down-
load an open-source,
cross-platform version
of the Game of Life at
net.
Wikipedia's entry,
“conway's Game of
Life,” includes links to
a number of other ver-
sions available online.
n
A live cell that has two or three live neighbors stays alive.
n
A dead cell that has exactly three live neighbors becomes alive.
To start the Game of Life, you need to set up a grid and choose a number of cells
that are initially alive. An example of the effects that emerge from applying these
rules is depicted in
Figure 3.5
. However, to really appreciate the emergent behavior
of the Game of Life, we advise you to take a look at one of the many interactive
versions available online.