Actionscript Cookbook

4.7. Drawing a Triangle

Problem

You want to draw a triangle at runtime.

Solution

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

Discussion

You can determine and plot the vertices of a triangle given the lengths of two sides and the angle between them. This is a better approach than specifying the lengths of the three sides because knowing the lengths of two sides and the angle between them always determines a triangle, whereas three arbitrary sides may not fit together to make a triangle.

The custom drawTriangle( ) method accepts six parameters:

ab

The length of the side formed between points a and b, as shown in Figure 4-4.

ac

The length of the side formed between points a and c, as shown in Figure 4-4.

angle

The angle (in degrees) between sides ab and ac.

rotation

The rotation of the triangle in degrees. If 0 or undefined, side ac parallels the x axis.

x

The x coordinate of the centroid (the center point) of the triangle.

y

The y coordinate of the centroid of the triangle.

Figure 4-4. The parameters used in the drawTriangle( ) method

Define the custom drawTriangle( ) 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.drawTriangle = function (ab, ac, angle, rotation, x, y) { // Convert the ...