Recipe 3.6 Setting a Movie Clip's Transparency

3.6.1 Problem

You want to adjust a movie clip's transparency.

3.6.2 Solution

Set the _alpha property for the movie clip instance, or set the aa and ab properties of the clip's transform object when using Color.setTransform( ).

3.6.3 Discussion

You can set a movie clip's alpha value (transparency) anywhere from completely transparent (0) to fully opaque (100). The most direct, and generally the most common, way to adjust a movie clip's transparency is by setting the movie clip's _alpha property. You can assign the _alpha property any numeric value, but only values in the range of 0 to 100 will effect a predictable visible change. This sets the clip to be partially transparent:

myMovieClip._alpha = 63;

For more information on how you can animate the _alpha property over time to create fade effects, see Recipe 7.9.

In addition, you can use a Color object to modify a movie clip's transparency. Use a Color object's setTransform( ) method (see Recipe 3.5) to assign color transformations to a movie clip. Among the properties of a color transform object are the aa (alpha offset) and ab (alpha percentage) properties. Therefore, you can use these properties to assign new transparency settings to a movie clip:

// Get the current transform object and modify the aa and ab properties. 
// See Recipe 3.7 for details on modifying a transform object's properties.
my_color = new Color(circle_mc);
transformObj = my_color.getTransform(  );
transformObj.aa = 63;
transformObj.ab = 0;
my_color.setTransform(transformObj);

Modifying a movie clip's alpha using Color.setTransform( ) requires much more code than simply setting the movie clip's _alpha property. However, if you are already setting a movie clip's color values using Color.setTransform( ), it is convenient to set the alpha at the same time using this technique.

Note that all changes made to the MovieClip._alpha property are reflected in the transform object returned by Color.getTransform( ). Similarly, changes made via Color.setTransform( ) are reflected in the MovieClip._alpha property.

3.6.4 See Also

Recipe 7.9 for important information on modifying the _alpha property over time