Actionscript Cookbook

4.8. Drawing Regular Polygons

Problem

You want to draw a regular polygon (a polygon in which all sides are equal length) at runtime.

Solution

Create a custom MovieClip.drawRegularPolygon( ) method using the Drawing API and invoke it on a movie clip.

Discussion

You can create a method to draw a regular polygon using basic trigonometric ratios to determine the necessary angles and coordinates of the segments.

The drawRegularPolygon( ) accepts five parameters:

sides

The number of sides in the polygon

length

The length of each side in pixels

rotation

The number of degrees by which the polygon should be rotated

x

The x coordinate of the center of the polygon

y

The y coordinate of the center of the polygon

Define the custom drawRegularPolygon( ) method on MovieClip.prototype to make it available to all movie clip instances:

// Include the custom Math library from Chapter 5 to access Math.degToRad(  ).
#include "Math.as"

MovieClip.prototype.drawRegularPolygon = function (sides, length, rotation, x, y) {

  // Convert rotation from degrees to radians.
  rotation = Math.degToRad(rotation);

  // The angle formed between the segments from the polygon's center as shown in 
  // Figure 4-5. Since the total angle in the center is 360 degrees (2π radians), // each segment's angle is 2π divided by the number of sides. var angle = (2 * Math.PI) / sides; // Calculate the length of the radius that circumscribes the polygon (which is also // the distance from the center to any of the vertices). var radius = (length/2)/Math.sin(angle/2); ...