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Actionscript Cookbook by Joey Lott

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3.6. Setting a Movie Clip’s Transparency

Problem

You want to adjust a movie clip’s transparency.

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( ).

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); ...

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