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Learning ActionScript 3.0 by Zevan Rosser, Rich Shupe

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Geometry and Trigonometry

While many people find geometry and trigonometry intimidating, the small investment required to understand a few basic principles in these disciplines can pay large dividends. For example, what if you needed to find the distance between two points, or rotate one object around another? These small tasks are needed more often than you may think, and are easier to accomplish than you may realize.

Distance

Let's say you are programming a game in which a character must be pursued by an enemy and must exit through one of two doors to safety. However, the enemy is close enough that the character must choose the nearest exit to survive. The player controls the character, but you must make the game challenging enough for the enemy to catch the character if the player makes the wrong decision. To do that, the enemy must know which exit is closest.

To determine which of two objects (the doors) is closest to a given point (the enemy), you need only one formula called the Pythagorean theorem. Simplified, the theorem says that the length of the longest side of a right triangle is equal to the square root of the sum of the squares of the horizontal and vertical sides. For our needs, this can be determined by finding the differences between the two x values and two y values, and then checking the square root of the sum of those two squares. Figure 7-3 illustrates both descriptions.

Figure 7-3. Calculating the distance between two points using geometry

To determine the distance ...

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