A Simple Trick for Moving Objects in a Physics Simulation

(Original Image by Valerie Everett)

It is sometime necessary to move an object in a physics simulation to a specific point. On the one hand, it can be difficult to analyse the exact force you have to apply; on the other hand it might not look so good if you animate the object’s position directly.

A compromise that works well in many situations is to use a spring-damper system to move the object.

The trick is simple: we apply two forces—the one is proportional to the displacement; the other is proportional to the velocity. Tweaked correctly, they combine to give realistic movement to the desired point.

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Cellular Automata for Simulation in Games

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A cellular automata system is one of the best demonstrations of emergence. If you do not know what cellular automata (CA) is, then you should go download Conway’s Game of Life immediately:

Conway’s Game of Life

Essentially, CA is a collection of state machines, updated in discrete time intervals. The next state of one of these depends on the current state as well as the states of neighbours. Usually, the state machines correspond to cells in a grid, and the neighbours of a cell are the cells connected to that cell. For a more detailed explanation, see the Wikipedia article.

Even simple update rules can lead to interesting behaviour: patterns that cannot be predicted from the rules except by running them. With suitable rules, CA can simulate many systems:

  • Natural phenomena: weather, fire, plant growth, migration patterns, spread of disease.
  • Socio-economic phenomena: urbanisation, segregation, construction and property development, traffic, spread of news.

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