MovieClip._alpha

Availability

Flash Player 4.

Usage

my_mc._alpha:Number

Description

Property; the alpha transparency value of the movie clip specified by my_mc. Valid values are 0 (fully transparent) to 100 (fully opaque). The default value is 100. Objects in a movie clip with _alpha set to 0 are active, even though they are invisible. For example, you can still click a button in a movie clip whose _alpha property is set to 0. To disable the button completely, you can set the movie clip's _visible property to false.

You can extend the methods and event handlers of the MovieClip class by creating a subclass. For more information, see "Assigning a class to a movie clip symbol" in Using ActionScript in Flash.

Example

The following code sets the _alpha property of a dynamically created movie clip named holder_mc to 50% when the mouse rolls over the movie clip. Add the following ActionScript to your FLA or AS file:

this.createEmptyMovieClip("holder_mc", this.getNextHighestDepth());
holder_mc.createEmptyMovieClip("image_mc", holder_mc.getNextHighestDepth());
// replace with your own image or use the following
holder_mc.image_mc.loadMovie("http://www.macromedia.com/devnet/blueprint/articles/nielsen/spotlight_jnielsen.jpg");
holder_mc.onRollOver = function() {
   this._alpha = 50;
};
holder_mc.onRollOut = function() {
   this._alpha = 100;
};

See also

Button._alpha, TextField._alpha, MovieClip._visible

Comments

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mikenicholls said on Jan 20, 2005 at 4:50 PM :

The _alpha property appears to be stored internally as some sort of low precision floating point number, if you set its value you will not always get the same value back. Example: place a movieclip instance called "lomo" on the stage and place this code on frame 1 of the stage:

for(var i=0; i<=100; i++){
_root.lomo._alpha=i;
trace(_root.lomo._alpha);
}

You would expect the numbers 0,1,2,3...100 to be traced, but instead you get the numbers 0,0.78125,1.953125,2.734375...100.

Francis Cheng said on Jan 21, 2005 at 7:58 AM :

The _alpha property is converted internally to an integer color value that ranges from 0 to 255. It loses some precision in this conversion, so when it is converted back to a number between 0 and 100, you get a number that is close to, but not exactly the number you assigned originally. If you need to use the _alpha value later, you can either store it in a separate variable when you set your _alpha or use the Math.round() function when you get the value.

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Current page: http://livedocs.adobe.com/flash/mx2004/main_7_2/00001485.html

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