| MovieClip._alpha Property | Flash 4 |
| opacity of a clip or movie | read/write |
The floating-point _alpha property specifies the opacity (or, conversely, the transparency) of mc as a percentage—0 is completely transparent, whereas 100 is completely opaque. Setting the _alpha property of mc affects the visual transparency of all clips nested inside mc but does not affect their _alpha properties. That is, if we have a clip, square, that contains another clip, circle, and we set square._alpha to 50, then circle will be 50% transparent on-screen but will have an _alpha of 100. However, if both circle and its parent clip (square) set their _alpha properties, the effect is cumulative. If each have an _alpha of 50, circle will appear 25% opaque (75% transparent) on-screen. Therefore, don't set the _alpha of nested clips unless they are supposed to have different transparencies from any siblings. To keep it simple, set the _alpha of the parent clip instead.
Note that setting the _alpha of a movie clip affects the aa property of the object returned by Color.getTransform( ).
ball_mc._alpha = 60; // Make ball_mc partially transparent ball_mc._alpha = 0; // Make ball_mc invisible
The following clip event handler makes theClip_mc more transparent as the mouse moves down the screen:
theClip_mc.onEnterFrame = function () {
this._alpha = 100 - (_root._ymouse / 400) * 100;
}
The Color class; MovieClip._visible